Re: [PATCH v11 19/39] arm64/mm: Handle GCS data aborts

Mark Brown
2024-08-22T16:44:24Z

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On Thu, Aug 22, 2024 at 05:12:30PM +0100, Catalin Marinas wrote:
> On Thu, Aug 22, 2024 at 02:15:22AM +0100, Mark Brown wrote:

> > +static bool is_invalid_gcs_access(struct vm_area_struct *vma, u64 esr)

> > + } else if (unlikely(vma->vm_flags & VM_SHADOW_STACK)) {
> > + /* Only GCS operations can write to a GCS page */
> > + return is_write_abort(esr);
> > + }

> I don't think that's right. The ESR on this path may not even indicate a
> data abort and ESR.WnR bit check wouldn't make sense.

> I presume we want to avoid an infinite loop on a (writeable) GCS page
> when the user does a normal STR but the CPU raises a permission fault. I
> think this function needs to just return false if !esr_is_data_abort().

Yes, that should check for a data abort. I think I'd formed the
impression that is_write_abort() included that check somehow. As you
say it's to avoid spinning trying to resolve a permission fault for a
write (non-GCS reads to a GCS page are valid), I do think we need the
is_write_abort() since non-GCS reads are valid so something like:

if (!esr_is_data_abort(esr))
return false;

return is_write_abort(esr);

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