On Mon, 28 Oct 2024 at 08:57, Lorenzo Stoakes
<lorenzo.stoakes@xxxxxxxxxx> wrote:
>
> So likely hook on your mapping changes flags to set VM_MTE | VM_MTE_ALLOWED and
> expects this to be checked after (ugh).
Gaah. Yes. mm/shmem.c: shmem_mmap() does
/* arm64 - allow memory tagging on RAM-based files */
vm_flags_set(vma, VM_MTE_ALLOWED);
and while I found the equivalent hack for the VM_SPARC_ADI case, I
hadn't noticed that MTE thing.
How very annoying.
So the arch_validate_flags() case does need to be done after the ->mmap() call.
How about just finalizing everything, and then doing a regular
munmap() afterwards and returning an error (all still holding the mmap
semaphore, of course).
That still avoids the whole "partially completed mmap" case.
Linus
