KVM: arm64: Allocate hyp vectors statically

The EL2 vectors installed when a guest is running point at one of the
following configurations for a given CPU:

  - Straight at __kvm_hyp_vector
  - A trampoline containing an SMC sequence to mitigate Spectre-v2 and
    then a direct branch to __kvm_hyp_vector
  - A dynamically-allocated trampoline which has an indirect branch to
    __kvm_hyp_vector
  - A dynamically-allocated trampoline containing an SMC sequence to
    mitigate Spectre-v2 and then an indirect branch to __kvm_hyp_vector

The indirect branches mean that VA randomization at EL2 isn't trivially
bypassable using Spectre-v3a (where the vector base is readable by the
guest).

Rather than populate these vectors dynamically, configure everything
statically and use an enumerated type to identify the vector "slot"
corresponding to one of the configurations above. This both simplifies
the code, but also makes it much easier to implement at EL2 later on.

Signed-off-by: Will Deacon <will@kernel.org>
[maz: fixed double call to kvm_init_vector_slots() on nVHE]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20201113113847.21619-8-will@kernel.org

1 files changed, 34 insertions, 2 deletions

diff --git a/arch/arm64/include/asm/spectre.h b/arch/arm64/include/asm/spectre.h
index d22f8b7d9c50..fa86b8f655b7 100644
--- a/arch/arm64/include/asm/spectre.h
+++ b/arch/arm64/include/asm/spectre.h
@@ -28,11 +28,41 @@ enum mitigation_state {
 
 struct task_struct;
 
+/*
+ * Note: the order of this enum corresponds to __bp_harden_hyp_vecs and
+ * we rely on having the direct vectors first.
+ */
+enum arm64_hyp_spectre_vector {
+	/*
+	 * Take exceptions directly to __kvm_hyp_vector. This must be
+	 * 0 so that it used by default when mitigations are not needed.
+	 */
+	HYP_VECTOR_DIRECT,
+
+	/*
+	 * Bounce via a slot in the hypervisor text mapping of
+	 * __bp_harden_hyp_vecs, which contains an SMC call.
+	 */
+	HYP_VECTOR_SPECTRE_DIRECT,
+
+	/*
+	 * Bounce via a slot in a special mapping of __bp_harden_hyp_vecs
+	 * next to the idmap page.
+	 */
+	HYP_VECTOR_INDIRECT,
+
+	/*
+	 * Bounce via a slot in a special mapping of __bp_harden_hyp_vecs
+	 * next to the idmap page, which contains an SMC call.
+	 */
+	HYP_VECTOR_SPECTRE_INDIRECT,
+};
+
 typedef void (*bp_hardening_cb_t)(void);
 
 struct bp_hardening_data {
-	int			hyp_vectors_slot;
-	bp_hardening_cb_t	fn;
+	enum arm64_hyp_spectre_vector	slot;
+	bp_hardening_cb_t		fn;
 };
 
 DECLARE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
@@ -53,6 +83,8 @@ enum mitigation_state arm64_get_spectre_v2_state(void);
 bool has_spectre_v2(const struct arm64_cpu_capabilities *cap, int scope);
 void spectre_v2_enable_mitigation(const struct arm64_cpu_capabilities *__unused);
 
+void cpu_el2_vector_harden_enable(const struct arm64_cpu_capabilities *__unused);
+
 enum mitigation_state arm64_get_spectre_v4_state(void);
 bool has_spectre_v4(const struct arm64_cpu_capabilities *cap, int scope);
 void spectre_v4_enable_mitigation(const struct arm64_cpu_capabilities *__unused);