On 10/28/24 21:22, Linus Torvalds wrote:
> On Mon, 28 Oct 2024 at 10:18, Lorenzo Stoakes
> <lorenzo.stoakes@xxxxxxxxxx> 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.
VM_MTE_ALLOWED is also set by arm64's arch_calc_vm_flag_bits():
if (system_supports_mte() && (flags & MAP_ANONYMOUS))
return VM_MTE_ALLOWED;
And there's also this in arch/arm64/include/asm/page.h
#define VM_DATA_DEFAULT_FLAGS (VM_DATA_FLAGS_TSK_EXEC | VM_MTE_ALLOWED)
So it would need to all be considered in the validation if we wanted to
replace VM_MTE_ALLOWED completely?
> 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
