linux-kernel - Re: [PATCH v2] x86/static_call: Fix __static_call

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Message-ID: <20230816210249.7jk6wmxatfz7riwr@treble>
Date:   Wed, 16 Aug 2023 14:02:49 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, baron@...mai.com, rostedt@...dmis.org,
        ardb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        linux-kernel@...r.kernel.org, christian@...cart.de,
        song@...nel.org, mcgrof@...nel.org
Subject: Re: [PATCH v2] x86/static_call: Fix __static_call_fixup()

On Wed, Aug 16, 2023 at 12:44:19PM +0200, Peter Zijlstra wrote:
> 
> Christian reported spurious module load crashes after some of Song's
> module memory layout patches.
> 
> Turns out that if the very last instruction on the very last page of the
> module is a 'JMP __x86_return_thunk' then __static_call_fixup() will
> trip a fault and die.
> 
> And while the module rework made this slightly more likely to happen,
> it's always been possible.
> 
> Fixes: ee88d363d156 ("x86,static_call: Use alternative RET encoding")
> Reported-by: Christian Bricart <christian@...cart.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

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

-- 
Josh