Linus Torvalds [Tue, 22 Dec 2020 22:04:25 +0000 (14:04 -0800)]
Merge tag 'kconfig-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kconfig updates from Masahiro Yamada:
- Support only Qt5 for qconf
- Validate signal/slot connection at compile time of qconf
- Sanitize header includes
* tag 'kconfig-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
kconfig: doc: fix $(fileno) to $(filename)
kconfig: fix return value of do_error_if()
kconfig: clean up header inclusion
kconfig: qconf: show Qt version in the About dialog
kconfig: make lkc.h self-sufficient #include-wise
kconfig: qconf: convert to Qt5 new signal/slot connection syntax
kconfig: qconf: use a variable to pass packages to pkg-config
kconfig: qconf: drop Qt4 support
Linus Torvalds [Tue, 22 Dec 2020 21:38:17 +0000 (13:38 -0800)]
Merge branch 'akpm' (patches from Andrew)
Merge KASAN updates from Andrew Morton.
This adds a new hardware tag-based mode to KASAN. The new mode is
similar to the existing software tag-based KASAN, but relies on arm64
Memory Tagging Extension (MTE) to perform memory and pointer tagging
(instead of shadow memory and compiler instrumentation).
By Andrey Konovalov and Vincenzo Frascino.
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (60 commits)
kasan: update documentation
kasan, mm: allow cache merging with no metadata
kasan: sanitize objects when metadata doesn't fit
kasan: clarify comment in __kasan_kfree_large
kasan: simplify assign_tag and set_tag calls
kasan: don't round_up too much
kasan, mm: rename kasan_poison_kfree
kasan, mm: check kasan_enabled in annotations
kasan: add and integrate kasan boot parameters
kasan: inline (un)poison_range and check_invalid_free
kasan: open-code kasan_unpoison_slab
kasan: inline random_tag for HW_TAGS
kasan: inline kasan_reset_tag for tag-based modes
kasan: remove __kasan_unpoison_stack
kasan: allow VMAP_STACK for HW_TAGS mode
kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK
kasan: introduce set_alloc_info
kasan: rename get_alloc/free_info
kasan: simplify quarantine_put call site
kselftest/arm64: check GCR_EL1 after context switch
...
Linus Torvalds [Tue, 22 Dec 2020 21:34:27 +0000 (13:34 -0800)]
Merge tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux
Pull ARM updates from Russell King:
- Rework phys/virt translation
- Add KASan support
- Move DT out of linear map region
- Use more PC-relative addressing in assembly
- Remove FP emulation handling while in kernel mode
- Link with '-z norelro'
- remove old check for GCC <= 4.2 in ARM unwinder code
- disable big endian if using clang's linker
* tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm: (46 commits)
ARM: 9027/1: head.S: explicitly map DT even if it lives in the first physical section
ARM: 9038/1: Link with '-z norelro'
ARM: 9037/1: uncompress: Add OF_DT_MAGIC macro
ARM: 9036/1: uncompress: Fix dbgadtb size parameter name
ARM: 9035/1: uncompress: Add be32tocpu macro
ARM: 9033/1: arm/smp: Drop the macro S(x,s)
ARM: 9032/1: arm/mm: Convert PUD level pgtable helper macros into functions
ARM: 9031/1: hyp-stub: remove unused .L__boot_cpu_mode_offset symbol
ARM: 9044/1: vfp: use undef hook for VFP support detection
ARM: 9034/1: __div64_32(): straighten up inline asm constraints
ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
ARM: 9029/1: Make iwmmxt.S support Clang's integrated assembler
ARM: 9028/1: disable KASAN in call stack capturing routines
ARM: 9026/1: unwind: remove old check for GCC <= 4.2
ARM: 9025/1: Kconfig: CPU_BIG_ENDIAN depends on !LD_IS_LLD
ARM: 9024/1: Drop useless cast of "u64" to "long long"
ARM: 9023/1: Spelling s/mmeory/memory/
ARM: 9022/1: Change arch/arm/lib/mem*.S to use WEAK instead of .weak
ARM: kvm: replace open coded VA->PA calculations with adr_l call
ARM: head.S: use PC relative insn sequence to calculate PHYS_OFFSET
...
Linus Torvalds [Tue, 22 Dec 2020 21:27:21 +0000 (13:27 -0800)]
Merge tag 'for-5.11/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm
Pull device mapper updates from Mike Snitzer:
- Add DM verity support for signature verification with 2nd keyring
- Fix DM verity to skip verity work if IO completes with error while
system is shutting down
- Add new DM multipath "IO affinity" path selector that maps IO
destined to a given path to a specific CPU based on user provided
mapping
- Rename DM multipath path selector source files to have "dm-ps" prefix
- Add REQ_NOWAIT support to some other simple DM targets that don't
block in more elaborate ways waiting for IO
- Export DM crypt's kcryptd workqueue via sysfs (WQ_SYSFS)
- Fix error return code in DM's target_message() if empty message is
received
- A handful of other small cleanups
* tag 'for-5.11/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
dm cache: simplify the return expression of load_mapping()
dm ebs: avoid double unlikely() notation when using IS_ERR()
dm verity: skip verity work if I/O error when system is shutting down
dm crypt: export sysfs of kcryptd workqueue
dm ioctl: fix error return code in target_message
dm crypt: Constify static crypt_iv_operations
dm: add support for REQ_NOWAIT to various targets
dm: rename multipath path selector source files to have "dm-ps" prefix
dm mpath: add IO affinity path selector
dm verity: Add support for signature verification with 2nd keyring
dm: remove unnecessary current->bio_list check when submitting split bio
Linus Torvalds [Tue, 22 Dec 2020 21:24:33 +0000 (13:24 -0800)]
Merge tag 'hwmon-for-v5.11-take2' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging
Pull another hwmon update from Guenter Roeck:
"The only patch in this series is removal of voltage and current
reporting for AMD Zen CPUs.
