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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251117144840.GIaRs1yNEYjdNF0SHu@fat_crate.local>
Date: Mon, 17 Nov 2025 15:48:40 +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 Thu, Nov 13, 2025 at 02:42:02PM -0800, Sohil Mehta wrote:
> +	/*
> +	 * If LASS is active, a NULL pointer dereference generates a #GP
> +	 * instead of a #PF.
> +	 */

I'm having trouble matching the comment...

> +	if (*addr < PAGE_SIZE)

... to the conditional.

Aaaha:

"With LASS active, any invalid access to user memory (including the first page
frame) would be..."

Why is the first page frame special to justify a special check?

I must be missing something obvious here...

Thx.

-- 
Regards/Gruss,
    Boris.

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