From 139f9ab73d60cf76d770841a019c5284fcf26c74 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Tue, 19 Oct 2021 17:02:09 +0100 Subject: [PATCH] arm64: lib: __arch_copy_to_user(): fold fixups into body Like other functions, __arch_copy_to_user() places its exception fixups in the `.fixup` section without any clear association with __arch_copy_to_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_to_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_to_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 Acked-by: Robin Murphy Reviewed-by: Ard Biesheuvel Cc: Catalin Marinas Cc: James Morse Cc: Mark Brown Cc: Will Deacon Link: https://lore.kernel.org/r/20211019160219.5202-4-mark.rutland@arm.com Signed-off-by: Will Deacon --- arch/arm64/lib/copy_to_user.S | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S index 9f380eecf653..802231772608 100644 --- a/arch/arm64/lib/copy_to_user.S +++ b/arch/arm64/lib/copy_to_user.S @@ -59,11 +59,8 @@ SYM_FUNC_START(__arch_copy_to_user) #include "copy_template.S" mov x0, #0 ret -SYM_FUNC_END(__arch_copy_to_user) -EXPORT_SYMBOL(__arch_copy_to_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, sttrb tmp1w, [dst]) add dst, dst, #1 9998: sub x0, end, dst // bytes not copied ret - .previous +SYM_FUNC_END(__arch_copy_to_user) +EXPORT_SYMBOL(__arch_copy_to_user) -- 2.42.0