[PATCH] target/arm: Correctly propagate stage 1 BTI guarded bit in a two-stage walk

[PATCH] target/arm: Correctly propagate stage 1 BTI guarded bit in a two-stage walk

[Peter Maydell]

In a two-stage translation, the result of the BTI guarded bit should
be the guarded bit from the first stage of translation, as there is
no BTI guard information in stage two.  Our code tried to do this,
but got it wrong, because we currently have two fields where the GP
bit information might live (ARMCacheAttrs::guarded and
CPUTLBEntryFull::extra::arm::guarded), and we were storing the GP bit
in the latter during the stage 1 walk but trying to copy the former
in combine_cacheattrs().

Remove the duplicated storage, and always use the field in
CPUTLBEntryFull; correctly propagate the stage 1 value to the output
in get_phys_addr_twostage().

Note for stable backports: in v8.0 and earlier the field is named
result->f.guarded, not result->f.extra.arm.guarded.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1950
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/internals.h | 1 -
 target/arm/ptw.c       | 7 +++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/target/arm/internals.h b/target/arm/internals.h
index f7224e6f4d9..c837506e448 100644
--- a/target/arm/internals.h
+++ b/target/arm/internals.h
@@ -1181,7 +1181,6 @@ typedef struct ARMCacheAttrs {
     unsigned int attrs:8;
     unsigned int shareability:2; /* as in the SH field of the VMSAv8-64 PTEs */
     bool is_s2_format:1;
-    bool guarded:1;              /* guarded bit of the v8-64 PTE */
 } ARMCacheAttrs;
 
 /* Fields that are valid upon success. */
diff --git a/target/arm/ptw.c b/target/arm/ptw.c
index 53713e03006..1762b058aec 100644
--- a/target/arm/ptw.c
+++ b/target/arm/ptw.c
@@ -3032,7 +3032,6 @@ static ARMCacheAttrs combine_cacheattrs(uint64_t hcr,
 
     assert(!s1.is_s2_format);
     ret.is_s2_format = false;
-    ret.guarded = s1.guarded;
 
     if (s1.attrs == 0xf0) {
         tagged = true;
@@ -3175,7 +3174,7 @@ static bool get_phys_addr_twostage(CPUARMState *env, S1Translate *ptw,
     hwaddr ipa;
     int s1_prot, s1_lgpgsz;
     ARMSecuritySpace in_space = ptw->in_space;
-    bool ret, ipa_secure;
+    bool ret, ipa_secure, s1_guarded;
     ARMCacheAttrs cacheattrs1;
     ARMSecuritySpace ipa_space;
     uint64_t hcr;
@@ -3202,6 +3201,7 @@ static bool get_phys_addr_twostage(CPUARMState *env, S1Translate *ptw,
      */
     s1_prot = result->f.prot;
     s1_lgpgsz = result->f.lg_page_size;
+    s1_guarded = result->f.extra.arm.guarded;
     cacheattrs1 = result->cacheattrs;
     memset(result, 0, sizeof(*result));
 
@@ -3252,6 +3252,9 @@ static bool get_phys_addr_twostage(CPUARMState *env, S1Translate *ptw,
     result->cacheattrs = combine_cacheattrs(hcr, cacheattrs1,
                                             result->cacheattrs);
 
+    /* No BTI GP information in stage 2, we just use the S1 value */
+    result->f.extra.arm.guarded = s1_guarded;
+
     /*
      * Check if IPA translates to secure or non-secure PA space.
      * Note that VSTCR overrides VTCR and {N}SW overrides {N}SA.
-- 
2.34.1

Re: [PATCH] target/arm: Correctly propagate stage 1 BTI guarded bit in a two-stage walk

[Richard Henderson]

On 10/31/23 10:37, Peter Maydell wrote:
> In a two-stage translation, the result of the BTI guarded bit should
> be the guarded bit from the first stage of translation, as there is
> no BTI guard information in stage two.  Our code tried to do this,
> but got it wrong, because we currently have two fields where the GP
> bit information might live (ARMCacheAttrs::guarded and
> CPUTLBEntryFull::extra::arm::guarded), and we were storing the GP bit
> in the latter during the stage 1 walk but trying to copy the former
> in combine_cacheattrs().
> 
> Remove the duplicated storage, and always use the field in
> CPUTLBEntryFull; correctly propagate the stage 1 value to the output
> in get_phys_addr_twostage().
> 
> Note for stable backports: in v8.0 and earlier the field is named
> result->f.guarded, not result->f.extra.arm.guarded.
> 
> Cc: qemu-stable@nongnu.org
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1950
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   target/arm/internals.h | 1 -
>   target/arm/ptw.c       | 7 +++++--
>   2 files changed, 5 insertions(+), 3 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~