Turns out that was not worth the trouble, because it's all
undocumented and not maintainable"
* tag 'hwmon-for-v5.11-take2' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging:
hwmon: (k10temp) Remove support for displaying voltage and current on Zen CPUs
Linus Torvalds [Tue, 22 Dec 2020 21:19:43 +0000 (13:19 -0800)]
Merge tag 'dma-mapping-5.11' of git://git.infradead.org/users/hch/dma-mapping
Pull dma-mapping updates from Christoph Hellwig:
- support for a partial IOMMU bypass (Alexey Kardashevskiy)
- add a DMA API benchmark (Barry Song)
- misc fixes (Tiezhu Yang, tangjianqiang)
* tag 'dma-mapping-5.11' of git://git.infradead.org/users/hch/dma-mapping:
selftests/dma: add test application for DMA_MAP_BENCHMARK
dma-mapping: add benchmark support for streaming DMA APIs
dma-contiguous: fix a typo error in a comment
dma-pool: no need to check return value of debugfs_create functions
powerpc/dma: Fallback to dma_ops when persistent memory present
dma-mapping: Allow mixing bypass and mapped DMA operation
Andi Kleen [Tue, 22 Dec 2020 17:40:10 +0000 (09:40 -0800)]
x86/split-lock: Avoid returning with interrupts enabled
When a split lock is detected always make sure to disable interrupts
before returning from the trap handler.
The kernel exit code assumes that all exits run with interrupts
disabled, otherwise the SWAPGS sequence can race against interrupts and
cause recursing page faults and later panics.
The problem will only happen on CPUs with split lock disable
functionality, so Icelake Server, Tiger Lake, Snow Ridge, Jacobsville.
Fixes: ca4c6a9858c2 ("x86/traps: Make interrupt enable/disable symmetric in C code") Fixes: bce9b042ec73 ("x86/traps: Disable interrupts in exc_aligment_check()") # v5.8+ Signed-off-by: Andi Kleen <ak@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Tony Luck <tony.luck@intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Andrey Konovalov [Tue, 22 Dec 2020 20:03:35 +0000 (12:03 -0800)]
kasan: update documentation
This change updates KASAN documentation to reflect the addition of boot
parameters and also reworks and clarifies some of the existing sections,
in particular: defines what a memory granule is, mentions quarantine,
makes Kunit section more readable.
Andrey Konovalov [Tue, 22 Dec 2020 20:03:31 +0000 (12:03 -0800)]
kasan, mm: allow cache merging with no metadata
The reason cache merging is disabled with KASAN is because KASAN puts its
metadata right after the allocated object. When the merged caches have
slightly different sizes, the metadata ends up in different places, which
KASAN doesn't support.
It might be possible to adjust the metadata allocation algorithm and make
it friendly to the cache merging code. Instead this change takes a simpler
approach and allows merging caches when no metadata is present. Which is
the case for hardware tag-based KASAN with kasan.mode=prod.
Andrey Konovalov [Tue, 22 Dec 2020 20:03:28 +0000 (12:03 -0800)]
kasan: sanitize objects when metadata doesn't fit
KASAN marks caches that are sanitized with the SLAB_KASAN cache flag.
Currently if the metadata that is appended after the object (stores e.g.
stack trace ids) doesn't fit into KMALLOC_MAX_SIZE (can only happen with
SLAB, see the comment in the patch), KASAN turns off sanitization
completely.
With this change sanitization of the object data is always enabled.
However the metadata is only stored when it fits. Instead of checking for
SLAB_KASAN flag accross the code to find out whether the metadata is
there, use cache->kasan_info.alloc/free_meta_offset. As 0 can be a valid
value for free_meta_offset, introduce KASAN_NO_FREE_META as an indicator
that the free metadata is missing.
Without this change all sanitized KASAN objects would be put into
quarantine with generic KASAN. With this change, only the objects that
have metadata (i.e. when it fits) are put into quarantine, the rest is
freed right away.
Along the way rework __kasan_cache_create() and add claryfying comments.
Andrey Konovalov [Tue, 22 Dec 2020 20:03:20 +0000 (12:03 -0800)]
kasan: simplify assign_tag and set_tag calls
set_tag() already ignores the tag for the generic mode, so just call it
as is. Add a check for the generic mode to assign_tag(), and simplify its
call in ____kasan_kmalloc().
Andrey Konovalov [Tue, 22 Dec 2020 20:03:17 +0000 (12:03 -0800)]
kasan: don't round_up too much
For hardware tag-based mode kasan_poison_memory() already rounds up the
size. Do the same for software modes and remove round_up() from the common
code.
Andrey Konovalov [Tue, 22 Dec 2020 20:03:13 +0000 (12:03 -0800)]
kasan, mm: rename kasan_poison_kfree
Rename kasan_poison_kfree() to kasan_slab_free_mempool() as it better
reflects what this annotation does. Also add a comment that explains the
PageSlab() check.
Andrey Konovalov [Tue, 22 Dec 2020 20:03:10 +0000 (12:03 -0800)]
kasan, mm: check kasan_enabled in annotations
Declare the kasan_enabled static key in include/linux/kasan.h and in
include/linux/mm.h and check it in all kasan annotations. This allows to
avoid any slowdown caused by function calls when kasan_enabled is
disabled.
Andrey Konovalov [Tue, 22 Dec 2020 20:03:06 +0000 (12:03 -0800)]
kasan: add and integrate kasan boot parameters
Hardware tag-based KASAN mode is intended to eventually be used in
production as a security mitigation. Therefore there's a need for finer
control over KASAN features and for an existence of a kill switch.
This change adds a few boot parameters for hardware tag-based KASAN that
allow to disable or otherwise control particular KASAN features.
