[Xen-changelog] [xen stable-4.9] xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12

[patchbot@xxxxxxx]

commit 6e13ad777d331cd534928df720dbf542497231ba
Author:     Julien Grall <julien.grall@xxxxxxxxxx>
AuthorDate: Fri Feb 2 14:19:23 2018 +0000
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Wed Feb 7 08:39:20 2018 -0800

    xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12
    
    In order to avoid aliasing attackes agains the branch predictor, let's
    invalidate the BTB on guest exist. This is made complicated by the fact
    that we cannot take a branch invalidating the BTB.
    
    This is based on the fourth version posted by Marc Zyngier on Linux-arm
    mailing list (see [1]).
    
    This is part of XSA-254.
    
    [1] https://www.spinics.net/lists/arm-kernel/msg632062.html
    
    Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
    Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    (cherry picked from commit 05e0690d03dc6177e614e060ae78001d4f2abde2)
---
 xen/arch/arm/arm32/entry.S | 38 ++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/cpuerrata.c   | 19 +++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
index 828e52c..1ebbe4b 100644
--- a/xen/arch/arm/arm32/entry.S
+++ b/xen/arch/arm/arm32/entry.S
@@ -160,6 +160,44 @@ GLOBAL(hyp_traps_vector)
         b trap_irq                      /* 0x18 - IRQ */
         b trap_fiq                      /* 0x1c - FIQ */
 
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+
+        .align 5
+GLOBAL(hyp_traps_vector_bp_inv)
+        /*
+         * We encode the exception entry in the bottom 3 bits of
+         * SP, and we have to guarantee to be 8 bytes aligned.
+         */
+        add sp, sp, #1                  /* Reset            7 */
+        add sp, sp, #1                  /* Undef            6 */
+        add sp, sp, #1                  /* Hypervisor Call  5 */
+        add sp, sp, #1                  /* Prefetch abort   4 */
+        add sp, sp, #1                  /* Data abort       3 */
+        add sp, sp, #1                  /* Hypervisor       2 */
+        add sp, sp, #1                  /* IRQ              1 */
+        nop                             /* FIQ              0 */
+
+        mcr    p15, 0, r0, c7, c5, 6       /* BPIALL */
+        isb
+
+.macro vect_br val, targ
+        eor     sp, sp, #\val
+        tst     sp, #7
+        eorne   sp, sp, #\val
+        beq     \targ
+.endm
+
+        vect_br 0, trap_fiq
+        vect_br 1, trap_irq
+        vect_br 2, trap_guest_sync
+        vect_br 3, trap_data_abort
+        vect_br 4, trap_prefetch_abort
+        vect_br 5, trap_hypervisor_call
+        vect_br 6, trap_undefined_instruction
+        vect_br 7, trap_reset
+
+#endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */
+
 DEFINE_TRAP_ENTRY(reset)
 DEFINE_TRAP_ENTRY(undefined_instruction)
 DEFINE_TRAP_ENTRY(hypervisor_call)
diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
index 12f15e7..784979e 100644
--- a/xen/arch/arm/cpuerrata.c
+++ b/xen/arch/arm/cpuerrata.c
@@ -194,6 +194,13 @@ install_bp_hardening_vecs(const struct 
arm_cpu_capabilities *entry,
     this_cpu(bp_harden_vecs) = hyp_vecs;
 }
 
+static int enable_bp_inv_hardening(void *data)
+{
+    install_bp_hardening_vecs(data, hyp_traps_vector_bp_inv,
+                              "execute BPIALL");
+    return 0;
+}
+
 #endif
 
 #define MIDR_RANGE(model, min, max)     \
@@ -280,6 +287,18 @@ static const struct arm_cpu_capabilities arm_errata[] = {
         .enable = enable_psci_bp_hardening,
     },
 #endif
+#ifdef CONFIG_ARM32_HARDEN_BRANCH_PREDICTOR
+    {
+        .capability = ARM_HARDEN_BRANCH_PREDICTOR,
+        MIDR_ALL_VERSIONS(MIDR_CORTEX_A12),
+        .enable = enable_bp_inv_hardening,
+    },
+    {
+        .capability = ARM_HARDEN_BRANCH_PREDICTOR,
+        MIDR_ALL_VERSIONS(MIDR_CORTEX_A17),
+        .enable = enable_bp_inv_hardening,
+    },
+#endif
     {},
 };
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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