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

From: Nick Desaulniers <ndesaulniers@google.com>
To: Will McVicker <willmcvicker@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Andrei Vagin <avagin@gmail.com>,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	kernel-team <kernel-team@android.com>
Subject: Re: [PATCH] arm64: Fix off-by-one vdso trampoline return value
Date: Wed, 11 Nov 2020 17:00:43 -0800	[thread overview]
Message-ID: <CAKwvOdkDG2wt=ZT93GT7r60_qXn=tdW_zWiJ1Gr5JVdRvcU8uw@mail.gmail.com> (raw)
In-Reply-To: <20201112001422.340449-1-willmcvicker@google.com>

On Wed, Nov 11, 2020 at 4:14 PM Will McVicker <willmcvicker@google.com> wrote:
>
> 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

Sorry, the commit message seems to imply a bug in llvm-nm, but I don't
think that's the case.  If it is, please, send us a bugreport.

$ aarch64-linux-gnu-nm arch/arm64/kernel/vdso32/vdso.so.raw | grep thumb
00000968 T __kernel_rt_sigreturn_thumb
00000960 T __kernel_sigreturn_thumb
00000968 t VDSO_compat_rt_sigreturn_thumb
00000960 t VDSO_compat_sigreturn_thumb
$ llvm-nm arch/arm64/kernel/vdso32/vdso.so.raw | grep thumb
00000968 t VDSO_compat_rt_sigreturn_thumb
00000960 t VDSO_compat_sigreturn_thumb
00000968 T __kernel_rt_sigreturn_thumb
00000960 T __kernel_sigreturn_thumb
$ /usr/bin/nm arch/arm64/kernel/vdso32/vdso.so.raw | grep thumb
00000969 T __kernel_rt_sigreturn_thumb
00000961 T __kernel_sigreturn_thumb
00000969 t VDSO_compat_rt_sigreturn_thumb
00000961 t VDSO_compat_sigreturn_thumb
$ /usr/bin/nm --version
GNU nm (GNU Binutils for Debian) 2.35.1

Would you mind amending the commit message to not imply that llvm-nm is broken?

It might be of interest to find out why the host `nm` was invoked,
rather than $(NM)/$(CROSS_COMPILE)nm.

> 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@google.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
>

-- 
Thanks,
~Nick Desaulniers