Merge tag 'arm64_cbpf_mitigation_2025_05_08' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 cBPF BHB mitigation from James Morse:
 "This adds the BHB mitigation into the code JITted for cBPF programs as
  these can be loaded by unprivileged users via features like seccomp.

  The existing mechanisms to disable the BHB mitigation will also
  prevent the mitigation being JITted. In addition, cBPF programs loaded
  by processes with the SYS_ADMIN capability are not mitigated as these
  could equally load an eBPF program that does the same thing.

  For good measure, the list of 'k' values for CPU's local mitigations
  is updated from the version on arm's website"

* tag 'arm64_cbpf_mitigation_2025_05_08' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64: proton-pack: Add new CPUs 'k' values for branch mitigation
  arm64: bpf: Only mitigate cBPF programs loaded by unprivileged users
  arm64: bpf: Add BHB mitigation to the epilogue for cBPF programs
  arm64: proton-pack: Expose whether the branchy loop k value
  arm64: proton-pack: Expose whether the platform is mitigated by firmware
  arm64: insn: Add support for encoding DSB

Author: torvalds

arch/arm64/include/asm/cputype.h

@@ -81,6 +81,7 @@
 #define ARM_CPU_PART_CORTEX_A78AE	0xD42
 #define ARM_CPU_PART_CORTEX_X1		0xD44
 #define ARM_CPU_PART_CORTEX_A510	0xD46
+#define ARM_CPU_PART_CORTEX_X1C		0xD4C
 #define ARM_CPU_PART_CORTEX_A520	0xD80
 #define ARM_CPU_PART_CORTEX_A710	0xD47
 #define ARM_CPU_PART_CORTEX_A715	0xD4D
@@ -168,6 +169,7 @@
 #define MIDR_CORTEX_A78AE	MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A78AE)
 #define MIDR_CORTEX_X1	MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_X1)
 #define MIDR_CORTEX_A510 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A510)
+#define MIDR_CORTEX_X1C MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_X1C)
 #define MIDR_CORTEX_A520 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A520)
 #define MIDR_CORTEX_A710 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A710)
 #define MIDR_CORTEX_A715 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A715)

arch/arm64/include/asm/insn.h

@@ -706,6 +706,7 @@ u32 aarch64_insn_gen_cas(enum aarch64_insn_register result,
 }
 #endif
 u32 aarch64_insn_gen_dmb(enum aarch64_insn_mb_type type);
+u32 aarch64_insn_gen_dsb(enum aarch64_insn_mb_type type);
 u32 aarch64_insn_gen_mrs(enum aarch64_insn_register result,
 			 enum aarch64_insn_system_register sysreg);
 

arch/arm64/include/asm/spectre.h

@@ -97,6 +97,9 @@ enum mitigation_state arm64_get_meltdown_state(void);
 
 enum mitigation_state arm64_get_spectre_bhb_state(void);
 bool is_spectre_bhb_affected(const struct arm64_cpu_capabilities *entry, int scope);
+extern bool __nospectre_bhb;
+u8 get_spectre_bhb_loop_value(void);
+bool is_spectre_bhb_fw_mitigated(void);
 void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *__unused);
 bool try_emulate_el1_ssbs(struct pt_regs *regs, u32 instr);
 

arch/arm64/kernel/proton-pack.c

@@ -891,6 +891,7 @@ static u8 spectre_bhb_loop_affected(void)
 		MIDR_ALL_VERSIONS(MIDR_CORTEX_A78AE),
 		MIDR_ALL_VERSIONS(MIDR_CORTEX_A78C),
 		MIDR_ALL_VERSIONS(MIDR_CORTEX_X1),
+		MIDR_ALL_VERSIONS(MIDR_CORTEX_X1C),
 		MIDR_ALL_VERSIONS(MIDR_CORTEX_A710),
 		MIDR_ALL_VERSIONS(MIDR_CORTEX_X2),
 		MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2),
@@ -999,6 +1000,11 @@ bool is_spectre_bhb_affected(const struct arm64_cpu_capabilities *entry,
 	return true;
 }
 
