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authorMark Rutland <mark.rutland@arm.com>2021-10-19 17:02:08 +0100
committerWill Deacon <will@kernel.org>2021-10-21 10:45:21 +0100
commit4012e0e22739eef92499171957145a60445c0b60 (patch)
treebc9519a9e83a0c4e73357c71152b03e59df1a207 /arch/arm64/lib
parent35d67794b88283337e0d311a4dbacc42d07a12a5 (diff)
downloadlinux-4012e0e22739eef92499171957145a60445c0b60.tar.bz2
arm64: lib: __arch_copy_from_user(): fold fixups into body
Like other functions, __arch_copy_from_user() places its exception fixups in the `.fixup` section without any clear association with __arch_copy_from_user() itself. If we backtrace the fixup code, it will be symbolized as an offset from the nearest prior symbol, which happens to be `__entry_tramp_text_end`. Further, since the PC adjustment for the fixup is akin to a direct branch rather than a function call, __arch_copy_from_user() itself will be missing from the backtrace. This is confusing and hinders debugging. In general this pattern will also be problematic for CONFIG_LIVEPATCH, since fixups often return to their associated function, but this isn't accurately captured in the stacktrace. To solve these issues for assembly functions, we must move fixups into the body of the functions themselves, after the usual fast-path returns. This patch does so for __arch_copy_from_user(). Inline assembly will be dealt with in subsequent patches. Other than the improved backtracing, there should be no functional change as a result of this patch. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Robin Murphy <robin.murphy@arm.com> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Mark Brown <broonie@kernel.org> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20211019160219.5202-3-mark.rutland@arm.com Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/lib')
-rw-r--r--arch/arm64/lib/copy_from_user.S8
1 files changed, 3 insertions, 5 deletions
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 2cf999e41d30..34e317907524 100644
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -60,11 +60,8 @@ SYM_FUNC_START(__arch_copy_from_user)
#include "copy_template.S"
mov x0, #0 // Nothing to copy
ret
-SYM_FUNC_END(__arch_copy_from_user)
-EXPORT_SYMBOL(__arch_copy_from_user)
- .section .fixup,"ax"
- .align 2
+ // Exception fixups
9997: cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
@@ -72,4 +69,5 @@ USER(9998f, ldtrb tmp1w, [srcin])
strb tmp1w, [dst], #1
9998: sub x0, end, dst // bytes not copied
ret
- .previous
+SYM_FUNC_END(__arch_copy_from_user)
+EXPORT_SYMBOL(__arch_copy_from_user)