[Qemu-devel] [PATCH 4/5] target-arm: get_phys_addr_lpae: more xn control

[Andrew Jones <drjones@redhat.com>]

This patch makes the following changes to the determination of
whether an address is executable, when translating addresses
using LPAE.

1. No longer assumes that PL0 can't execute when it can't read.
   It can in AArch64, a difference from AArch32.
2. Use va_size == 64 to determine we're in AArch64, rather than
   arm_feature(env, ARM_FEATURE_V8), which is insufficient.
3. Add additional XN determinants
   - NS && is_secure && (SCR & SCR_SIF)
   - WXN && (prot & PAGE_WRITE)
   - AArch64: (prot_PL0 & PAGE_WRITE)
   - AArch32: UWXN && (prot_PL0 & PAGE_WRITE)
   - XN determination should also work in secure mode (untested)
   - XN may even work in EL2 (currently impossible to test)
4. Cleans up the bloated PAGE_EXEC condition - by removing it.

The helper get_S1prot is introduced, which also handles short-
descriptors and v6 XN determination. It may even work in EL2,
when support for that comes, but, as the function name implies,
it only works for stage 1 translations.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 target-arm/helper.c | 111 ++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 86 insertions(+), 25 deletions(-)

diff --git a/target-arm/helper.c b/target-arm/helper.c
index df78f481e92f4..20e5753bd216d 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -4695,8 +4695,8 @@ static inline bool regime_is_user(CPUARMState *env, ARMMMUIdx mmu_idx)
 /* Translate section/page access permissions to page
  * R/W protection flags
  */
-static inline int get_rw_prot(CPUARMState *env, ARMMMUIdx mmu_idx,
-                              bool is_user, int ap, int domain_prot)
+static int get_rw_prot(CPUARMState *env, ARMMMUIdx mmu_idx,
+                       bool is_user, int ap, int domain_prot)
 {
     bool simple_ap = regime_using_lpae_format(env, mmu_idx)
                          || (regime_sctlr(env, mmu_idx) & SCTLR_AFE);
@@ -4762,6 +4762,84 @@ static inline int get_rw_prot(CPUARMState *env, ARMMMUIdx mmu_idx,
     }
 }
 
+/* Translate section/page access permissions to protection flags */
+static int get_S1prot(CPUARMState *env, ARMMMUIdx mmu_idx, bool is_aa64,
+                      int ap, int domain_prot, int ns, int xn, int pxn)
+{
+    bool domain_prot_valid = !regime_using_lpae_format(env, mmu_idx);
+    bool is_user = regime_is_user(env, mmu_idx);
+    bool have_wxn;
+    int prot_rw, user_rw;
+    int wxn = 0;
+
+    assert(mmu_idx != ARMMMUIdx_S2NS);
+
+    if (domain_prot_valid && domain_prot == 3) {
+        return PAGE_READ | PAGE_WRITE | PAGE_EXEC;
+    }
+
+    user_rw = get_rw_prot(env, mmu_idx, true, ap, domain_prot);
+    if (is_user) {
+        prot_rw = user_rw;
+    } else {
+        prot_rw = get_rw_prot(env, mmu_idx, false, ap, domain_prot);
+    }
+
+    if (ns && arm_is_secure(env) && (env->cp15.scr_el3 & SCR_SIF)) {
+        return prot_rw;
+    }
+
+    /* TODO have_wxn should be replaced with arm_feature(env, ARM_FEATURE_EL2),
+     * when ARM_FEATURE_EL2 starts getting set. For now we assume all v7
+     * compatible processors have EL2, which is required for [U]WXN.
+     */
+    have_wxn = arm_feature(env, ARM_FEATURE_V7);
+
+    if (have_wxn) {
+        wxn = regime_sctlr(env, mmu_idx) & SCTLR_WXN;
+    }
+
+    if (is_aa64) {
+        assert(arm_feature(env, ARM_FEATURE_V8));
+        switch (regime_el(env, mmu_idx)) {
+        case 1:
+            if (is_user && !user_rw) {
+                wxn = 0;
+            } else if (!is_user) {
+                xn = pxn || (user_rw & PAGE_WRITE);
+            }
+            break;
+        case 2:
+        case 3:
+            break;
+        }
+    } else if (arm_feature(env, ARM_FEATURE_V6K)) {
+        switch (regime_el(env, mmu_idx)) {
+        case 1:
+        case 3:
+            if (is_user) {
+                xn = xn || !user_rw;
+            } else {
+                int uwxn = 0;
+                if (have_wxn) {
+                    uwxn = regime_sctlr(env, mmu_idx) & SCTLR_UWXN;
+                }
+                xn = xn || !prot_rw || pxn || (uwxn && (user_rw & PAGE_WRITE));
+            }
+            break;
+        case 2:
+            break;
+        }
+    } else {
+        xn = wxn = 0;
+    }
+
+    if (xn || (wxn && (prot_rw & PAGE_WRITE))) {
+        return prot_rw;
+    }
+    return prot_rw | PAGE_EXEC;
+}
+
 static bool get_level1_table_address(CPUARMState *env, ARMMMUIdx mmu_idx,
                                      uint32_t *table, uint32_t address)
 {
@@ -5047,7 +5125,6 @@ static int get_phys_addr_lpae(CPUARMState *env, target_ulong address,
     int32_t granule_sz = 9;
     int32_t va_size = 32;
     int32_t tbi = 0;
-    bool is_user;
     TCR *tcr = regime_tcr(env, mmu_idx);
 
     /* TODO:
@@ -5220,31 +5297,15 @@ static int get_phys_addr_lpae(CPUARMState *env, target_ulong address,
         /* Access flag */
         goto do_fault;
     }
+
+    *prot = get_S1prot(env, mmu_idx, va_size == 64, extract32(attrs, 4, 2), 0,
+                       extract32(attrs, 3, 1), extract32(attrs, 12, 1),
+                       extract32(attrs, 11, 1));
+
     fault_type = permission_fault;
-    is_user = regime_is_user(env, mmu_idx);
-    if (is_user && !(attrs & (1 << 4))) {
-        /* Unprivileged access not enabled */
+    if (!(*prot & (1 << access_type))) {
         goto do_fault;
     }
-    *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
-    if ((arm_feature(env, ARM_FEATURE_V8) && is_user && (attrs & (1 << 12))) ||
-        (!arm_feature(env, ARM_FEATURE_V8) && (attrs & (1 << 12))) ||
-        (!is_user && (attrs & (1 << 11)))) {
-        /* XN/UXN or PXN. Since we only implement EL0/EL1 we unconditionally
-         * treat XN/UXN as UXN for v8.
-         */
-        if (access_type == 2) {
-            goto do_fault;
-        }
-        *prot &= ~PAGE_EXEC;
-    }
-    if (attrs & (1 << 5)) {
-        /* Write access forbidden */
-        if (access_type == 1) {
-            goto do_fault;
-        }
-        *prot &= ~PAGE_WRITE;
-    }
 
     *phys_ptr = descaddr;
     *page_size_ptr = page_size;
-- 
1.9.3