linux-kernel - Re: [PATCH v11 7/9] x86/traps: Communicate a LASS violation in #GP message

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Message-ID: <76e8411b-e5ff-4c01-b63c-ef60e29388a3@intel.com>
Date: Fri, 31 Oct 2025 12:59:04 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, <x86@...nel.org>, Dave Hansen
	<dave.hansen@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, "Ingo
 Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
CC: 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 v11 7/9] x86/traps: Communicate a LASS violation in #GP
 message

On 10/31/2025 10:16 AM, Dave Hansen wrote:
> On 10/29/25 14:03, Sohil Mehta wrote:
>> To make the transition easier, enhance the #GP Oops message to include a
>> hint about LASS violations. Also, add a special hint for kernel NULL
>> pointer dereferences to match with the existing #PF message.
> 
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> This also reminds me... Are there tests for this somewhere? How did you
> test all these new messages?

I have some very simple kernel modules that access invalid user memory
and generate these faults. I configure the kernel not to panic/reboot.
But, I have been running them manually.

Invalid accesses from the kernel generate:
#PF (without LASS):
  BUG: kernel NULL pointer dereference, address: 0000000000000000
  BUG: unable to handle page fault for address: 0000000000100000

#GP (with LASS):
  Oops: general protection fault, kernel NULL pointer dereference 0x0: 0000
  Oops: general protection fault, probably LASS violation for address
0x100000: 0000

For testing user SIGSEGVs, the Vsyscall tests have been sufficient to
cover all scenarios.

Were you looking for anything specific? I can clean them up and post
them if required.