linux-kernel - Re: [PATCH] objtool/x86: Fixup frame-pointer vs rethunk

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Date:   Wed, 16 Aug 2023 15:22:30 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org
Subject: Re: [PATCH] objtool/x86: Fixup frame-pointer vs rethunk

On Thu, Aug 17, 2023 at 12:08:40AM +0200, Peter Zijlstra wrote:
> On Wed, Aug 16, 2023 at 01:31:52PM -0700, Josh Poimboeuf wrote:
> > On Wed, Aug 16, 2023 at 01:59:21PM +0200, Peter Zijlstra wrote:
> > > Turns out I forgot to build with FRAME_POINTER=y, that still gives:
> > > 
> > > vmlinux.o: warning: objtool: srso_untrain_ret+0xd: call without frame pointer save/setup
> > > 
> > > the below seems to cure this.
> > 
> > LGTM
> 
> OK, with Changelog below.
> 
> ---
> Subject: objtool/x86: Fixup frame-pointer vs rethunk
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed, 16 Aug 2023 13:59:21 +0200
> 
> For stack-validation of a frame-pointer build, objtool validates that
> every CALL instructions is preceded by a frame-setup. The new SRSO
> return thunks violate this with their RSB stuffing trickery.
> 
> Extend the __fentry__ exception to also cover the embedded_insn case
> used for this. This cures:
> 
> vmlinux.o: warning: objtool: srso_untrain_ret+0xd: call without frame pointer save/setup
> 
> Fixes: 4ae68b26c3ab ("objtool/x86: Fix SRSO mess")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>

-- 
Josh