linux-kernel - Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching kernel alternatives

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Message-ID: <iebitnv533feb5axuf4jtgetajwmwgvaocmanw6swejv5cfxrd@numffxr7uj4p>
Date: Wed, 9 Jul 2025 12:35:42 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Sohil Mehta <sohil.mehta@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
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	"Paul E. McKenney" <paulmck@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Xiongwei Song <xiongwei.song@...driver.com>, Xin Li <xin3.li@...el.com>, 
	"Mike Rapoport (IBM)" <rppt@...nel.org>, Brijesh Singh <brijesh.singh@....com>, 
	Michael Roth <michael.roth@....com>, Tony Luck <tony.luck@...el.com>, 
	Alexey Kardashevskiy <aik@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
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	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching
 kernel alternatives

On Tue, Jul 08, 2025 at 06:08:18PM -0700, Sohil Mehta wrote:
> On 7/7/2025 1:03 AM, Kirill A. Shutemov wrote:
> > From: Sohil Mehta <sohil.mehta@...el.com>
> > 
> > For patching, the kernel initializes a temporary mm area in the lower
> > half of the address range. See commit 4fc19708b165 ("x86/alternatives:
> > Initialize temporary mm for patching").
> > 
> > Disable LASS enforcement during patching to avoid triggering a #GP
> > fault.
> > 
> > The objtool warns due to a call to a non-allowed function that exists
> > outside of the stac/clac guard, or references to any function with a
> > dynamic function pointer inside the guard. See the Objtool warnings
> > section #9 in the document tools/objtool/Documentation/objtool.txt.
> > 
> > Considering that patching is usually small, replace the memcpy() and
> > memset() functions in the text poking functions with their open coded
> > versions.
> > 
> > Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>
> > Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> Kirill, it might be worth adding your co-developed-by tag. The patch has
> more changes than I can claim credit for.

Okay. Will do.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov