kexec_file: make use of purgatory optional

Patch series "kexec_file, x86, powerpc: refactoring for other
architecutres", v2.

This is a preparatory patchset for adding kexec_file support on arm64.

It was originally included in a arm64 patch set[1], but Philipp is also
working on their kexec_file support on s390[2] and some changes are now
conflicting.

So these common parts were extracted and put into a separate patch set
for better integration.  What's more, my original patch#4 was split into
a few small chunks for easier review after Dave's comment.

As such, the resulting code is basically identical with my original, and
the only *visible* differences are:

 - renaming of _kexec_kernel_image_probe() and  _kimage_file_post_load_cleanup()

 - change one of types of arguments at prepare_elf64_headers()

Those, unfortunately, require a couple of trivial changes on the rest
(#1, #6 to #13) of my arm64 kexec_file patch set[1].

Patch #1 allows making a use of purgatory optional, particularly useful
for arm64.

Patch #2 commonalizes arch_kexec_kernel_{image_probe, image_load,
verify_sig}() and arch_kimage_file_post_load_cleanup() across
architectures.

Patches #3-#7 are also intended to generalize parse_elf64_headers(),
along with exclude_mem_range(), to be made best re-use of.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-February/561182.html
[2] http://lkml.iu.edu//hypermail/linux/kernel/1802.1/02596.html

This patch (of 7):

On arm64, crash dump kernel's usable memory is protected by *unmapping*
it from kernel virtual space unlike other architectures where the region
is just made read-only.  It is highly unlikely that the region is
accidentally corrupted and this observation rationalizes that digest
check code can also be dropped from purgatory.  The resulting code is so
simple as it doesn't require a bit ugly re-linking/relocation stuff,
i.e.  arch_kexec_apply_relocations_add().

Please see:

   http://lists.infradead.org/pipermail/linux-arm-kernel/2017-December/545428.html

All that the purgatory does is to shuffle arguments and jump into a new
kernel, while we still need to have some space for a hash value
(purgatory_sha256_digest) which is never checked against.

As such, it doesn't make sense to have trampline code between old kernel
and new kernel on arm64.

This patch introduces a new configuration, ARCH_HAS_KEXEC_PURGATORY, and
allows related code to be compiled in only if necessary.

[takahiro.akashi@linaro.org: fix trivial screwup]
Link: http://lkml.kernel.org/r/20180309093346.GF25863@linaro.org
Link: http://lkml.kernel.org/r/20180306102303.9063-2-takahiro.akashi@linaro.org
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Acked-by: Dave Young <dyoung@redhat.com>
Tested-by: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 73ce5dd076420720822890ab8425632d3632870c..c32a181a7cbbfc30ab9c55d925d89a282857bbf3 100644 (file)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -552,6 +552,9 @@ config KEXEC_FILE
          for kernel and initramfs as opposed to a list of segments as is the
          case for the older kexec call.
 
+config ARCH_HAS_KEXEC_PURGATORY
+       def_bool KEXEC_FILE
+
 config RELOCATABLE
        bool "Build a relocatable kernel"
        depends on PPC64 || (FLATMEM && (44x || FSL_BOOKE))

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index d234cca296dbe045939e7b871a807a6d301af86d..7fe107f5990b195bc84cd8c5cb8a18d18d5fba57 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2008,6 +2008,9 @@ config KEXEC_FILE
          for kernel and initramfs as opposed to list of segments as
          accepted by previous system call.
 
+config ARCH_HAS_KEXEC_PURGATORY
+       def_bool KEXEC_FILE
+
 config KEXEC_VERIFY_SIG
        bool "Verify kernel signature during kexec_file_load() syscall"
        depends on KEXEC_FILE

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index e5bcd94c1efb13db5daa12d7dd188279ea25c1a1..ab1dced677fd8583c60cfe3469031a8ec710e3bb 100644 (file)
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -532,6 +532,9 @@ static int kexec_calculate_store_digests(struct kimage *image)
        struct kexec_sha_region *sha_regions;
        struct purgatory_info *pi = &image->purgatory_info;
 
+       if (!IS_ENABLED(CONFIG_ARCH_HAS_KEXEC_PURGATORY))
+               return 0;
+
        zero_buf = __va(page_to_pfn(ZERO_PAGE(0)) << PAGE_SHIFT);
        zero_buf_sz = PAGE_SIZE;
 
@@ -633,6 +636,7 @@ out:
        return ret;
 }
 
+#ifdef CONFIG_ARCH_HAS_KEXEC_PURGATORY
 /* Actually load purgatory. Lot of code taken from kexec-tools */
 static int __kexec_load_purgatory(struct kimage *image, unsigned long min,
                                  unsigned long max, int top_down)
@@ -1022,3 +1026,4 @@ int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
 
        return 0;
 }
+#endif /* CONFIG_ARCH_HAS_KEXEC_PURGATORY */