[PATCH v2 11/11] arm64: Implement branch predictor hardening for affected Cortex-A CPUs

Will Deacon
2018-01-05T13:12:41Z

Cortex-A57, A72, A73 and A75 are susceptible to branch predictor aliasing
and can theoretically be attacked by malicious code.

This patch implements a PSCI-based mitigation for these CPUs when available.
The call into firmware will invalidate the branch predictor state, preventing
any malicious entries from affecting other victim contexts.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/bpi.S | 24 ++++++++++++++++++++++++
arch/arm64/kernel/cpu_errata.c | 42 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 66 insertions(+)

diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S
index 06a931eb2673..2e9146534174 100644
--- a/arch/arm64/kernel/bpi.S
+++ b/arch/arm64/kernel/bpi.S
@@ -53,3 +53,27 @@ ENTRY(__bp_harden_hyp_vecs_start)
vectors __kvm_hyp_vector
.endr
ENTRY(__bp_harden_hyp_vecs_end)
+ENTRY(__psci_hyp_bp_inval_start)
+ sub sp, sp, #(8 * 18)
+ stp x16, x17, [sp, #(16 * 0)]
+ stp x14, x15, [sp, #(16 * 1)]
+ stp x12, x13, [sp, #(16 * 2)]
+ stp x10, x11, [sp, #(16 * 3)]
+ stp x8, x9, [sp, #(16 * 4)]
+ stp x6, x7, [sp, #(16 * 5)]
+ stp x4, x5, [sp, #(16 * 6)]
+ stp x2, x3, [sp, #(16 * 7)]
+ stp x0, x1, [sp, #(18 * 8)]
+ mov x0, #0x84000000
+ smc #0
+ ldp x16, x17, [sp, #(16 * 0)]
+ ldp x14, x15, [sp, #(16 * 1)]
+ ldp x12, x13, [sp, #(16 * 2)]
+ ldp x10, x11, [sp, #(16 * 3)]
+ ldp x8, x9, [sp, #(16 * 4)]
+ ldp x6, x7, [sp, #(16 * 5)]
+ ldp x4, x5, [sp, #(16 * 6)]
+ ldp x2, x3, [sp, #(16 * 7)]
+ ldp x0, x1, [sp, #(18 * 8)]
+ add sp, sp, #(8 * 18)
+ENTRY(__psci_hyp_bp_inval_end)
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 16ea5c6f314e..cb0fb3796bb8 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -53,6 +53,8 @@ static int cpu_enable_trap_ctr_access(void *__unused)
DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);

#ifdef CONFIG_KVM
+extern char __psci_hyp_bp_inval_start[], __psci_hyp_bp_inval_end[];
+
static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
const char *hyp_vecs_end)
{
@@ -94,6 +96,9 @@ static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
spin_unlock(&bp_lock);
}
#else
+#define __psci_hyp_bp_inval_start NULL
+#define __psci_hyp_bp_inval_end NULL
+
static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
const char *hyp_vecs_start,
const char *hyp_vecs_end)
@@ -118,6 +123,21 @@ static void install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry,

__install_bp_hardening_cb(fn, hyp_vecs_start, hyp_vecs_end);
}
+
+#include <linux/psci.h>
+
+static int enable_psci_bp_hardening(void *data)
+{
+ const struct arm64_cpu_capabilities *entry = data;
+
+ if (psci_ops.get_version)
+ install_bp_hardening_cb(entry,
+ (bp_hardening_cb_t)psci_ops.get_version,
+ __psci_hyp_bp_inval_start,
+ __psci_hyp_bp_inval_end);
+
+ return 0;
+}
#endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */

#define MIDR_RANGE(model, min, max) \
@@ -261,6 +281,28 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
},
#endif
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+ {
+ .capability = ARM64_HARDEN_BRANCH_PREDICTOR,
+ MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
+ .enable = enable_psci_bp_hardening,
+ },
+ {
+ .capability = ARM64_HARDEN_BRANCH_PREDICTOR,
+ MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
+ .enable = enable_psci_bp_hardening,
+ },
+ {
+ .capability = ARM64_HARDEN_BRANCH_PREDICTOR,
+ MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
+ .enable = enable_psci_bp_hardening,
+ },
+ {
+ .capability = ARM64_HARDEN_BRANCH_PREDICTOR,
+ MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
+ .enable = enable_psci_bp_hardening,
+ },
+#endif
{
}
};
--
2.1.4