ARM: spectre-v2: add firmware based hardening

Add firmware based hardening for cores that require more complex
handling in firmware.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Boot-tested-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/mm/proc-v7-bugs.c

 // SPDX-License-Identifier: GPL-2.0
+#include <linux/arm-smccc.h>
 #include <linux/kernel.h>
+#include <linux/psci.h>
 #include <linux/smp.h>
 
 #include <asm/cp15.h>
 #include <asm/cputype.h>
+#include <asm/proc-fns.h>
 #include <asm/system_misc.h>
 
 #ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 DEFINE_PER_CPU(harden_branch_predictor_fn_t, harden_branch_predictor_fn);
 
+extern void cpu_v7_smc_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm);
+extern void cpu_v7_hvc_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm);
+
 static void harden_branch_predictor_bpiall(void)
 {
 	write_sysreg(0, BPIALL);
@@ -19,6 +25,16 @@ static void harden_branch_predictor_iciallu(void)
 	write_sysreg(0, ICIALLU);
 }
 
+static void __maybe_unused call_smc_arch_workaround_1(void)
+{
+	arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
+}
+
+static void __maybe_unused call_hvc_arch_workaround_1(void)
+{
+	arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
+}
+
 static void cpu_v7_spectre_init(void)
 {
 	const char *spectre_v2_method = NULL;
@@ -45,7 +61,51 @@ static void cpu_v7_spectre_init(void)
 			harden_branch_predictor_iciallu;
 		spectre_v2_method = "ICIALLU";
 		break;
+
+#ifdef CONFIG_ARM_PSCI
+	default:
+		/* Other ARM CPUs require no workaround */
+		if (read_cpuid_implementor() == ARM_CPU_IMP_ARM)
+			break;
+		/* fallthrough */
+		/* Cortex A57/A72 require firmware workaround */
+	case ARM_CPU_PART_CORTEX_A57:
+	case ARM_CPU_PART_CORTEX_A72: {
+		struct arm_smccc_res res;
+
+		if (psci_ops.smccc_version == SMCCC_VERSION_1_0)
+			break;
+
+		switch (psci_ops.conduit) {
+		case PSCI_CONDUIT_HVC:
+			arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+					  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
+			if ((int)res.a0 != 0)
+				break;
+			per_cpu(harden_branch_predictor_fn, cpu) =
+				call_hvc_arch_workaround_1;
+			processor.switch_mm = cpu_v7_hvc_switch_mm;
+			spectre_v2_method = "hypervisor";
+			break;
+
+		case PSCI_CONDUIT_SMC:
+			arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+					  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
+			if ((int)res.a0 != 0)
+				break;
+			per_cpu(harden_branch_predictor_fn, cpu) =
+				call_smc_arch_workaround_1;
+			processor.switch_mm = cpu_v7_smc_switch_mm;
+			spectre_v2_method = "firmware";
+			break;
+
+		default:
+			break;
+		}
 	}
+#endif
+	}
+
 	if (spectre_v2_method)
 		pr_info("CPU%u: Spectre v2: using %s workaround\n",
 			smp_processor_id(), spectre_v2_method);

arch/arm/mm/proc-v7.S

@@ -9,6 +9,7 @@
  *
  *  This is the "shell" of the ARMv7 processor support.
  */
+#include <linux/arm-smccc.h>
 #include <linux/init.h>
 #include <linux/linkage.h>
 #include <asm/assembler.h>
@@ -93,6 +94,26 @@ ENTRY(cpu_v7_dcache_clean_area)
 	ret	lr
 ENDPROC(cpu_v7_dcache_clean_area)
 
+#ifdef CONFIG_ARM_PSCI
+	.arch_extension sec
+ENTRY(cpu_v7_smc_switch_mm)
+	stmfd	sp!, {r0 - r3}
+	movw	r0, #:lower16:ARM_SMCCC_ARCH_WORKAROUND_1
+	movt	r0, #:upper16:ARM_SMCCC_ARCH_WORKAROUND_1
+	smc	#0
+	ldmfd	sp!, {r0 - r3}
+	b	cpu_v7_switch_mm
+ENDPROC(cpu_v7_smc_switch_mm)
+	.arch_extension virt
+ENTRY(cpu_v7_hvc_switch_mm)
+	stmfd	sp!, {r0 - r3}
+	movw	r0, #:lower16:ARM_SMCCC_ARCH_WORKAROUND_1
+	movt	r0, #:upper16:ARM_SMCCC_ARCH_WORKAROUND_1
+	hvc	#0
+	ldmfd	sp!, {r0 - r3}
+	b	cpu_v7_switch_mm
+ENDPROC(cpu_v7_smc_switch_mm)
+#endif
 ENTRY(cpu_v7_iciallu_switch_mm)
 	mov	r3, #0
 	mcr	p15, 0, r3, c7, c5, 0		@ ICIALLU