The features that can be controlled are:
1. Whether KASAN is enabled at all.
2. Whether KASAN collects and saves alloc/free stacks.
3. Whether KASAN panics on a detected bug or not.
With this change a new boot parameter kasan.mode allows to choose one of
three main modes:
- kasan.mode=off - KASAN is disabled, no tag checks are performed
- kasan.mode=prod - only essential production features are enabled
- kasan.mode=full - all KASAN features are enabled
The chosen mode provides default control values for the features mentioned
above. However it's also possible to override the default values by
providing:
- kasan.stacktrace=off/on - enable alloc/free stack collection
(default: on for mode=full, otherwise off)
- kasan.fault=report/panic - only report tag fault or also panic
(default: report)
If kasan.mode parameter is not provided, it defaults to full when
CONFIG_DEBUG_KERNEL is enabled, and to prod otherwise.
It is essential that switching between these modes doesn't require
rebuilding the kernel with different configs, as this is required by
the Android GKI (Generic Kernel Image) initiative [1].
Andrey Konovalov [Tue, 22 Dec 2020 20:03:03 +0000 (12:03 -0800)]
kasan: inline (un)poison_range and check_invalid_free
Using (un)poison_range() or check_invalid_free() currently results in
function calls. Move their definitions to mm/kasan/kasan.h and turn them
into static inline functions for hardware tag-based mode to avoid
unneeded function calls.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:59 +0000 (12:02 -0800)]
kasan: open-code kasan_unpoison_slab
There's the external annotation kasan_unpoison_slab() that is currently
defined as static inline and uses kasan_unpoison_range(). Open-code this
function in mempool.c. Otherwise with an upcoming change this function
will result in an unnecessary function call.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:56 +0000 (12:02 -0800)]
kasan: inline random_tag for HW_TAGS
Using random_tag() currently results in a function call. Move its
definition to mm/kasan/kasan.h and turn it into a static inline function
for hardware tag-based mode to avoid uneeded function calls.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:52 +0000 (12:02 -0800)]
kasan: inline kasan_reset_tag for tag-based modes
Using kasan_reset_tag() currently results in a function call. As it's
called quite often from the allocator code, this leads to a noticeable
slowdown. Move it to include/linux/kasan.h and turn it into a static
inline function. Also remove the now unneeded reset_tag() internal KASAN
macro and use kasan_reset_tag() instead.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:45 +0000 (12:02 -0800)]
kasan: allow VMAP_STACK for HW_TAGS mode
Even though hardware tag-based mode currently doesn't support checking
vmalloc allocations, it doesn't use shadow memory and works with
VMAP_STACK as is. Change VMAP_STACK definition accordingly.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:42 +0000 (12:02 -0800)]
kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK
There's a config option CONFIG_KASAN_STACK that has to be enabled for
KASAN to use stack instrumentation and perform validity checks for
stack variables.
There's no need to unpoison stack when CONFIG_KASAN_STACK is not enabled.
Only call kasan_unpoison_task_stack[_below]() when CONFIG_KASAN_STACK is
enabled.
Note, that CONFIG_KASAN_STACK is an option that is currently always
defined when CONFIG_KASAN is enabled, and therefore has to be tested
with #if instead of #ifdef.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:34 +0000 (12:02 -0800)]
kasan: rename get_alloc/free_info
Rename get_alloc_info() and get_free_info() to kasan_get_alloc_meta() and
kasan_get_free_meta() to better reflect what those do and avoid confusion
with kasan_set_free_info().
Andrey Konovalov [Tue, 22 Dec 2020 20:02:31 +0000 (12:02 -0800)]
kasan: simplify quarantine_put call site
Patch series "kasan: boot parameters for hardware tag-based mode", v4.
=== Overview
Hardware tag-based KASAN mode [1] is intended to eventually be used in
production as a security mitigation. Therefore there's a need for finer
control over KASAN features and for an existence of a kill switch.
This patchset adds a few boot parameters for hardware tag-based KASAN that
allow to disable or otherwise control particular KASAN features, as well
as provides some initial optimizations for running KASAN in production.
There's another planned patchset what will further optimize hardware
tag-based KASAN, provide proper benchmarking and tests, and will fully
enable tag-based KASAN for production use.
Hardware tag-based KASAN relies on arm64 Memory Tagging Extension (MTE)
[2] to perform memory and pointer tagging. Please see [3] and [4] for
detailed analysis of how MTE helps to fight memory safety problems.
The features that can be controlled are:
1. Whether KASAN is enabled at all.
2. Whether KASAN collects and saves alloc/free stacks.
3. Whether KASAN panics on a detected bug or not.
The patch titled "kasan: add and integrate kasan boot parameters" of this
series adds a few new boot parameters.
kasan.mode allows to choose one of three main modes:
- kasan.mode=off - KASAN is disabled, no tag checks are performed
- kasan.mode=prod - only essential production features are enabled
- kasan.mode=full - all KASAN features are enabled
The chosen mode provides default control values for the features mentioned
above. However it's also possible to override the default values by
providing:
- kasan.stacktrace=off/on - enable stacks collection
(default: on for mode=full, otherwise off)
- kasan.fault=report/panic - only report tag fault or also panic
(default: report)
If kasan.mode parameter is not provided, it defaults to full when
CONFIG_DEBUG_KERNEL is enabled, and to prod otherwise.
It is essential that switching between these modes doesn't require
rebuilding the kernel with different configs, as this is required by
the Android GKI (Generic Kernel Image) initiative.
=== Benchmarks
For now I've only performed a few simple benchmarks such as measuring
kernel boot time and slab memory usage after boot. There's an upcoming
patchset which will optimize KASAN further and include more detailed
benchmarking results.
The benchmarks were performed in QEMU and the results below exclude the
slowdown caused by QEMU memory tagging emulation (as it's different from
the slowdown that will be introduced by hardware and is therefore
irrelevant).
