[PATCH] arm64: Implement branch predictor hardening for Falkor

Shanker Donthineni
2018-01-05T20:28:59Z

Falkor is susceptible to branch predictor aliasing and can
theoretically be attacked by malicious code. This patch
implements a mitigation for these attacks, preventing any
malicious entries from affecting other victim contexts.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
---
This patch has been verified using tip of
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=kpti
and
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm64?h=v4.15-rc6&id=c622cc013cece073722592cff1ac6643a33b1622

arch/arm64/include/asm/cpucaps.h | 3 ++-
arch/arm64/include/asm/kvm_asm.h | 2 ++
arch/arm64/kernel/bpi.S | 8 +++++++
arch/arm64/kernel/cpu_errata.c | 49 ++++++++++++++++++++++++++++++++++++++--
arch/arm64/kvm/hyp/entry.S | 12 ++++++++++
arch/arm64/kvm/hyp/switch.c | 10 ++++++++
6 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 51616e7..7049b48 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -43,7 +43,8 @@
#define ARM64_SVE 22
#define ARM64_UNMAP_KERNEL_AT_EL0 23
#define ARM64_HARDEN_BRANCH_PREDICTOR 24
+#define ARM64_HARDEN_BP_POST_GUEST_EXIT 25

-#define ARM64_NCAPS 25
+#define ARM64_NCAPS 26

#endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index ab4d0a9..24961b7 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -68,6 +68,8 @@

extern u32 __init_stage2_translation(void);

+extern void __qcom_hyp_sanitize_btac_predictors(void);
+
#endif

#endif /* __ARM_KVM_ASM_H__ */
diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S
index 2b10d52..44ffcda 100644
--- a/arch/arm64/kernel/bpi.S
+++ b/arch/arm64/kernel/bpi.S
@@ -77,3 +77,11 @@ ENTRY(__psci_hyp_bp_inval_start)
ldp x2, x3, [sp], #16
ldp x0, x1, [sp], #16
ENTRY(__psci_hyp_bp_inval_end)
+
+ENTRY(__qcom_hyp_sanitize_link_stack_start)
+ stp x29, x30, [sp, #-16]!
+ .rept 16
+ bl . + 4
+ .endr
+ ldp x29, x30, [sp], #16
+ENTRY(__qcom_hyp_sanitize_link_stack_end)
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index cb0fb37..daf53a5 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -54,6 +54,8 @@ static int cpu_enable_trap_ctr_access(void *__unused)

#ifdef CONFIG_KVM
extern char __psci_hyp_bp_inval_start[], __psci_hyp_bp_inval_end[];
+extern char __qcom_hyp_sanitize_link_stack_start[];
+extern char __qcom_hyp_sanitize_link_stack_end[];

static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
const char *hyp_vecs_end)
@@ -96,8 +98,10 @@ 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
+#define __psci_hyp_bp_inval_start NULL
+#define __psci_hyp_bp_inval_end NULL
+#define __qcom_hyp_sanitize_link_stack_start NULL
+#define __qcom_hyp_sanitize_link_stack_start NULL

static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
const char *hyp_vecs_start,
@@ -138,6 +142,29 @@ static int enable_psci_bp_hardening(void *data)

return 0;
}
+
+static void qcom_link_stack_sanitization(void)
+{
+ u64 tmp;
+
+ asm volatile("mov %0, x30 \n"
+ ".rept 16 \n"
+ "bl . + 4 \n"
+ ".endr \n"
+ "mov x30, %0 \n"
+ : "=&r" (tmp));
+}
+
+static int qcom_enable_link_stack_sanitization(void *data)
+{
+ const struct arm64_cpu_capabilities *entry = data;
+
+ install_bp_hardening_cb(entry, qcom_link_stack_sanitization,
+ __qcom_hyp_sanitize_link_stack_start,
+ __qcom_hyp_sanitize_link_stack_end);
+
+ return 0;
+}
#endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */

#define MIDR_RANGE(model, min, max) \
@@ -302,6 +329,24 @@ static int enable_psci_bp_hardening(void *data)
MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
.enable = enable_psci_bp_hardening,
},
+ {
+ .capability = ARM64_HARDEN_BRANCH_PREDICTOR,
+ MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR_V1),
+ .enable = qcom_enable_link_stack_sanitization,
+ },
+ {
+ .capability = ARM64_HARDEN_BRANCH_PREDICTOR,
+ MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR),
+ .enable = qcom_enable_link_stack_sanitization,
+ },
+ {
+ .capability = ARM64_HARDEN_BP_POST_GUEST_EXIT,
+ MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR_V1),
+ },
+ {
+ .capability = ARM64_HARDEN_BP_POST_GUEST_EXIT,
+ MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR),
+ },
#endif
{
}
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 12ee62d..9c45c6a 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -196,3 +196,15 @@ alternative_endif

eret
ENDPROC(__fpsimd_guest_restore)
+
+ENTRY(__qcom_hyp_sanitize_btac_predictors)
+ /**
+ * Call SMC64 with Silicon provider serviceID 23<<8 (0xc2001700)
+ * 0xC2000000-0xC200FFFF: assigned to SiP Service Calls
+ * b15-b0: contains SiP functionID
+ */
+ movz x0, #0x1700
+ movk x0, #0xc200, lsl #16
+ smc #0
+ ret
+ENDPROC(__qcom_hyp_sanitize_btac_predictors)
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 4d273f6..7e37379 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -406,6 +406,16 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
/* 0 falls through to be handled out of EL2 */
}

+ if (cpus_have_const_cap(ARM64_HARDEN_BP_POST_GUEST_EXIT)) {
+ u32 midr = read_cpuid_id();
+
+ /* Apply BTAC predictors mitigation to all Falkor chips */
+ if (((midr & MIDR_CPU_MODEL_MASK) == MIDR_QCOM_FALKOR) ||
+ ((midr & MIDR_CPU_MODEL_MASK) == MIDR_QCOM_FALKOR_V1)) {
+ __qcom_hyp_sanitize_btac_predictors();
+ }
+ }
+
fp_enabled = __fpsimd_enabled();

__sysreg_save_guest_state(guest_ctxt);
--
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Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.