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

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Date:   Wed, 11 Nov 2020 18:14:15 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Will McVicker <willmcvicker@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrei Vagin <avagin@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH] arm64: Fix off-by-one vdso trampoline return value

On Wed, Nov 11, 2020 at 5:00 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Wed, Nov 11, 2020 at 4:14 PM Will McVicker <willmcvicker@...gle.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?

Testing another set of configs:

$ aarch64-linux-android-nm arch/arm64/kernel/vdso32/vdso.so.dbg | grep thumb
00000950 T __kernel_rt_sigreturn_thumb
00000948 T __kernel_sigreturn_thumb
00000951 t VDSO_compat_rt_sigreturn_thumb
00000949 t VDSO_compat_sigreturn_thumb
$ /path/to/older/aarch64-linux-gnu-nm
arch/arm64/kernel/vdso32/vdso.so.dbg | grep thumb
00000950 T __kernel_rt_sigreturn_thumb
00000948 T __kernel_sigreturn_thumb
00000951 t VDSO_compat_rt_sigreturn_thumb
00000949 t VDSO_compat_sigreturn_thumb
$ /usr/bin/nm out/android-4.19-stable/common/arch/arm64/kernel/vdso32/vdso.so.dbg
| grep thumb
00000951 T __kernel_rt_sigreturn_thumb
00000949 T __kernel_sigreturn_thumb
00000951 t VDSO_compat_rt_sigreturn_thumb
00000949 t VDSO_compat_sigreturn_thumb
$ llvm-nm out/android-4.19-stable/common/arch/arm64/kernel/vdso32/vdso.so.dbg
| grep thumb
00000951 t VDSO_compat_rt_sigreturn_thumb
00000949 t VDSO_compat_sigreturn_thumb
00000950 T __kernel_rt_sigreturn_thumb
00000948 T __kernel_sigreturn_thumb

(That llvm-nm sorts the output makes this trickier to follow). But
shows that only host GNU `nm` differs.

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

Possibly commit 7b7891c7bdfd ("arm64: vdso32: Fix '--prefix=' value
for newer versions of clang") missing from your tree, but I fail to
see how that would mess up or invoke the incorrect $(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@...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
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers