[PATCH] arm64: Fix page permissions for platforms running at EL2

[Ilias Apalodimas]

We currently set both and print both PXN and UXN bits when removing
execution for pages. This happens even in the existing per platform
definitions of 'struct mm_region'.

That's not entirely correct though. For stage-1 translations, if a
platform runs on a translation regime with a single privilege level or the
the translation regime supports two privilege levels and we are not
in EL1&0 with HCR_EL2.{NV, NV1} = {1, 1} only BIT54 (XN) is needed
and BIT53(PXN) is reserved 0.

Currently we support Non-Secure EL2, Non-secure EL2&0 and Non-secure
EL1&0.

We already have get_effective_el() which returns 1 if we are
- Running in EL1 so we assume an EL1 translation regime but without
  checking HCR_EL2.{NV, NV1} != {1,1}
- Running in EL2 with HCR_EL2.E2H = 1

The only problem with the above is that if we are in EL1&0 and
HCR_EL2.{NV1, NV} == {1, 1}, then
- Bit[54] holds the PXN instead of the UXN
- The Effective value of UXN is 0
- Bit[53] is RES0

So let's re-use that function and set PXN only when we are in
and EL[2|1]&0 translation regime.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 arch/arm/cpu/armv8/cache_v8.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
index 12ae9bd06039..1c1e33bec24f 100644
--- a/arch/arm/cpu/armv8/cache_v8.c
+++ b/arch/arm/cpu/armv8/cache_v8.c
@@ -575,8 +575,12 @@ static void pretty_print_block_attrs(u64 pte)

 	if (perm_attrs & PTE_BLOCK_PXN)
 		cnt += snprintf(mem_attrs + cnt, sizeof(mem_attrs) - cnt, "PXN ");
-	if (perm_attrs & PTE_BLOCK_UXN)
-		cnt += snprintf(mem_attrs + cnt, sizeof(mem_attrs) - cnt, "UXN ");
+	if (perm_attrs & PTE_BLOCK_UXN) {
+		if (get_effective_el() == 1)
+			cnt += snprintf(mem_attrs + cnt, sizeof(mem_attrs) - cnt, "UXN ");
+		else
+			cnt += snprintf(mem_attrs + cnt, sizeof(mem_attrs) - cnt, "XN ");
+	}
 	if (perm_attrs & PTE_BLOCK_RO)
 		cnt += snprintf(mem_attrs + cnt, sizeof(mem_attrs) - cnt, "RO");
 	if (!mem_attrs[0])
@@ -1039,13 +1043,29 @@ int pgprot_set_attrs(phys_addr_t addr, size_t size, enum pgprot_attrs perm)

 	switch (perm) {
 	case MMU_ATTR_RO:
-		attrs |= PTE_BLOCK_PXN | PTE_BLOCK_UXN | PTE_BLOCK_RO;
+		/*
+		 * get_effective_el() will return 1 if
+		 * - Running in EL1 so we assume an EL1 translation regime
+		 *   with HCR_EL2.{NV, NV1} != {1,1}
+		 * - Running in EL2 with HCR_EL2.E2H = 1 so we assume an
+		 *   EL2&0 translation regime. Since we don't have accesses
+		 *   from EL0 we don't have to check HCR_EL2.TGE
+		 *
+		 * Both of these requires PXN to be set
+		 */
+		if (get_effective_el() == 1)
+			attrs |= PTE_BLOCK_PXN | PTE_BLOCK_UXN | PTE_BLOCK_RO;
+		else
+			attrs |= PTE_BLOCK_UXN | PTE_BLOCK_RO;
 		break;
 	case MMU_ATTR_RX:
 		attrs |= PTE_BLOCK_RO;
 		break;
 	case MMU_ATTR_RW:
-		attrs |= PTE_BLOCK_PXN | PTE_BLOCK_UXN;
+		if (get_effective_el() == 1)
+			attrs |= PTE_BLOCK_PXN | PTE_BLOCK_UXN;
+		else
+			attrs |= PTE_BLOCK_UXN;
 		break;
 	default:
 		log_err("Unknown attribute %d\n", perm);
--
2.47.2