linux-kernel - [PATCH] arm64: Fix off-by-one vdso trampoline return value

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Message-Id: <20201112001422.340449-1-willmcvicker@google.com>
Date:   Thu, 12 Nov 2020 00:14:22 +0000
From:   Will McVicker <willmcvicker@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrei Vagin <avagin@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, kernel-team@...roid.com,
        Will McVicker <willmcvicker@...gle.com>
Subject: [PATCH] arm64: Fix off-by-one vdso trampoline return value

Depending on your host nm version, the generated header
`include/generated/vdso32-offsets.h` may have the bottom bit set for the
thumb vdso offset addresses (as observed when using llvm-nm). This
results in an additional +1 for thumb vdso trampoline return values
since compat_setup_return() already includes `vdso_trampoline + thumb`.
As a result, I see a SIGBUS error when running the LTP test
syscalls.rt_sigaction01. To fix this, let's clear the bottom bit of the
vdso_offset in the VDSO_SYMBOL macro.

Test: LTP test syscalls.rt_sigaction01
Fixes: f01703b3d2e6 ("arm64: compat: Get sigreturn trampolines from vDSO")
Signed-off-by: Will McVicker <willmcvicker@...gle.com>
---
 arch/arm64/include/asm/vdso.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
index f99dcb94b438..a7384379e8e1 100644
--- a/arch/arm64/include/asm/vdso.h
+++ b/arch/arm64/include/asm/vdso.h
@@ -23,7 +23,7 @@
 
 #define VDSO_SYMBOL(base, name)						   \
 ({									   \
-	(void *)(vdso_offset_##name - VDSO_LBASE + (unsigned long)(base)); \
+	(void *)((vdso_offset_##name & ~1UL) - VDSO_LBASE + (unsigned long)(base)); \
 })
 
 #endif /* !__ASSEMBLY__ */
-- 
2.29.2.299.gdc1121823c-goog