Re: [RFC PATCH RESEND v2 1/2] mm/memfd: Add support for F_SEAL_FUTURE_EXEC to memfd

[Jeff Xu <jeffxu@chromium.org>]

On Wed, Jan 8, 2025 at 5:57 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Tue, Jan 7, 2025 at 6:21 AM Jeff Xu <jeffxu@chromium.org> wrote:
> > Do you know which code checks for VM_MAYEXEC flag in the mprotect code
> > path ?  it isn't obvious to me, i.e. when I grep the VM_MAYEXEC inside
> > mm path, it only shows one place in mprotect and that doesn't do the
> > work.
> >
> > ~/mm/mm$ grep VM_MAYEXEC *
> > mmap.c: mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
> > mmap.c: vm_flags &= ~VM_MAYEXEC;
> > mprotect.c: if (rier && (vma->vm_flags & VM_MAYEXEC))
> > nommu.c: vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
> > nommu.c: vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
>
> The check happens here:
>
> /* newflags >> 4 shift VM_MAY% in place of VM_% */
> if ((newflags & ~(newflags >> 4)) & VM_ACCESS_FLAGS) {
>     error = -EACCES;
>     break;
> }

Thanks for helping !
-Jeff

>
> Alice