target/loongarch: Preserve PTE permission bits in LDPTE

The LDPTE helper loads a page table entry (or huge page entry) from guest
memory and currently applies the PALEN mask to the whole 64-bit value.

That mask is intended to constrain the physical address bits, but masking
the full entry also clears upper permission bits in the PTE, including NX
(bit 62). As a result, LoongArch TCG can incorrectly allow instruction
fetches from NX mappings when translation is driven through software
page-walk.

Fix this by masking only the PPN/address field with PALEN while preserving
permission bits, and by clearing any non-architectural (software) bits
using a hardware PTE mask. LDDIR is unchanged since it returns the base
address of the next page table level.

Reported at: https://gitlab.com/qemu-project/qemu/-/issues/3319

-Fixes: 56599a705f2 ("target/loongarch: Introduce loongarch_palen_mask()")
Fixes: f757a2cd6948 ("target/loongarch: Add LoongArch interrupt and exception handler")
Cc: qemu-stable@nongnu.org
Signed-off-by: rail5 (Andrew S. Rightenburg) <andrew@rail5.org>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>
(cherry picked from commit 2d877bc02a3b94998cbdd784d194c173d308a98a)
(Mjt: backport to 10.1.x which lacks v10.2.0-1568-g56599a705f
 "target/loongarch: Introduce loongarch_palen_mask()")
(fixing the Fixes: tag)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

3 files changed, 32 insertions, 3 deletions

diff --git a/target/loongarch/cpu.c b/target/loongarch/cpu.c
index 9ca85a56a2..266b0b97d0 100644
--- a/target/loongarch/cpu.c
+++ b/target/loongarch/cpu.c
@@ -575,6 +575,17 @@ static void loongarch_cpu_reset_hold(Object *obj, ResetType type)
 
 #ifdef CONFIG_TCG
     env->fcsr0_mask = FCSR0_M1 | FCSR0_M2 | FCSR0_M3;
+
+    if (is_la64(env)) {
+        env->hw_pte_mask = MAKE_64BIT_MASK(0, 9) |
+                           R_TLBENTRY_64_PPN_MASK |
+                           R_TLBENTRY_64_NR_MASK |
+                           R_TLBENTRY_64_NX_MASK |
+                           R_TLBENTRY_64_RPLV_MASK;
+    } else {
+        env->hw_pte_mask = MAKE_64BIT_MASK(0, 9) |
+                           R_TLBENTRY_32_PPN_MASK;
+    }
 #endif
     env->fcsr0 = 0x0;
 
diff --git a/target/loongarch/cpu.h b/target/loongarch/cpu.h
index 9538e8d61d..65b702938f 100644
--- a/target/loongarch/cpu.h
+++ b/target/loongarch/cpu.h
@@ -380,6 +380,7 @@ typedef struct CPUArchState {
     uint32_t fcsr0_mask;
     uint64_t lladdr; /* LL virtual address compared against SC */
     uint64_t llval;
+    uint64_t hw_pte_mask; /* Mask of architecturally-defined (hardware) PTE bits. */
 #endif
 #ifndef CONFIG_USER_ONLY
 #ifdef CONFIG_TCG
diff --git a/target/loongarch/tcg/tlb_helper.c b/target/loongarch/tcg/tlb_helper.c
index 8872593ff0..9a86b4bb52 100644
--- a/target/loongarch/tcg/tlb_helper.c
+++ b/target/loongarch/tcg/tlb_helper.c
@@ -559,6 +559,20 @@ bool loongarch_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
     cpu_loop_exit_restore(cs, retaddr);
 }
 
+static inline uint64_t loongarch_sanitize_hw_pte(CPULoongArchState *env,
+                                                 uint64_t pte)
+{
+    uint64_t ppn_mask = is_la64(env) ? R_TLBENTRY_64_PPN_MASK : R_TLBENTRY_32_PPN_MASK;
+
+    /*
+     * Keep only architecturally-defined PTE bits. Guests may use some
+     * otherwise-unused bits for software purposes.
+     */
+    pte &= env->hw_pte_mask;
+
+    return (pte & ~ppn_mask) | ((pte & ppn_mask) & TARGET_PHYS_MASK);
+}
+
 target_ulong helper_lddir(CPULoongArchState *env, target_ulong base,
                           target_ulong level, uint32_t mem_idx)
 {
@@ -599,6 +613,7 @@ void helper_ldpte(CPULoongArchState *env, target_ulong base, target_ulong odd,
 {
     CPUState *cs = env_cpu(env);
     target_ulong phys, tmp0, ptindex, ptoffset0, ptoffset1, badv;
+    uint64_t pte_raw;
     uint64_t ptbase = FIELD_EX64(env->CSR_PWCL, CSR_PWCL, PTBASE);
     uint64_t ptwidth = FIELD_EX64(env->CSR_PWCL, CSR_PWCL, PTWIDTH);
     uint64_t dir_base, dir_width;
@@ -611,7 +626,6 @@ void helper_ldpte(CPULoongArchState *env, target_ulong base, target_ulong odd,
      * and the other is the huge page entry,
      * whose bit 6 should be 1.
      */
-    base = base & TARGET_PHYS_MASK;
     if (FIELD_EX64(base, TLBENTRY, HUGE)) {
         /*
          * Gets the huge page level and Gets huge page size.
@@ -635,7 +649,7 @@ void helper_ldpte(CPULoongArchState *env, target_ulong base, target_ulong odd,
          * when loaded into the tlb,
          * so the tlb page size needs to be divided by 2.
          */
-        tmp0 = base;
+        tmp0 = loongarch_sanitize_hw_pte(env, base);
         if (odd) {
             tmp0 += MAKE_64BIT_MASK(ps, 1);
         }
@@ -647,12 +661,15 @@ void helper_ldpte(CPULoongArchState *env, target_ulong base, target_ulong odd,
     } else {
         badv = env->CSR_TLBRBADV;
 
+        base = base & TARGET_PHYS_MASK;
+
         ptindex = (badv >> ptbase) & ((1 << ptwidth) - 1);
         ptindex = ptindex & ~0x1;   /* clear bit 0 */
         ptoffset0 = ptindex << 3;
         ptoffset1 = (ptindex + 1) << 3;
         phys = base | (odd ? ptoffset1 : ptoffset0);
-        tmp0 = ldq_phys(cs->as, phys) & TARGET_PHYS_MASK;
+        pte_raw = ldq_le_phys(cs->as, phys);
+        tmp0 = loongarch_sanitize_hw_pte(env, pte_raw);
         ps = ptbase;
     }