[PATCH hotfix 6.12 v2 4/8] mm: resolve faulty mmap_region() error path behaviour

[Linus Torvalds]

On Mon, 28 Oct 2024 at 10:18, Lorenzo Stoakes
<lorenzo.stoakes at oracle.com> wrote:
>
> I'm genuinely not opposed to a horrible, awful:
>
> #ifdef CONFIG_ARM64
>         if (file && file->f_ops == shmem_file_operations)
>                 vm_flags |= VM_MTE_ALLOWED;
> #endif
>
> Early in the operation prior to the arch_validate_flags() check.

I would just put it inside the arm64 code itself.

IOW, get rid of the VM_MTE_ALLOWED flag entirely, and just make the
arm64 arch_validate_flags() code do something like

        if (flags & VM_MTE) {
                if (file->f_ops != shmem_file_operations)
                        return false;
        }

and be done with it.

Considering that we only have that horrendous arch_validate_flags()
for two architectures, and that they both just have magical special
cases for MTE-like behavior, I do think that just making it be a hack
inside those functions is the way to go.

              Linus