[Xen-devel] [PATCH v4 11/19] xen/arm64: Add ARM_SMCCC_ARCH_WORKAROUND_1 BP hardening support

[Julien Grall <julien.grall@xxxxxxx>]

Add the detection and runtime code for ARM_SMCCC_ARCH_WORKAROUND_1.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

---
    Changes in v4:
        - Re-order saving/restoring registers in
          __smccc_workaround_1_smc_start

    Changes in v3:
        - Add the missing call to smc #0.

    Changes in v2:
        - Patch added
---
 xen/arch/arm/arm64/bpi.S    | 13 +++++++++++++
 xen/arch/arm/cpuerrata.c    | 32 +++++++++++++++++++++++++++++++-
 xen/include/asm-arm/smccc.h |  1 +
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/bpi.S b/xen/arch/arm/arm64/bpi.S
index 4b7f1dc21f..981fb83a88 100644
--- a/xen/arch/arm/arm64/bpi.S
+++ b/xen/arch/arm/arm64/bpi.S
@@ -16,6 +16,8 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <asm/smccc.h>
+
 .macro ventry target
     .rept 31
     nop
@@ -81,6 +83,17 @@ ENTRY(__psci_hyp_bp_inval_start)
     add     sp, sp, #(8 * 18)
 ENTRY(__psci_hyp_bp_inval_end)
 
+ENTRY(__smccc_workaround_1_smc_start)
+    sub     sp, sp, #(8 * 4)
+    stp     x2, x3, [sp, #(8 * 0)]
+    stp     x0, x1, [sp, #(8 * 2)]
+    mov     w0, #ARM_SMCCC_ARCH_WORKAROUND_1_FID
+    smc     #0
+    ldp     x2, x3, [sp, #(8 * 0)]
+    ldp     x0, x1, [sp, #(8 * 2)]
+    add     sp, sp, #(8 * 4)
+ENTRY(__smccc_workaround_1_smc_end)
+
 /*
  * Local variables:
  * mode: ASM
diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
index 8d5f8d372a..dec9074422 100644
--- a/xen/arch/arm/cpuerrata.c
+++ b/xen/arch/arm/cpuerrata.c
@@ -147,6 +147,34 @@ install_bp_hardening_vec(const struct arm_cpu_capabilities 
*entry,
     return ret;
 }
 
+extern char __smccc_workaround_1_smc_start[], __smccc_workaround_1_smc_end[];
+
+static bool
+check_smccc_arch_workaround_1(const struct arm_cpu_capabilities *entry)
+{
+    struct arm_smccc_res res;
+
+    /*
+     * Enable callbacks are called on every CPU based on the
+     * capabilities. So double-check whether the CPU matches the
+     * entry.
+     */
+    if ( !entry->matches(entry) )
+        return false;
+
+    if ( smccc_ver < SMCCC_VERSION(1, 1) )
+        return false;
+
+    arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FID,
+                      ARM_SMCCC_ARCH_WORKAROUND_1_FID, &res);
+    if ( res.a0 != ARM_SMCCC_SUCCESS )
+        return false;
+
+    return install_bp_hardening_vec(entry,__smccc_workaround_1_smc_start,
+                                    __smccc_workaround_1_smc_end,
+                                    "call ARM_SMCCC_ARCH_WORKAROUND_1");
+}
+
 extern char __psci_hyp_bp_inval_start[], __psci_hyp_bp_inval_end[];
 
 static int enable_psci_bp_hardening(void *data)
@@ -154,12 +182,14 @@ static int enable_psci_bp_hardening(void *data)
     bool ret = true;
     static bool warned = false;
 
+    if ( check_smccc_arch_workaround_1(data) )
+        return 0;
     /*
      * The mitigation is using PSCI version function to invalidate the
      * branch predictor. This function is only available with PSCI 0.2
      * and later.
      */
-    if ( psci_ver >= PSCI_VERSION(0, 2) )
+    else if ( psci_ver >= PSCI_VERSION(0, 2) )
         ret = install_bp_hardening_vec(data, __psci_hyp_bp_inval_start,
                                        __psci_hyp_bp_inval_end,
                                        "call PSCI get version");
diff --git a/xen/include/asm-arm/smccc.h b/xen/include/asm-arm/smccc.h
index 154772b728..8342cc33fe 100644
--- a/xen/include/asm-arm/smccc.h
+++ b/xen/include/asm-arm/smccc.h
@@ -261,6 +261,7 @@ struct arm_smccc_res {
 /* SMCCC error codes */
 #define ARM_SMCCC_ERR_UNKNOWN_FUNCTION  (-1)
 #define ARM_SMCCC_NOT_SUPPORTED         (-1)
+#define ARM_SMCCC_SUCCESS               (0)
 
 /* SMCCC function identifier range which is reserved for existing APIs */
 #define ARM_SMCCC_RESERVED_RANGE_START  0x0
-- 
2.11.0


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