linux-kernel - Re: [PATCH -next v2] x86: Prevent KASAN false positive warnings in __show

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Message-ID: <xlaeuraw7mupek3fp62o7ahp5viusp6uo36jadtuidpwwkmy6a@5pzmlcxtb2ro>
Date: Fri, 29 Aug 2025 14:01:59 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Tengda Wu <wutengda@...weicloud.com>
Cc: x86@...nel.org, Andrey Ryabinin <ryabinin.a.a@...il.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, 
	Borislav Petkov <bp@...en8.de>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v2] x86: Prevent KASAN false positive warnings in
 __show_regs

On Fri, Aug 29, 2025 at 09:47:44AM +0000, Tengda Wu wrote:
>  static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
>  				  bool partial, const char *log_lvl)
>  {
> +	bool kasan_disabled = false;
> +
> +	/*
> +	 * When 'regs' resides in another task's stack space, KASAN should be
> +	 * disabled to prevent false positives during 'regs->' operation, as
> +	 * the 'regs' contents may change concurrently with task execution.
> +	 */
> +	if (!object_is_on_stack(regs)) {
> +		kasan_disable_current();
> +		kasan_disabled = true;
> +	}

I don't think this is right.  object_is_on_stack() only checks current's
*task* stack.  However the regs might be on a different stack used by
current (e.g., exception stack).  In which case there's no need to
disable KASAN.

What really determines the KASAN-safety is whether it's the current task
or not.

-- 
Josh