+u8 get_spectre_bhb_loop_value(void)
+{
+	return max_bhb_k;
+}
+
 static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
 {
 	const char *v = arm64_get_bp_hardening_vector(slot);
@@ -1016,7 +1022,7 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
 	isb();
 }
 
-static bool __read_mostly __nospectre_bhb;
+bool __read_mostly __nospectre_bhb;
 static int __init parse_spectre_bhb_param(char *str)
 {
 	__nospectre_bhb = true;
@@ -1094,6 +1100,11 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
 	update_mitigation_state(&spectre_bhb_state, state);
 }
 
+bool is_spectre_bhb_fw_mitigated(void)
+{
+	return test_bit(BHB_FW, &system_bhb_mitigations);
+}
+
 /* Patched to NOP when enabled */
 void noinstr spectre_bhb_patch_loop_mitigation_enable(struct alt_instr *alt,
 						     __le32 *origptr,

arch/arm64/lib/insn.c

@@ -5,6 +5,7 @@
  *
  * Copyright (C) 2014-2016 Zi Shen Lim <[email protected]>
  */
+#include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/bug.h>
 #include <linux/printk.h>
@@ -1500,43 +1501,41 @@ u32 aarch64_insn_gen_extr(enum aarch64_insn_variant variant,
 	return aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RM, insn, Rm);
 }
 
-u32 aarch64_insn_gen_dmb(enum aarch64_insn_mb_type type)
+static u32 __get_barrier_crm_val(enum aarch64_insn_mb_type type)
 {
-	u32 opt;
-	u32 insn;
-
 	switch (type) {
 	case AARCH64_INSN_MB_SY:
-		opt = 0xf;
-		break;
+		return 0xf;
 	case AARCH64_INSN_MB_ST:
-		opt = 0xe;
-		break;
+		return 0xe;
 	case AARCH64_INSN_MB_LD:
-		opt = 0xd;
-		break;
+		return 0xd;
 	case AARCH64_INSN_MB_ISH:
-		opt = 0xb;
-		break;
+		return 0xb;
 	case AARCH64_INSN_MB_ISHST:
-		opt = 0xa;
-		break;
+		return 0xa;
 	case AARCH64_INSN_MB_ISHLD:
-		opt = 0x9;
-		break;
+		return 0x9;
 	case AARCH64_INSN_MB_NSH:
-		opt = 0x7;
-		break;
+		return 0x7;
 	case AARCH64_INSN_MB_NSHST:
-		opt = 0x6;
-		break;
+		return 0x6;
 	case AARCH64_INSN_MB_NSHLD:
-		opt = 0x5;
-		break;
+		return 0x5;
 	default:
-		pr_err("%s: unknown dmb type %d\n", __func__, type);
+		pr_err("%s: unknown barrier type %d\n", __func__, type);
 		return AARCH64_BREAK_FAULT;
 	}
+}
+
+u32 aarch64_insn_gen_dmb(enum aarch64_insn_mb_type type)
+{
+	u32 opt;
+	u32 insn;
+
+	opt = __get_barrier_crm_val(type);
+	if (opt == AARCH64_BREAK_FAULT)
+		return AARCH64_BREAK_FAULT;
 
 	insn = aarch64_insn_get_dmb_value();
 	insn &= ~GENMASK(11, 8);
@@ -1545,6 +1544,21 @@ u32 aarch64_insn_gen_dmb(enum aarch64_insn_mb_type type)
 	return insn;
 }
 
+u32 aarch64_insn_gen_dsb(enum aarch64_insn_mb_type type)
+{
+	u32 opt, insn;
+
+	opt = __get_barrier_crm_val(type);
+	if (opt == AARCH64_BREAK_FAULT)
+		return AARCH64_BREAK_FAULT;
+
+	insn = aarch64_insn_get_dsb_base_value();
+	insn &= ~GENMASK(11, 8);
+	insn |= (opt << 8);
+
+	return insn;
+}
+
 u32 aarch64_insn_gen_mrs(enum aarch64_insn_register result,
 			 enum aarch64_insn_system_register sysreg)
 {