KASAN_HW_TAGS=y + kasan.mode=off introduces no performance or memory
impact compared to KASAN_HW_TAGS=n.
kasan.mode=prod (manually excluding tagging) introduces 3% of performance
and no memory impact (except memory used by hardware to store tags)
compared to kasan.mode=off.
kasan.mode=full has about 40% performance and 30% memory impact over
kasan.mode=prod. Both come from alloc/free stack collection.
kselftest/arm64: check GCR_EL1 after context switch
This test is specific to MTE and verifies that the GCR_EL1 register is
context switched correctly.
It spawns 1024 processes and each process spawns 5 threads. Each thread
writes a random setting of GCR_EL1 through the prctl() system call and
reads it back verifying that it is the same. If the values are not the
same it reports a failure.
Note: The test has been extended to verify that even SYNC and ASYNC mode
setting is preserved correctly over context switching.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:17 +0000 (12:02 -0800)]
kasan, mm: reset tags when accessing metadata
Kernel allocator code accesses metadata for slab objects, that may lie
out-of-bounds of the object itself, or be accessed when an object is
freed. Such accesses trigger tag faults and lead to false-positive
reports with hardware tag-based KASAN.
Software KASAN modes disable instrumentation for allocator code via
KASAN_SANITIZE Makefile macro, and rely on kasan_enable/disable_current()
annotations which are used to ignore KASAN reports.
With hardware tag-based KASAN neither of those options are available, as
it doesn't use compiler instrumetation, no tag faults are ignored, and MTE
is disabled after the first one.
Instead, reset tags when accessing metadata (currently only for SLUB).
Andrey Konovalov [Tue, 22 Dec 2020 20:02:13 +0000 (12:02 -0800)]
kasan, arm64: print report from tag fault handler
Add error reporting for hardware tag-based KASAN. When
CONFIG_KASAN_HW_TAGS is enabled, print KASAN report from the arm64 tag
fault handler.
SAS bits aren't set in ESR for all faults reported in EL1, so it's
impossible to find out the size of the access the caused the fault. Adapt
KASAN reporting code to handle this case.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:10 +0000 (12:02 -0800)]
kasan, arm64: implement HW_TAGS runtime
Provide implementation of KASAN functions required for the hardware
tag-based mode. Those include core functions for memory and pointer
tagging (tags_hw.c) and bug reporting (report_tags_hw.c). Also adapt
common KASAN code to support the new mode.
Andrey Konovalov [Tue, 22 Dec 2020 20:02:06 +0000 (12:02 -0800)]
kasan, arm64: expand CONFIG_KASAN checks
Some #ifdef CONFIG_KASAN checks are only relevant for software KASAN modes
(either related to shadow memory or compiler instrumentation). Expand
those into CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS.
Andrey Konovalov [Tue, 22 Dec 2020 20:01:56 +0000 (12:01 -0800)]
arm64: kasan: add arch layer for memory tagging helpers
This patch add a set of arch_*() memory tagging helpers currently only
defined for arm64 when hardware tag-based KASAN is enabled. These helpers
will be used by KASAN runtime to implement the hardware tag-based mode.
The arch-level indirection level is introduced to simplify adding hardware
tag-based KASAN support for other architectures in the future by defining
the appropriate arch_*() macros.
Andrey Konovalov [Tue, 22 Dec 2020 20:01:52 +0000 (12:01 -0800)]
arm64: kasan: align allocations for HW_TAGS
Hardware tag-based KASAN uses the memory tagging approach, which requires
all allocations to be aligned to the memory granule size. Align the
allocations to MTE_GRANULE_SIZE via ARCH_SLAB_MINALIGN when
CONFIG_KASAN_HW_TAGS is enabled.
kasan, mm: untag page address in free_reserved_area
free_reserved_area() memsets the pages belonging to a given memory area.
As that memory hasn't been allocated via page_alloc, the KASAN tags that
those pages have are 0x00. As the result the memset might result in a tag
mismatch.
arm64: mte: switch GCR_EL1 in kernel entry and exit
When MTE is present, the GCR_EL1 register contains the tags mask that
allows to exclude tags from the random generation via the IRG instruction.
With the introduction of the new Tag-Based KASAN API that provides a
mechanism to reserve tags for special reasons, the MTE implementation has
to make sure that the GCR_EL1 setting for the kernel does not affect the
userspace processes and viceversa.
Save and restore the kernel/user mask in GCR_EL1 in kernel entry and exit.
The gcr_user mask is a per thread mask that represents the tags that are
excluded from random generation when the Memory Tagging Extension is
present and an 'irg' instruction is invoked.
gcr_user affects the behavior on EL0 only.
Currently that mask is an include mask and it is controlled by the user
via prctl() while GCR_EL1 accepts an exclude mask.
Convert the include mask into an exclude one to make it easier the
register setting.
Note: This change will affect gcr_kernel (for EL1) introduced with a
future patch.
Hardware tag-based KASAN relies on Memory Tagging Extension (MTE) feature
and requires it to be enabled. MTE supports
This patch adds a new mte_enable_kernel() helper, that enables MTE in
Synchronous mode in EL1 and is intended to be called from KASAN runtime
during initialization.
The Tag Checking operation causes a synchronous data abort as a
consequence of a tag check fault when MTE is configured in synchronous
mode.
As part of this change enable match-all tag for EL1 to allow the kernel to
access user pages without faulting. This is required because the kernel
does not have knowledge of the tags set by the user in a page.
Note: For MTE, the TCF bit field in SCTLR_EL1 affects only EL1 in a
similar way as TCF0 affects EL0.
MTE that is built on top of the Top Byte Ignore (TBI) feature hence we
enable it as part of this patch as well.
The hardware tag-based KASAN for compatibility with the other modes stores
the tag associated to a page in page->flags. Due to this the kernel
faults on access when it allocates a page with an initial tag and the user
changes the tags.
Reset the tag associated by the kernel to a page in all the meaningful
places to prevent kernel faults on access.
Note: An alternative to this approach could be to modify page_to_virt().
This though could end up being racy, in fact if a CPU checks the
PG_mte_tagged bit and decides that the page is not tagged but another CPU
maps the same with PROT_MTE and becomes tagged the subsequent kernel
access would fail.
Provide helper functions to manipulate allocation and pointer tags for
kernel addresses.
Low-level helper functions (mte_assign_*, written in assembly) operate tag
values from the [0x0, 0xF] range. High-level helper functions
(mte_get/set_*) use the [0xF0, 0xFF] range to preserve compatibility with
normal kernel pointers that have 0xFF in their top byte.
MTE_GRANULE_SIZE and related definitions are moved to mte-def.h header
that doesn't have any dependencies and is safe to include into any
low-level header.
Andrey Konovalov [Tue, 22 Dec 2020 20:01:20 +0000 (12:01 -0800)]
kasan: introduce CONFIG_KASAN_HW_TAGS
This patch adds a configuration option for a new KASAN mode called
hardware tag-based KASAN. This mode uses the memory tagging approach like
the software tag-based mode, but relies on arm64 Memory Tagging Extension
feature for tag management and access checking.
Andrey Konovalov [Tue, 22 Dec 2020 20:01:17 +0000 (12:01 -0800)]
kasan: separate metadata_fetch_row for each mode
This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.
Rework print_memory_metadata() to make it agnostic with regard to the way
metadata is stored. Allow providing a separate metadata_fetch_row()
implementation for each KASAN mode. Hardware tag-based KASAN will provide
its own implementation that doesn't use shadow memory.
Andrey Konovalov [Tue, 22 Dec 2020 20:01:03 +0000 (12:01 -0800)]
kasan, arm64: rename kasan_init_tags and mark as __init
Rename kasan_init_tags() to kasan_init_sw_tags() as the upcoming hardware
tag-based KASAN mode will have its own initialization routine. Also
similarly to kasan_init() mark kasan_init_tags() as __init.
Andrey Konovalov [Tue, 22 Dec 2020 20:01:00 +0000 (12:01 -0800)]
kasan, arm64: move initialization message
Software tag-based KASAN mode is fully initialized with kasan_init_tags(),
while the generic mode only requires kasan_init(). Move the
initialization message for tag-based mode into kasan_init_tags().
Also fix pr_fmt() usage for KASAN code: generic.c doesn't need it as it
doesn't use any printing functions; tag-based mode should use "kasan:"
instead of KBUILD_MODNAME (which stands for file name).
Andrey Konovalov [Tue, 22 Dec 2020 20:00:46 +0000 (12:00 -0800)]
kasan: hide invalid free check implementation
This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.
For software KASAN modes the check is based on the value in the shadow
memory. Hardware tag-based KASAN won't be using shadow, so hide the
implementation of the check in check_invalid_free().
Also simplify the code for software tag-based mode.
Andrey Konovalov [Tue, 22 Dec 2020 20:00:39 +0000 (12:00 -0800)]
kasan: rename report and tags files
Rename generic_report.c to report_generic.c and tags_report.c to
report_sw_tags.c, as their content is more relevant to report.c file.
Also rename tags.c to sw_tags.c to better reflect that this file contains
code for software tag-based mode.
Andrey Konovalov [Tue, 22 Dec 2020 20:00:35 +0000 (12:00 -0800)]
kasan: define KASAN_MEMORY_PER_SHADOW_PAGE
Define KASAN_MEMORY_PER_SHADOW_PAGE as (KASAN_GRANULE_SIZE << PAGE_SHIFT),
which is the same as (KASAN_GRANULE_SIZE * PAGE_SIZE) for software modes
that use shadow memory, and use it across KASAN code to simplify it.
Andrey Konovalov [Tue, 22 Dec 2020 20:00:32 +0000 (12:00 -0800)]
kasan: split out shadow.c from common.c
This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.
The new mode won't be using shadow memory. Move all shadow-related code
to shadow.c, which is only enabled for software KASAN modes that use
shadow memory.
Andrey Konovalov [Tue, 22 Dec 2020 20:00:24 +0000 (12:00 -0800)]
kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_*
This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.
The new mode won't be using shadow memory, but will still use the concept
of memory granules. Each memory granule maps to a single metadata entry:
8 bytes per one shadow byte for generic mode, 16 bytes per one shadow byte
for software tag-based mode, and 16 bytes per one allocation tag for
hardware tag-based mode.
Rename KASAN_SHADOW_SCALE_SIZE to KASAN_GRANULE_SIZE, and
KASAN_SHADOW_MASK to KASAN_GRANULE_MASK.
Also use MASK when used as a mask, otherwise use SIZE.
Andrey Konovalov [Tue, 22 Dec 2020 20:00:21 +0000 (12:00 -0800)]
kasan: rename (un)poison_shadow to (un)poison_range
This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.
The new mode won't be using shadow memory. Rename external annotation
kasan_unpoison_shadow() to kasan_unpoison_range(), and introduce internal
functions (un)poison_range() (without kasan_ prefix).
Andrey Konovalov [Tue, 22 Dec 2020 20:00:07 +0000 (12:00 -0800)]
kasan: drop unnecessary GPL text from comment headers
Patch series "kasan: add hardware tag-based mode for arm64", v11.
This patchset adds a new hardware tag-based mode to KASAN [1]. The new
mode is similar to the existing software tag-based KASAN, but relies on
arm64 Memory Tagging Extension (MTE) [2] to perform memory and pointer
tagging (instead of shadow memory and compiler instrumentation).
This patchset is co-developed and tested by
Vincenzo Frascino <vincenzo.frascino@arm.com>.
The underlying ideas of the approach used by hardware tag-based KASAN are:
1. By relying on the Top Byte Ignore (TBI) arm64 CPU feature, pointer tags
are stored in the top byte of each kernel pointer.
