linux-kernel - Re: [PATCH v2] x86/traps: avoid KMSAN bugs originating from handle

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Message-ID: <Y2PRGeTIZU3T3IqX@hirez.programming.kicks-ass.net>
Date:   Thu, 3 Nov 2022 15:32:57 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: Re: [PATCH v2] x86/traps: avoid KMSAN bugs originating from
 handle_bug()

On Thu, Nov 03, 2022 at 02:45:15PM +0100, Alexander Potapenko wrote:
> There is a case in exc_invalid_op handler that is executed outside the
> irqentry_enter()/irqentry_exit() region when an UD2 instruction is used
> to encode a call to __warn().
> 
> In that case the `struct pt_regs` passed to the interrupt handler is
> never unpoisoned by KMSAN (this is normally done in irqentry_enter()),
> which leads to false positives inside handle_bug().
> 
> Use kmsan_unpoison_entry_regs() to explicitly unpoison those registers
> before using them.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: x86@...nel.org
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> 
> ---
> 
> v2:
>  - move the call to kmsan_unpoison_entry_regs() after the
>    instrumentation_begin(), as suggested by Peter Zijlstra

Thanks!

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>