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

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Message-ID: <53b8d516-5d19-4b3b-b7fa-99f1066f79fe@intel.com>
Date: Tue, 8 Jul 2025 18:08:18 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andy Lutomirski
	<luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
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	<brijesh.singh@....com>, Michael Roth <michael.roth@....com>, Tony Luck
	<tony.luck@...el.com>, Alexey Kardashevskiy <aik@....com>, Alexander Shishkin
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Subject: Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching
 kernel alternatives

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.

> ---
>  arch/x86/include/asm/smap.h   | 33 +++++++++++++++++++++++++++++++--
>  arch/x86/kernel/alternative.c | 28 ++++++++++++++++++++++++++--
>  2 files changed, 57 insertions(+), 4 deletions(-)
>