2. With the Memory Tagging Extension (MTE) arm64 CPU feature, memory tags
for kernel memory allocations are stored in a dedicated memory not
accessible via normal instuctions.
3. On each memory allocation, a random tag is generated, embedded it into
the returned pointer, and the corresponding memory is tagged with the
same tag value.
4. With MTE the CPU performs a check on each memory access to make sure
that the pointer tag matches the memory tag.
5. On a tag mismatch the CPU generates a tag fault, and a KASAN report is
printed.
Same as other KASAN modes, hardware tag-based KASAN is intended as a
debugging feature at this point.
====== Rationale
There are two main reasons for this new hardware tag-based mode:
1. Previously implemented software tag-based KASAN is being successfully
used on dogfood testing devices due to its low memory overhead (as
initially planned). The new hardware mode keeps the same low memory
overhead, and is expected to have significantly lower performance
impact, due to the tag checks being performed by the hardware.
Therefore the new mode can be used as a better alternative in dogfood
testing for hardware that supports MTE.
2. The new mode lays the groundwork for the planned in-kernel MTE-based
memory corruption mitigation to be used in production.
====== Technical details
Considering the implementation perspective, hardware tag-based KASAN is
almost identical to the software mode. The key difference is using MTE
for assigning and checking tags.
Compared to the software mode, the hardware mode uses 4 bits per tag, as
dictated by MTE. Pointer tags are stored in bits [56:60), the top 4 bits
have the normal value 0xF. Having less distict tags increases the
probablity of false negatives (from ~1/256 to ~1/16) in certain cases.
Only synchronous exceptions are set up and used by hardware tag-based KASAN.
====== Benchmarks
Note: all measurements have been performed with software emulation of Memory
Tagging Extension, performance numbers for hardware tag-based KASAN on the
actual hardware are expected to be better.
Boot time [1]:
* 2.8 sec for clean kernel
* 5.7 sec for hardware tag-based KASAN
* 11.8 sec for software tag-based KASAN
* 11.6 sec for generic KASAN
Slab memory usage after boot [2]:
* 7.0 kb for clean kernel
* 9.7 kb for hardware tag-based KASAN
* 9.7 kb for software tag-based KASAN
* 41.3 kb for generic KASAN
Measurements have been performed with:
* defconfig-based configs
* Manually built QEMU master
* QEMU arguments: -machine virt,mte=on -cpu max
* CONFIG_KASAN_STACK_ENABLE disabled
* CONFIG_KASAN_INLINE enabled
* clang-10 as the compiler and gcc-10 as the assembler
[1] Time before the ext4 driver is initialized.
[2] Measured as `cat /proc/meminfo | grep Slab`.
====== Notes
The cover letter for software tag-based KASAN patchset can be found here:
Guenter Roeck [Mon, 14 Dec 2020 18:26:22 +0000 (10:26 -0800)]
hwmon: (k10temp) Remove support for displaying voltage and current on Zen CPUs
Voltages and current are reported by Zen CPUs. However, the means
to do so is undocumented, changes from CPU to CPU, and the raw data
is not calibrated. Calibration information is available, but again
not documented. This results in less than perfect user experience,
up to concerns that loading the driver might possibly damage
the hardware (by reporting out-of range voltages). Effectively
support for reporting voltages and current is not maintainable.
Drop it.
dm ebs: avoid double unlikely() notation when using IS_ERR()
The definition of IS_ERR() already applies the unlikely() notation
when checking the error status of the passed pointer. For this
reason there is no need to have the same notation outside of
IS_ERR() itself.
Clean up code by removing redundant notation.
Signed-off-by: Antonio Quartulli <a@unstable.cc> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Hyeongseok Kim [Thu, 3 Dec 2020 00:46:59 +0000 (09:46 +0900)]
dm verity: skip verity work if I/O error when system is shutting down
If emergency system shutdown is called, like by thermal shutdown,
a dm device could be alive when the block device couldn't process
I/O requests anymore. In this state, the handling of I/O errors
by new dm I/O requests or by those already in-flight can lead to
a verity corruption state, which is a misjudgment.
So, skip verity work in response to I/O error when system is shutting
down.
Signed-off-by: Hyeongseok Kim <hyeongseok@gmail.com> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Linus Torvalds [Mon, 21 Dec 2020 18:39:37 +0000 (10:39 -0800)]
Merge tag 'clk-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux
Pull clk updates from Stephen Boyd:
"The core framework got some nice improvements this time around. We
gained the ability to get struct clk pointers from a struct clk_hw so
that clk providers can consume the clks they provide, if they need to
do something like that. This has been a long missing part of the clk
provider API that will help us move away from exposing a struct clk
pointer in the struct clk_hw. Tracepoints are added for the
clk_set_rate() "range" functions, similar to the tracepoints we
already have for clk_set_rate() and we added a column to debugfs to
help developers understand the hardware enable state of clks in case
firmware or bootloader state is different than what is expected.
Overall the core changes are mostly improving the clk driver writing
experience.
At the driver level, we have the usual collection of driver updates
and new drivers for new SoCs. This time around the Qualcomm folks
introduced a good handful of clk drivers for various parts of three or
four SoCs. The SiFive folks added a new clk driver for their FU740
SoCs, coming in second on the diffstat and then Atmel AT91 and Amlogic
SoCs had lots of work done after that for various new features. One
last thing to note in the driver area is that the i.MX driver has
gained a new binding to support SCU clks after being on the list for
many months. It uses a two cell binding which is sort of rare in clk
DT bindings. Beyond that we have the usual set of driver fixes and
tweaks that come from more testing and finding out that some
configuration was wrong or that a driver could support being built as
a module.
