On Fri, Aug 11, 2023 at 04:09:33PM +0100, Catalin Marinas wrote:
On Mon, Aug 07, 2023 at 11:00:22PM +0100, Mark Brown wrote:
if (is_write_abort(esr) &&!(is_gcs_fault(esr) || is_el1_data_abort(esr)))return VM_FAULT_BADACCESS;
Related to my PIE permissions comment: when do we have a valid EL1 data write abort that's not a GCS fault? Does a faulting GCSSTTR set the ESR_ELx_GCS bit?
Yes, it should do. The GCS instructions have access descriptors created with CreateAccDescGCS() which results in the access being flagged as a GCS access.
- } else {
/** GCS faults should never happen for pages that are* not part of a GCS and the operation being attempted* can never succeed.*/if (is_gcs_fault(esr))return VM_FAULT_BADACCESS;
If one does a GCS push/store to a non-GCS page, do we get a GCS fault or something else? I couldn't figure out from the engineering spec. If the hardware doesn't generate such exceptions, we might as well remove this 'else' branch. But maybe it does generate a GCS-specific fault as you added a similar check in is_invalid_el0_gcs_access().
Yes, see AddGCSRecord() and LoadCheckGCSRecord() - all GCS initiated accesses need to be AccDescGCS so appropriate permissions enforcement can happen and that's what causes the fault to be flagged as GCS.
@@ -595,6 +644,19 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, if (!vma) goto lock_mmap;
- /*
* We get legitimate write faults for GCS pages from GCS* operations and from EL1 writes to EL0 pages but just plain
What are the EL1 writes to the shadow stack? Would it not use copy_to_user_gcs()?
They should, yes - I'll reword the comment.