[PATCH v2 3/4] KVM: arm64: Sanitise MTE tags when a permission fault installs a mapping

[Fuad Tabba]

The stage-2 fault path sanitises MTE tags only on translation faults, as
a permission fault normally just relaxes an existing leaf. However, when
the page is backed by a THP, a permission fault at page granule installs
a block whose other pages may never have been mapped or sanitised. Once
dirty logging is off, a guest write to a page mapped read-only during
logging installs the block, and the guest can read the tags those pages'
previous owners left.

Sanitise whenever the fault path calls kvm_pgtable_stage2_map() rather
than relaxing permissions. If the VMM replaces the VMA after the guest
takes a permission fault but before vma_lookup(), that path would map
and sanitise memory from the new VMA without checking it. Run the
VM_MTE_ALLOWED check in kvm_s2_fault_compute_prot() on permission
faults too.

Fixes: ea7fc1bb1cd1b ("KVM: arm64: Introduce MTE VM feature")
Reviewed-by: Lorenzo Stoakes (ARM) <ljs at kernel.org>
Cc: stable at vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
---
 arch/arm64/kvm/mmu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a551b6bb13c21..6e10aa9913d71 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2004,7 +2004,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 	if (s2fd->nested)
 		*prot = adjust_nested_exec_perms(kvm, s2fd->nested, *prot);
 
-	if (!kvm_s2_fault_is_perm(s2fd) && !s2vi->map_non_cacheable && kvm_has_mte(kvm)) {
+	if (!s2vi->map_non_cacheable && kvm_has_mte(kvm)) {
 		/* Check the VMM hasn't introduced a new disallowed VMA */
 		if (!s2vi->mte_allowed)
 			return -EFAULT;
@@ -2059,9 +2059,6 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 		}
 	}
 
-	if (!perm_fault_granule && !s2vi->map_non_cacheable && kvm_has_mte(kvm))
-		sanitise_mte_tags(kvm, pfn, mapping_size);
-
 	/*
 	 * Under the premise of getting a FSC_PERM fault, we just need to relax
 	 * permissions only if mapping_size equals perm_fault_granule. Otherwise,
@@ -2076,6 +2073,9 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, gfn_to_gpa(gfn),
 								 prot, flags);
 	} else {
+		if (!s2vi->map_non_cacheable && kvm_has_mte(kvm))
+			sanitise_mte_tags(kvm, pfn, mapping_size);
+
 		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, gfn_to_gpa(gfn), mapping_size,
 							 __pfn_to_phys(pfn), prot,
 							 memcache, flags);
-- 
2.47.3