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Date:   Thu, 3 Nov 2022 12:18:14 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexander Potapenko <glider@google.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org
Subject: Re: [PATCH 5/5] x86/traps: avoid KMSAN bugs originating from
 handle_bug()
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References: <20221102110611.1085175-1-glider@google.com>
 <20221102110611.1085175-5-glider@google.com>
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On Wed, Nov 02, 2022 at 12:06:11PM +0100, Alexander Potapenko wrote:

> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 178015a820f08..d3fdec706f1d2 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -15,6 +15,7 @@
>  #include <linux/context_tracking.h>
>  #include <linux/interrupt.h>
>  #include <linux/kallsyms.h>
> +#include <linux/kmsan.h>
>  #include <linux/spinlock.h>
>  #include <linux/kprobes.h>
>  #include <linux/uaccess.h>
> @@ -301,6 +302,12 @@ static noinstr bool handle_bug(struct pt_regs *regs)
>  {
>  	bool handled = false;
>  
> +	/*
> +	 * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
> +	 * is a rare case that uses @regs without passing them to
> +	 * irqentry_enter().
> +	 */
> +	kmsan_unpoison_entry_regs(regs);
>  	if (!is_valid_bugaddr(regs->ip))
>  		return handled;
>  

Should we place this kmsan_unpoison_entry_regs() after the
instrumentation_begin() ?