On Mon, 7 Jul 2025 11:03:02 +0300
"Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> From: Sohil Mehta <sohil.mehta@xxxxxxxxx>
>
> 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.
...
Or just write a byte copy loop in C with (eg) barrier() inside it
to stop gcc converting it to memcpy().
David