arch/arm64/net/bpf_jit_comp.c

@@ -7,6 +7,7 @@
 
 #define pr_fmt(fmt) "bpf_jit: " fmt
 
+#include <linux/arm-smccc.h>
 #include <linux/bitfield.h>
 #include <linux/bpf.h>
 #include <linux/filter.h>
@@ -17,6 +18,7 @@
 #include <asm/asm-extable.h>
 #include <asm/byteorder.h>
 #include <asm/cacheflush.h>
+#include <asm/cpufeature.h>
 #include <asm/debug-monitors.h>
 #include <asm/insn.h>
 #include <asm/text-patching.h>
@@ -939,7 +941,51 @@ static void build_plt(struct jit_ctx *ctx)
 		plt->target = (u64)&dummy_tramp;
 }
 
-static void build_epilogue(struct jit_ctx *ctx)
+/* Clobbers BPF registers 1-4, aka x0-x3 */
+static void __maybe_unused build_bhb_mitigation(struct jit_ctx *ctx)
+{
+	const u8 r1 = bpf2a64[BPF_REG_1]; /* aka x0 */
+	u8 k = get_spectre_bhb_loop_value();
+
+	if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY) ||
+	    cpu_mitigations_off() || __nospectre_bhb ||
+	    arm64_get_spectre_v2_state() == SPECTRE_VULNERABLE)
+		return;
+
+	if (capable(CAP_SYS_ADMIN))
+		return;
+
+	if (supports_clearbhb(SCOPE_SYSTEM)) {
+		emit(aarch64_insn_gen_hint(AARCH64_INSN_HINT_CLEARBHB), ctx);
+		return;
+	}
+
+	if (k) {
+		emit_a64_mov_i64(r1, k, ctx);
+		emit(A64_B(1), ctx);
+		emit(A64_SUBS_I(true, r1, r1, 1), ctx);
+		emit(A64_B_(A64_COND_NE, -2), ctx);
+		emit(aarch64_insn_gen_dsb(AARCH64_INSN_MB_ISH), ctx);
+		emit(aarch64_insn_get_isb_value(), ctx);
+	}
+
+	if (is_spectre_bhb_fw_mitigated()) {
+		emit(A64_ORR_I(false, r1, AARCH64_INSN_REG_ZR,
+			       ARM_SMCCC_ARCH_WORKAROUND_3), ctx);
+		switch (arm_smccc_1_1_get_conduit()) {
+		case SMCCC_CONDUIT_HVC:
+			emit(aarch64_insn_get_hvc_value(), ctx);
+			break;
+		case SMCCC_CONDUIT_SMC:
+			emit(aarch64_insn_get_smc_value(), ctx);
+			break;
+		default:
+			pr_err_once("Firmware mitigation enabled with unknown conduit\n");
+		}
+	}
+}
+
+static void build_epilogue(struct jit_ctx *ctx, bool was_classic)
 {
 	const u8 r0 = bpf2a64[BPF_REG_0];
 	const u8 ptr = bpf2a64[TCCNT_PTR];
@@ -952,10 +998,13 @@ static void build_epilogue(struct jit_ctx *ctx)
 
 	emit(A64_POP(A64_ZR, ptr, A64_SP), ctx);
 
+	if (was_classic)
+		build_bhb_mitigation(ctx);
+
 	/* Restore FP/LR registers */
 	emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx);
 
-	/* Set return value */
+	/* Move the return value from bpf:r0 (aka x7) to x0 */
 	emit(A64_MOV(1, A64_R(0), r0), ctx);
 
 	/* Authenticate lr */
@@ -1898,7 +1947,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	}
 
 	ctx.epilogue_offset = ctx.idx;
-	build_epilogue(&ctx);
+	build_epilogue(&ctx, was_classic);
 	build_plt(&ctx);
 
 	extable_align = __alignof__(struct exception_table_entry);
@@ -1961,7 +2010,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 		goto out_free_hdr;
 	}
 
-	build_epilogue(&ctx);
+	build_epilogue(&ctx, was_classic);
 	build_plt(&ctx);
 
 	/* Extra pass to validate JITed code. */