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arch/riscv: vdso: remove CFI landing pad from rt_sigreturn

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When CONFIG_RISCV_USER_CFI is enabled, the CFI version of the vDSO, has
a CFI landing pad instruction at the start of __vdso_rt_sigreturn. This
breaks libgcc's unwinding code which matches on the first two
instructions. Other unwinders that rely on similar instruction matching
may also be affected.

Since __vdso_rt_sigreturn is reached as part of signal-return handling
rather than via an indirect call/jump from userspace, it does not need a
CFI landing pad. Remove it and restore the instruction sequence expected
by existing unwinding code.

This matches what was done on arm64 in commit 9a96428557 ("arm64:
vdso: Don't prefix sigreturn trampoline with a BTI C instruction") for a
similar issue.

Cc: stable@vger.kernel.org
Fixes: 37f57bd3fa ("arch/riscv: compile vdso with landing pad and shadow stack note")
Co-authored-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://patch.msgid.link/20260623204058.498120-1-aurelien@aurel32.net
[pjw@kernel.org: fixed comment style]
Signed-off-by: Paul Walmsley <pjw@kernel.org>
This commit is contained in:
Aurelien Jarno 2026-06-23 22:40:57 +02:00 committed by Paul Walmsley
parent ad6dcfa023
commit e4bf6eb4c7
1 changed files with 9 additions and 1 deletions
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10
arch/riscv/kernel/vdso/rt_sigreturn.S
View File

@ -7,11 +7,19 @@
#include <asm/unistd.h>
#include <asm/assembler.h>
/*
* WARNING: Do NOT add a CFI landing pad at the start of this function.
* Unwinders such as libgcc identify the sigreturn trampoline by matching the
* instruction sequence. Adding a landing pad here would break unwinding from
* signal handlers.
*
* This trampoline is used only for signal return and not via an indirect
* call/jump from userspace, so adding CFI landing pad is unnecessary.
*/
.text
SYM_FUNC_START(__vdso_rt_sigreturn)
.cfi_startproc
.cfi_signal_frame
vdso_lpad
li a7, __NR_rt_sigreturn
ecall
.cfi_endproc