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 v2 01/13] arm64: lib: __arch_clear_user(): fold fixups into body
Date: Tue, 19 Oct 2021 17:02:07 +0100 [thread overview]
Message-ID: <20211019160219.5202-2-mark.rutland@arm.com> (raw)
In-Reply-To: <20211019160219.5202-1-mark.rutland@arm.com>
Like other functions, __arch_clear_user() places its exception fixups in
the `.fixup` section without any clear association with
__arch_clear_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_clear_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_clear_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>
---
arch/arm64/lib/clear_user.S | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index a7efb2ad2a1c..2827fddc33f8 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -45,13 +45,11 @@ USER(9f, sttrh wzr, [x0])
USER(7f, sttrb wzr, [x2, #-1])
5: mov x0, #0
ret
-SYM_FUNC_END(__arch_clear_user)
-EXPORT_SYMBOL(__arch_clear_user)
- .section .fixup,"ax"
- .align 2
+ // Exception fixups
7: sub x0, x2, #5 // Adjust for faulting on the final byte...
8: add x0, x0, #4 // ...or the second word of the 4-7 byte case
9: sub x0, x2, x0
ret
- .previous
+SYM_FUNC_END(__arch_clear_user)
+EXPORT_SYMBOL(__arch_clear_user)
--
2.11.0
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next prev parent reply other threads:[~2021-10-19 16:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 16:02 [PATCH v2 00/13] arm64: extable: remove anonymous out-of-line fixups Mark Rutland
2021-10-19 16:02 ` Mark Rutland [this message]
2021-10-19 16:02 ` [PATCH v2 02/13] arm64: lib: __arch_copy_from_user(): fold fixups into body Mark Rutland
2021-10-19 16:02 ` [PATCH v2 03/13] arm64: lib: __arch_copy_to_user(): " Mark Rutland
2021-10-19 16:02 ` [PATCH v2 04/13] arm64: kvm: use kvm_exception_table_entry Mark Rutland
2021-10-21 9:09 ` Marc Zyngier
2021-10-19 16:02 ` [PATCH v2 05/13] arm64: factor out GPR numbering helpers Mark Rutland
2021-10-19 16:02 ` [PATCH v2 06/13] arm64: gpr-num: support W registers Mark Rutland
2021-10-19 16:02 ` [PATCH v2 07/13] arm64: extable: consolidate definitions Mark Rutland
2021-10-19 16:02 ` [PATCH v2 08/13] arm64: extable: make fixup_exception() return bool Mark Rutland
2021-10-19 16:02 ` [PATCH v2 09/13] arm64: extable: use `ex` for `exception_table_entry` Mark Rutland
2021-10-19 16:02 ` [PATCH v2 10/13] arm64: extable: add `type` and `data` fields Mark Rutland
2021-10-19 16:02 ` [PATCH v2 11/13] arm64: extable: add a dedicated uaccess handler Mark Rutland
2021-10-19 16:02 ` [PATCH v2 12/13] arm64: extable: add load_unaligned_zeropad() handler Mark Rutland
2021-10-19 16:02 ` [PATCH v2 13/13] arm64: vmlinux.lds.S: remove `.fixup` section Mark Rutland
2021-10-21 10:05 ` [PATCH v2 00/13] arm64: extable: remove anonymous out-of-line fixups Will Deacon
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