Summary:
Core:
- Add some trace points for clk_set_rate() "range" functions
- Add hardware enable information to clk_summary debugfs
- Replace clk-provider.h with of_clk.h when possible
- Add devm variant of clk_notifier_register()
- Add clk_hw_get_clk() to generate a struct clk from a struct clk_hw
New Drivers:
- Bindings for Canaan K210 SoC clks
- Support for SiFive FU740 PRCI
- Camera clks on Qualcomm SC7180 SoCs
- GCC and RPMh clks on Qualcomm SDX55 SoCs
- RPMh clks on Qualcomm SM8350 SoCs
- LPASS clks on Qualcomm SM8250 SoCs
Updates:
- DVFS support for AT91 clk driver
- Update git repo branch for Renesas clock drivers
- Add camera (CSI) and video-in (VIN) clocks on Renesas R-Car V3U
- Add RPC (QSPI/HyperFLASH) clocks on Renesas RZ/G2M, RZ/G2N, and RZ/G2E
- Stop using __raw_*() I/O accessors in Renesas clk drivers
- One more conversion of DT bindings to json-schema
- Make i.MX clk-gate2 driver more flexible
- New two cell binding for i.MX SCU clks
- Drop of_match_ptr() in i.MX8 clk drivers
- Add arch dependencies for Rockchip clk drivers
- Fix i2s on Rockchip rk3066
- Add MIPI DSI clks on Amlogic axg and g12 SoCs
- Support modular builds of Amlogic clk drivers
- Fix an Amlogic Video PLL clock dependency
- Samsung Kconfig dependencies updates for better compile test coverage
- Refactoring of the Samsung PLL clocks driver
- Small Tegra driver cleanups
- Minor fixes to Ingenic and VC5 clk drivers
- Cleanup patches to remove unused variables and plug memory leaks"
* tag 'clk-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux: (134 commits)
dt-binding: clock: Document canaan,k210-clk bindings
dt-bindings: Add Canaan vendor prefix
clk: vc5: Use "idt,voltage-microvolt" instead of "idt,voltage-microvolts"
clk: ingenic: Fix divider calculation with div tables
clk: sunxi-ng: Make sure divider tables have sentinel
clk: s2mps11: Fix a resource leak in error handling paths in the probe function
clk: mvebu: a3700: fix the XTAL MODE pin to MPP1_9
clk: si5351: Wait for bit clear after PLL reset
clk: at91: sam9x60: remove atmel,osc-bypass support
clk: at91: sama7g5: register cpu clock
clk: at91: clk-master: re-factor master clock
clk: at91: sama7g5: do not allow cpu pll to go higher than 1GHz
clk: at91: sama7g5: decrease lower limit for MCK0 rate
clk: at91: sama7g5: remove mck0 from parent list of other clocks
clk: at91: clk-sam9x60-pll: allow runtime changes for pll
clk: at91: sama7g5: add 5th divisor for mck0 layout and characteristics
clk: at91: clk-master: add 5th divisor for mck master
clk: at91: sama7g5: allow SYS and CPU PLLs to be exported and referenced in DT
dt-bindings: clock: at91: add sama7g5 pll defines
clk: at91: sama7g5: fix compilation error
...
Linus Torvalds [Mon, 21 Dec 2020 18:35:11 +0000 (10:35 -0800)]
Merge tag 'm68knommu-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu
Pull m68knommu updates from Greg Ungerer:
- cleanup of 68328 code
- align BSS section to 32bit
* tag 'm68knommu-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu:
m68k: m68328: remove duplicate code
m68k: m68328: move platform code to separate files
m68knommu: align BSS section to 4-byte boundaries
Linus Torvalds [Mon, 21 Dec 2020 18:28:02 +0000 (10:28 -0800)]
Merge tag '9p-for-5.11-rc1' of git://github.com/martinetd/linux
Pull 9p update from Dominique Martinet:
- fix long-standing limitation on open-unlink-fop pattern
- add refcount to p9_fid (fixes the above and will allow for more
cleanups and simplifications in the future)
* tag '9p-for-5.11-rc1' of git://github.com/martinetd/linux:
9p: Remove unnecessary IS_ERR() check
9p: Uninitialized variable in v9fs_writeback_fid()
9p: Fix writeback fid incorrectly being attached to dentry
9p: apply review requests for fid refcounting
9p: add refcount to p9_fid struct
fs/9p: search open fids first
fs/9p: track open fids
fs/9p: fix create-unlink-getattr idiom
Ard Biesheuvel [Tue, 17 Nov 2020 07:41:01 +0000 (08:41 +0100)]
ARM: 9027/1: head.S: explicitly map DT even if it lives in the first physical section
The early ATAGS/DT mapping code uses SECTION_SHIFT to mask low order
bits of R2, and decides that no ATAGS/DTB were provided if the resulting
value is 0x0.
This means that on systems where DRAM starts at 0x0 (such as Raspberry
Pi), no explicit mapping of the DT will be created if R2 points into the
first 1 MB section of memory. This was not a problem before, because the
decompressed kernel is loaded at the base of DRAM and mapped using
sections as well, and so as long as the DT is referenced via a virtual
address that uses the same translation (the linear map, in this case),
things work fine.
However, commit 7a1be318f579 ("9012/1: move device tree mapping out of
linear region") changes this, and now the DT is referenced via a virtual
address that is disjoint from the linear mapping of DRAM, and so we need
the early code to create the DT mapping unconditionally.
So let's create the early DT mapping for any value of R2 != 0x0.
Reported-by: "kernelci.org bot" <bot@kernelci.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
When linking a multi_v7_defconfig + CONFIG_KASAN=y kernel with
LD=ld.lld, the following error occurs:
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 zImage
ld.lld: error: section: .exit.data is not contiguous with other relro sections
LLD defaults to '-z relro', which is unneeded for the kernel because
program headers are not used nor is there any position independent code
generation or linking for ARM. Add '-z norelro' to LDFLAGS_vmlinux to
avoid this error.
