Re: [PATCH] arch/riscv: vdso: remove CFI landing pad from rt_sigreturn

From: Aurelien Jarno <aurelien@aurel32.net>
To: Paul Walmsley <pjw@kernel.org>
Cc: Joel Stanley <joel@jms.id.au>,
	linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>, Jim Shu <jim.shu@sifive.com>,
	Zong Li <zong.li@sifive.com>, Deepak Gupta <debug@rivosinc.com>,
	"open list:RISC-V ARCHITECTURE" <linux-riscv@lists.infradead.org>
Subject: Re: [PATCH] arch/riscv: vdso: remove CFI landing pad from rt_sigreturn
Date: Tue, 14 Jul 2026 15:35:24 +0200	[thread overview]
Message-ID: <alY7HFcSYkXh97Vy@aurel32.net> (raw)
In-Reply-To: <CACPK8XcJZzynnofpLHsPAD6Lbbjf9=soj+nFhU3ey=3yT2056w@mail.gmail.com>

Hi Paul,

On 2026-06-29 17:08, Joel Stanley wrote:
> On Fri, 26 Jun 2026 at 03:33, Paul Walmsley <pjw@kernel.org> wrote:
> >
> > Hi Joel,
> >
> > On Tue, 23 Jun 2026, Aurelien Jarno wrote:
> >
> > > 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 9a964285572b ("arm64:
> > > vdso: Don't prefix sigreturn trampoline with a BTI C instruction") for a
> > > similar issue.
> > >
> > > Fixes: 37f57bd3faea ("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>
> >
> > I'd like to take this one.   But since you're listed as the co-author, I
> > probably need your Signed-off-by: as well.  Care to reply with it?
> 
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> 
> Thanks Aurelien for working with me on this one. I saw CFI was
> disabled in the debian kernel config and wondered why (failing glibc
> backtrace tests with CFI enabled), and we got to the bottom of it.
> 
> This one should go to stable IMO.

Now that Joel answered with a Signed-off-by, would it be possible to get 
this merged for 7.2?

Thanks
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                     http://aurel32.net

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