Abort the page walk, if permission checks fail on any page table level, by moving the check to within the page walker loop. Currently, the page walker only checks for access flags after successfully walking the entire paging structure. This change is needed later to enable setting accessed bits in each page table that was successfully visited, during a page walk that ultimately failed. As a result, error codes returned by the page walker may observe a change in behaviour, specifically, the error code will be built as soon as an access violation is found, meaning that for example, if an access violation is detected on page level 4, the page walker will abort the walk without looking at level 3 and below. However, since the error code returned is built from the passed access requirements, regardless of the actual cause of the failure, it will only be different if there is an access violation in one level and a PKRU violation in a lower one. Previously the error code would include this PKRU violation, whereas now it does not, which is still in line with the behaviour specified in Intel's SDM. The exact procedure to test for violations is currently not specified in the SDM, but aborting the page walk early seems to be a reasonable implementation detail. As KVM does not read the PK bit anywhere, this only results in a different page-fault error codes for guests. Signed-off-by: Nikolas Wipper <nikwip@xxxxxxxxx> --- arch/x86/kvm/mmu/paging_tmpl.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index ae7d39ff2d07..d9c3c78b3c14 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -422,6 +422,12 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, goto error; } + /* Convert to ACC_*_MASK flags for struct guest_walker. */ + walker->pte_access = FNAME(gpte_access)(pte_access ^ walk_nx_mask); + errcode = permission_fault(vcpu, mmu, walker->pte_access, pte_pkey, access); + if (unlikely(errcode)) + goto error; + walker->ptes[walker->level - 1] = pte; /* Convert to ACC_*_MASK flags for struct guest_walker. */ @@ -431,12 +437,6 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, pte_pkey = FNAME(gpte_pkeys)(vcpu, pte); accessed_dirty = have_ad ? pte_access & PT_GUEST_ACCESSED_MASK : 0; - /* Convert to ACC_*_MASK flags for struct guest_walker. */ - walker->pte_access = FNAME(gpte_access)(pte_access ^ walk_nx_mask); - errcode = permission_fault(vcpu, mmu, walker->pte_access, pte_pkey, access); - if (unlikely(errcode)) - goto error; - gfn = gpte_to_gfn_lvl(pte, walker->level); gfn += (addr & PT_LVL_OFFSET_MASK(walker->level)) >> PAGE_SHIFT; -- 2.40.1 Amazon Web Services Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597
