linux-kernel - Re: [PATCH v12 6/8] x86/traps: Communicate a LASS violation in #GP message

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Message-ID: <20251118112338.GDaRxXOqONunUHGgV6@fat_crate.local>
Date: Tue, 18 Nov 2025 12:23:38 +0100
From: Borislav Petkov <bp@...en8.de>
To: Sohil Mehta <sohil.mehta@...el.com>
Cc: x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Jonathan Corbet <corbet@....net>,
	"H . Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	"Kirill A . Shutemov" <kas@...nel.org>, Xin Li <xin@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Sean Christopherson <seanjc@...gle.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Kees Cook <kees@...nel.org>, Tony Luck <tony.luck@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH v12 6/8] x86/traps: Communicate a LASS violation in #GP
 message

On Mon, Nov 17, 2025 at 11:45:38AM -0800, Sohil Mehta wrote:
> Would this update to the comment help clarify?

Yap, that LGTM.

> 	/*
> 	 * A NULL pointer dereference usually causes a #PF. However, it
> 	 * can result in a #GP when LASS is active. Provide the same
> 	 * hint in the rare case that the condition is hit without LASS.
> 	 */
> 	if (*addr < PAGE_SIZE)
> 		return GP_NULL_POINTER;
> 
> 	/*
> 	 * Assume that LASS caused the exception, because the address is
> 	 * canonical and in the user half.
> 	 */
> 	if (cpu_feature_enabled(X86_FEATURE_LASS))
> 		return GP_LASS_VIOLATION;

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette