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>.

This patchset is available here:

https://github.com/xairy/linux/tree/up-kasan-mte-v11

For testing in QEMU hardware tag-based KASAN requires:

1. QEMU built from master [4] (use "-machine virt,mte=on -cpu max" arguments
   to run).
2. GCC version 10.

[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html
[2] https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/enhancing-memory-safety
[3] git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux for-next/mte
[4] https://github.com/qemu/qemu

====== Overview

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:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0116523cfffa62aeb5aa3b85ce7419f3dae0c1b8

===== Tags

Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
This patch (of 41):

Don't mention "GNU General Public License version 2" text explicitly, as
it's already covered by the SPDX-License-Identifier.

Link: https://lkml.kernel.org/r/cover.1606161801.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/6ea9f5f4aa9dbbffa0d0c0a780b37699a4531034.1606161801.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 950fd372a07ecd982603cc5fe896e9e9e821ca36..33d863f55db19f8814ad5f1de126cac8dc34eded 100644 (file)
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -7,11 +7,6 @@
  *
  * Some code borrowed from https://github.com/xairy/kasan-prototype by
  *        Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/export.h>

diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 30c0a5038b5cd4c34e02b183bc07028a078484eb..d341859a1b955d35787f99877c0878d7eb4d8a84 100644 (file)
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -7,11 +7,6 @@
  *
  * Some code borrowed from https://github.com/xairy/kasan-prototype by
  *        Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index a38c7a9e192a6623adeb3720d95579f2c6462b4a..6bb3f66992df43d0ad65ed5a1719361989e8a8c4 100644 (file)
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -7,11 +7,6 @@
  *
  * Some code borrowed from https://github.com/xairy/kasan-prototype by
  *        Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/bitops.h>

diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index fe6be0be1f763c3b58e51c9b5399fe3294cb6120..9ce8cc5b8621f581bd483653514b0bb2e4630c54 100644 (file)
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -4,11 +4,6 @@
  *
  * Copyright (c) 2015 Samsung Electronics Co., Ltd.
  * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/memblock.h>

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 0e3f8494628f64bebd3445484c41ae5555e6f6eb..693b05e2c2aa7a24044282978d531b9095daa896 100644 (file)
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -6,16 +6,6 @@
  * Copyright (C) 2016 Google, Inc.
  *
  * Based on code by Dmitry Chernenkov.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * version 2 as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
- *
  */
 
 #include <linux/gfp.h>

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 5a0102f37171306283ff6275ada33c8f439b4a89..0a2c72ddcdebbfb2cdc2266ab927d0db2009a244 100644 (file)
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -7,11 +7,6 @@
  *
  * Some code borrowed from https://github.com/xairy/kasan-prototype by
  *        Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/bitops.h>

diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index e02a36a51f4296335e678a2baef249d40b2cec39..5c8b08a2571570b098761aafeea9fea00cdd3f9a 100644 (file)
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -4,11 +4,6 @@
  *
  * Copyright (c) 2018 Google, Inc.
  * Author: Andrey Konovalov <andreyknvl@google.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
index bee43717d6f0b3c048d3aa761a9c1ea750bca545..5f183501b8710846fee60503ad803015a4030005 100644 (file)
--- a/mm/kasan/tags_report.c
+++ b/mm/kasan/tags_report.c
@@ -7,11 +7,6 @@
  *
  * Some code borrowed from https://github.com/xairy/kasan-prototype by
  *        Andrey Konovalov <andreyknvl@gmail.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/bitops.h>