From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: alexandru.elisei@arm.com, andrii@kernel.org, ardb@kernel.org,
ast@kernel.org, broonie@kernel.org, catalin.marinas@arm.com,
daniel@iogearbox.net, dvyukov@google.com, james.morse@arm.com,
jean-philippe@linaro.org, jpoimboe@redhat.com,
mark.rutland@arm.com, maz@kernel.org, peterz@infradead.org,
robin.murphy@arm.com, suzuki.poulose@arm.com, will@kernel.org
Subject: [PATCH 02/13] arm64: lib: __arch_copy_from_user(): fold fixups into body
Date: Wed, 13 Oct 2021 12:00:48 +0100 [thread overview]
Message-ID: <20211013110059.10324-3-mark.rutland@arm.com> (raw)
In-Reply-To: <20211013110059.10324-1-mark.rutland@arm.com>
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>
Cc: 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: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
---
arch/arm64/lib/copy_from_user.S | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 2cf999e41d30..f50ba67a73b4 100644
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -60,11 +60,7 @@ 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
9997: cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
@@ -72,4 +68,5 @@ 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)
--
2.11.0
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next prev parent reply other threads:[~2021-10-13 12:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-13 11:00 [PATCH 00/13] arm64: extable: remove anonymous out-of-line fixups Mark Rutland
2021-10-13 11:00 ` [PATCH 01/13] arm64: lib: __arch_clear_user(): fold fixups into body Mark Rutland
2021-10-13 19:55 ` Robin Murphy
2021-10-14 11:09 ` Mark Rutland
2021-10-13 11:00 ` Mark Rutland [this message]
2021-10-13 11:00 ` [PATCH 03/13] arm64: lib: __arch_copy_to_user(): " Mark Rutland
2021-10-13 11:00 ` [PATCH 04/13] arm64: kvm: use kvm_exception_table_entry Mark Rutland
2021-10-13 11:00 ` [PATCH 05/13] arm64: factor out GPR numbering helpers Mark Rutland
2021-10-13 11:00 ` [PATCH 06/13] arm64: gpr-num: support W registers Mark Rutland
2021-10-13 11:00 ` [PATCH 07/13] arm64: extable: consolidate definitions Mark Rutland
2021-10-13 11:00 ` [PATCH 08/13] arm64: extable: make fixup_exception() return bool Mark Rutland
2021-10-13 11:00 ` [PATCH 09/13] arm64: extable: use `ex` for `exception_table_entry` Mark Rutland
2021-10-13 11:00 ` [PATCH 10/13] arm64: extable: add `type` and `data` fields Mark Rutland
2021-10-19 11:29 ` Will Deacon
2021-10-19 11:50 ` Mark Rutland
2021-10-19 12:05 ` Will Deacon
2021-10-19 12:12 ` Ard Biesheuvel
2021-10-19 13:01 ` Mark Rutland
2021-10-13 11:00 ` [PATCH 11/13] arm64: extable: add a dedicated uaccess handler Mark Rutland
2021-10-13 11:00 ` [PATCH 12/13] arm64: extable: add load_unaligned_zeropad() handler Mark Rutland
2021-10-13 11:00 ` [PATCH 13/13] arm64: vmlinux.lds.S: remove `.fixup` section Mark Rutland
2021-10-17 13:50 ` [PATCH 00/13] arm64: extable: remove anonymous out-of-line fixups Ard Biesheuvel
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