From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Will Deacon <will@kernel.org>,
Tamas Zsoldos <tamas.zsoldos@arm.com>,
Mark Brown <broonie@kernel.org>,
kernel-team@android.com, Dave Martin <dave.martin@arm.com>,
Daniel Kiss <daniel.kiss@arm.com>
Subject: [PATCH v2 1/2] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction
Date: Tue, 19 May 2020 17:28:20 +0100 [thread overview]
Message-ID: <20200519162821.16857-2-will@kernel.org> (raw)
In-Reply-To: <20200519162821.16857-1-will@kernel.org>
For better or worse, GDB relies on the exact instruction sequence in the
VDSO sigreturn trampoline in order to unwind from signals correctly.
Commit c91db232da48 ("arm64: vdso: Convert to modern assembler annotations")
unfortunately added a BTI C instruction to the start of __kernel_rt_sigreturn,
which breaks this check. Thankfully, it's also not required, since the
trampoline is called from a RET instruction when returning from the signal
handler
Remove the unnecessary BTI C instruction from __kernel_rt_sigreturn,
and do the same for the 32-bit VDSO as well for good measure.
Cc: Dave Martin <dave.martin@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Daniel Kiss <daniel.kiss@arm.com>
Cc: Tamas Zsoldos <tamas.zsoldos@arm.com>
Fixes: c91db232da48 ("arm64: vdso: Convert to modern assembler annotations")
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/kernel/vdso/sigreturn.S | 11 +++++++++--
arch/arm64/kernel/vdso32/sigreturn.S | 16 ++++++++--------
2 files changed, 17 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S
index 3fb13b81f780..0c921130002a 100644
--- a/arch/arm64/kernel/vdso/sigreturn.S
+++ b/arch/arm64/kernel/vdso/sigreturn.S
@@ -15,7 +15,14 @@
.text
nop
-SYM_FUNC_START(__kernel_rt_sigreturn)
+/*
+ * GDB relies on being able to identify the sigreturn instruction sequence to
+ * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START()
+ * here, as it will emit a BTI C instruction and break the unwinder. Thankfully,
+ * this function is only ever called from a RET and so omitting the landing pad
+ * is perfectly fine.
+ */
+SYM_CODE_START(__kernel_rt_sigreturn)
.cfi_startproc
.cfi_signal_frame
.cfi_def_cfa x29, 0
@@ -24,6 +31,6 @@ SYM_FUNC_START(__kernel_rt_sigreturn)
mov x8, #__NR_rt_sigreturn
svc #0
.cfi_endproc
-SYM_FUNC_END(__kernel_rt_sigreturn)
+SYM_CODE_END(__kernel_rt_sigreturn)
emit_aarch64_feature_1_and
diff --git a/arch/arm64/kernel/vdso32/sigreturn.S b/arch/arm64/kernel/vdso32/sigreturn.S
index 620524969696..b36d4e2267a3 100644
--- a/arch/arm64/kernel/vdso32/sigreturn.S
+++ b/arch/arm64/kernel/vdso32/sigreturn.S
@@ -17,39 +17,39 @@
.save {r0-r15}
.pad #COMPAT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_sigreturn_arm)
+SYM_CODE_START(__kernel_sigreturn_arm)
mov r7, #__NR_compat_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_sigreturn_arm)
+SYM_CODE_END(__kernel_sigreturn_arm)
.fnstart
.save {r0-r15}
.pad #COMPAT_RT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_rt_sigreturn_arm)
+SYM_CODE_START(__kernel_rt_sigreturn_arm)
mov r7, #__NR_compat_rt_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_rt_sigreturn_arm)
+SYM_CODE_END(__kernel_rt_sigreturn_arm)
.thumb
.fnstart
.save {r0-r15}
.pad #COMPAT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_sigreturn_thumb)
+SYM_CODE_START(__kernel_sigreturn_thumb)
mov r7, #__NR_compat_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_sigreturn_thumb)
+SYM_CODE_END(__kernel_sigreturn_thumb)
.fnstart
.save {r0-r15}
.pad #COMPAT_RT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_rt_sigreturn_thumb)
+SYM_CODE_START(__kernel_rt_sigreturn_thumb)
mov r7, #__NR_compat_rt_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_rt_sigreturn_thumb)
+SYM_CODE_END(__kernel_rt_sigreturn_thumb)
--
2.26.2.761.g0e0b3e54be-goog
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next prev parent reply other threads:[~2020-05-19 16:29 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 16:28 [PATCH v2 0/2] arm64 sigreturn unwinding fixes Will Deacon
2020-05-19 16:28 ` Will Deacon [this message]
2020-05-19 16:33 ` [PATCH v2 1/2] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Mark Brown
2020-05-20 9:33 ` Dave Martin
2020-05-20 9:53 ` Will Deacon
2020-05-19 16:28 ` [PATCH v2 2/2] arm64: vdso: Fix CFI directives in sigreturn trampoline Will Deacon
2020-05-20 9:42 ` Dave Martin
2020-05-20 9:50 ` Will Deacon
2020-05-20 10:27 ` Dave Martin
2020-05-20 10:36 ` Will Deacon
2020-05-20 11:03 ` Dave Martin
2020-05-20 10:48 ` Will Deacon
2020-05-20 11:06 ` Dave Martin
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