arm64: Implement branch predictor hardening for Falkor

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>
[will: fix label name when !CONFIG_KVM and remove references to MIDR_FALKOR]
Signed-off-by: Will Deacon <will.deacon@arm.com>

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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 */

arch/arm64/include/asm/kvm_asm.h

@@ -68,6 +68,8 @@ extern u32 __kvm_get_mdcr_el2(void);
 
 extern u32 __init_stage2_translation(void);
 
+extern void __qcom_hyp_sanitize_btac_predictors(void);
+
 #endif
 
 #endif /* __ARM_KVM_ASM_H__ */

arch/arm64/kernel/bpi.S

@@ -77,3 +77,11 @@ ENTRY(__psci_hyp_bp_inval_start)
 	ldp	x0, x1, [sp, #(16 * 8)]
 	add	sp, sp, #(8 * 18)
 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)

arch/arm64/kernel/cpu_errata.c

@@ -54,6 +54,8 @@ 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[];
+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_end	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 +329,15 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		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_BP_POST_GUEST_EXIT,
+		MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR_V1),
+	},
 #endif
 	{
 	}

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)

arch/arm64/kvm/hyp/switch.c

@@ -406,6 +406,14 @@ 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_V1)
+			__qcom_hyp_sanitize_btac_predictors();
+	}
+
 	fp_enabled = __fpsimd_enabled();
 
 	__sysreg_save_guest_state(guest_ctxt);