Re: [PATCH] x86/mm: fix lookup_address() to handle physical memory holes in direct mapping

[Jürgen Groß]

On 01.07.24 19:57, Kalra, Ashish wrote:
> On 6/29/2024 5:20 AM, Jürgen Groß wrote:
> > On 28.06.24 22:52, Ashish Kalra wrote:
> > > From: Ashish Kalra <ashish.kalra@xxxxxxx>
> > >
> > > lookup_address_in_pgd_attr() at pte level it is simply returning
> > > pte_offset_kernel() and there does not seem to be a check for
> > > returning NULL if pte_none().
> > >
> > > Fix lookup_address_in_pgd_attr() to add check for pte_none()
> > > after pte_offset_kernel() and return NULL if it is true.
> >
> > Please have a look at the comment above lookup_address(). You should not
> > break the documented behavior without verifying that no caller is relying
> > on the current behavior. If this is fine, please update the comment.
> I don't get that, in this case the PTE does not exist, so as per the comments here lookup_address() should have returned NULL.

There is a PTE, but it is all 0.

There is no _valid_ PTE. No PTE would mean that the related PMD entry (or any
other higher level entry) is invalid.

Remember that the W^X checking needs to be performed _before_ a new PTE is
written.


Juergen