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

From: Paul Walmsley <pjw@kernel.org>
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: Paul Walmsley <pjw@kernel.org>, 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 19:37:01 -0600 (MDT)	[thread overview]
Message-ID: <eb8fd632-ca2c-9b65-209c-ce2294929cb9@kernel.org> (raw)
In-Reply-To: <alY7HFcSYkXh97Vy@aurel32.net>

Hi Aurelien, Joel,

On Tue, 14 Jul 2026, Aurelien Jarno wrote:
> On 2026-06-29 17:08, Joel Stanley wrote:
> > On Fri, 26 Jun 2026 at 03:33, Paul Walmsley <pjw@kernel.org> wrote:
> > > 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?

Of course; thank you for the reminder.  Thanks for the patch and the 
S-o-b, queued for v7.2-rc with a cc: to stable@vger.

- Paul

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