Link: https://github.com/ClangBuiltLinux/linux/issues/1189 Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
The DTB magic marker is stored as a 32-bit big-endian value, and thus
depends on the CPU's endianness. Add a macro to define this value in
native endianness, to reduce #ifdef clutter and (future) duplication.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Nicolas Pitre <nico@fluxnic.net> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Mapping between IPI type index and its string is direct without requiring
an additional offset. Hence the existing macro S(x, s) is now redundant
and can just be dropped. This also makes the code clean and simple.
Cc: Marc Zyngier <maz@kernel.org> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Macros used as functions can be problematic from the compiler perspective.
There was a build failure report caused primarily because of non reference
of an argument variable. Hence convert PUD level pgtable helper macros into
functions in order to avoid such problems in the future. In the process, it
fixes the argument variables sequence in set_pud() which probably remained
hidden for being a macro.
Ard Biesheuvel [Fri, 27 Nov 2020 12:07:22 +0000 (13:07 +0100)]
ARM: 9031/1: hyp-stub: remove unused .L__boot_cpu_mode_offset symbol
Commit aaac3733171fca94 ("ARM: kvm: replace open coded VA->PA calculations
with adr_l call") removed all uses of .L__boot_cpu_mode_offset, so there
is no longer a need to define it.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Ard Biesheuvel [Sat, 19 Dec 2020 15:29:58 +0000 (16:29 +0100)]
ARM: 9044/1: vfp: use undef hook for VFP support detection
Commit f77ac2e378be9dd6 ("ARM: 9030/1: entry: omit FP emulation for UND
exceptions taken in kernel mode") failed to take into account that there
is in fact a case where we relied on this code path: during boot, the
VFP detection code issues a read of FPSID, which will trigger an undef
exception on cores that lack VFP support.
So let's reinstate this logic using an undef hook which is registered
only for the duration of the initcall to vpf_init(), and which sets
VFP_arch to a non-zero value - as before - if no VFP support is present.
Fixes: f77ac2e378be9dd6 ("ARM: 9030/1: entry: omit FP emulation for UND ...") Reported-by: "kernelci.org bot" <bot@kernelci.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Masahiro Yamada [Sat, 19 Dec 2020 18:18:42 +0000 (03:18 +0900)]
kconfig: fix return value of do_error_if()
$(error-if,...) is expanded to an empty string. Currently, it relies on
eval_clause() returning xstrdup("") when all attempts for expansion fail,
but the correct implementation is to make do_error_if() return xstrdup("").
Marco Elver [Tue, 1 Dec 2020 15:20:18 +0000 (16:20 +0100)]
genksyms: Ignore module scoped _Static_assert()
The C11 _Static_assert() keyword may be used at module scope, and we
need to teach genksyms about it to not abort with an error. We currently
have a growing number of static_assert() (but also direct usage of
_Static_assert()) users at module scope:
More recently, when enabling CONFIG_MODVERSIONS with CONFIG_KCSAN, we
observe a number of warnings:
WARNING: modpost: EXPORT symbol "<..all kcsan symbols..>" [vmlinux] [...]
When running a preprocessed source through 'genksyms -w' a number of
syntax errors point at usage of static_assert()s. In the case of
kernel/kcsan/encoding.h, new static_assert()s had been introduced which
used expressions that appear to cause genksyms to not even be able to
recover from the syntax error gracefully (as it appears was the case
previously).
Therefore, make genksyms ignore all _Static_assert() and the contained
expression. With the fix, usage of _Static_assert() no longer cause
"syntax error" all over the kernel, and the above modpost warnings for
KCSAN are gone, too.
Signed-off-by: Marco Elver <elver@google.com> Acked-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Quentin Perret [Tue, 1 Dec 2020 16:52:22 +0000 (16:52 +0000)]
modpost: turn static exports into error
Using EXPORT_SYMBOL*() on static functions is fundamentally wrong.
Modpost currently reports that as a warning, but clearly this is not a
pattern we should allow, and all in-tree occurences should have been
fixed by now. So, promote the warn() message to error() to make sure
this never happens again.
Masahiro Yamada [Tue, 1 Dec 2020 10:34:15 +0000 (19:34 +0900)]
modpost: refactor error handling and clarify error/fatal difference
We have 3 log functions. fatal() is special because it lets modpost bail
out immediately. The difference between warn() and error() is the only
prefix parts ("WARNING:" vs "ERROR:").
In my understanding, the expected handling of error() is to propagate
the return code of the function to the exit code of modpost, as
check_exports() etc. already does. This is a good manner in general
because we should display as many error messages as possible in a
single run of modpost.
What is annoying about fatal() is that it kills modpost at the first
error. People would need to run Kbuild again and again until they fix
all errors.
But, unfortunately, people tend to do:
"This case should not be allowed. Let's replace warn() with fatal()."
One of the reasons is probably it is tedious to manually hoist the error
code to the main() function.
This commit refactors error() so any single call for it automatically
makes modpost return the error code.
I also added comments in modpost.h for warn(), error(), and fatal().
Please use fatal() only when you have a strong reason to do so.
For example:
- Memory shortage (i.e. malloc() etc. has failed)
- The ELF file is broken, and there is no point to continue parsing
- Something really odd has happened
Masahiro Yamada [Tue, 1 Dec 2020 10:34:14 +0000 (19:34 +0900)]
modpost: rename merror() to error()
The log function names, warn(), merror(), fatal() are inconsistent.
Commit 2a11665945d5 ("kbuild: distinguish between errors and warnings
in modpost") intentionally chose merror() to avoid the conflict with
the library function error(). See man page of error(3).
But, we are already causing the conflict with warn() because it is also
a library function. See man page of warn(3). err() would be a problem
for the same reason.
The common technique to work around name conflicts is to use macros.
For example:
/* in a header */
#define error(fmt, ...) __error(fmt, ##__VA_ARGS__)
#define warn(fmt, ...) __warn(fmt, ##__VA_ARGS__)
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