bpf: Mitigate Spectre v1 using barriers

arch/arm64/net/bpf_jit.h

@@ -325,4 +325,9 @@
 #define A64_MRS_SP_EL0(Rt) \
 	aarch64_insn_gen_mrs(Rt, AARCH64_INSN_SYSREG_SP_EL0)
 
+/* Barriers */
+#define A64_SB aarch64_insn_get_sb_value()
+#define A64_DSB_NSH (aarch64_insn_get_dsb_base_value() | 0x7 << 8)
+#define A64_ISB aarch64_insn_get_isb_value()
+
 #endif /* _BPF_JIT_H */

arch/arm64/net/bpf_jit_comp.c

@@ -1581,17 +1581,14 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 			return ret;
 		break;
 
-	/* speculation barrier */
+	/* speculation barrier against v1 and v4 */
 	case BPF_ST | BPF_NOSPEC:
-		/*
-		 * Nothing required here.
-		 *
-		 * In case of arm64, we rely on the firmware mitigation of
-		 * Speculative Store Bypass as controlled via the ssbd kernel
-		 * parameter. Whenever the mitigation is enabled, it works
-		 * for all of the kernel code with no need to provide any
-		 * additional instructions.
-		 */
+		if (alternative_has_cap_likely(ARM64_HAS_SB)) {
+			emit(A64_SB, ctx);
+		} else {
+			emit(A64_DSB_NSH, ctx);
+			emit(A64_ISB, ctx);
+		}
 		break;
 
 	/* ST: *(size *)(dst + off) = imm */
@@ -2762,6 +2759,17 @@ bool bpf_jit_supports_percpu_insn(void)
 	return true;
 }
 
+bool bpf_jit_bypass_spec_v4(void)
+{
+	/* In case of arm64, we rely on the firmware mitigation of Speculative
+	 * Store Bypass as controlled via the ssbd kernel parameter. Whenever
+	 * the mitigation is enabled, it works for all of the kernel code with
+	 * no need to provide any additional instructions. Therefore, skip
+	 * inserting nospec insns against Spectre v4.
+	 */
+	return true;
+}
+
 bool bpf_jit_inlines_helper_call(s32 imm)
 {
 	switch (imm) {

arch/powerpc/net/bpf_jit_comp64.c

@@ -363,6 +363,23 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	return 0;
 }
 
+bool bpf_jit_bypass_spec_v1(void)
+{
+#if defined(CONFIG_PPC_E500) || defined(CONFIG_PPC_BOOK3S_64)
+	return !(security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
+		 security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR));
+#else
+	return true;
+#endif
+}
+
+bool bpf_jit_bypass_spec_v4(void)
+{
+	return !(security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
+		 security_ftr_enabled(SEC_FTR_STF_BARRIER) &&
+		 stf_barrier_type_get() != STF_BARRIER_NONE);
+}
+
 /*
  * We spill into the redzone always, even if the bpf program has its own stackframe.
  * Offsets hardcoded based on BPF_PPC_STACK_SAVE -- see bpf_jit_stack_local()
@@ -390,6 +407,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		       u32 *addrs, int pass, bool extra_pass)
 {
 	enum stf_barrier_type stf_barrier = stf_barrier_type_get();
+	bool sync_emitted, ori31_emitted;
 	const struct bpf_insn *insn = fp->insnsi;
 	int flen = fp->len;
 	int i, ret;
@@ -783,30 +801,52 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 
 		/*
 		 * BPF_ST NOSPEC (speculation barrier)
+		 *
+		 * The following must act as a barrier against both Spectre v1
+		 * and v4 if we requested both mitigations. Therefore, also emit
+		 * 'isync; sync' on E500 or 'ori31' on BOOK3S_64 in addition to
+		 * the insns needed for a Spectre v4 barrier.
+		 *
+		 * If we requested only !bypass_spec_v1 OR only !bypass_spec_v4,
+		 * we can skip the respective other barrier type as an
+		 * optimization.
 		 */
 		case BPF_ST | BPF_NOSPEC:
-			if (!security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) ||
-					!security_ftr_enabled(SEC_FTR_STF_BARRIER))
-				break;
-
-			switch (stf_barrier) {
-			case STF_BARRIER_EIEIO:
-				EMIT(PPC_RAW_EIEIO() | 0x02000000);
-				break;
-			case STF_BARRIER_SYNC_ORI:
+			sync_emitted = false;
+			ori31_emitted = false;
+#ifdef CONFIG_PPC_E500
+			if (!bpf_jit_bypass_spec_v1()) {
+				EMIT(PPC_RAW_ISYNC());
 				EMIT(PPC_RAW_SYNC());
-				EMIT(PPC_RAW_LD(tmp1_reg, _R13, 0));
-				EMIT(PPC_RAW_ORI(_R31, _R31, 0));
-				break;
-			case STF_BARRIER_FALLBACK:
-				ctx->seen |= SEEN_FUNC;
-				PPC_LI64(_R12, dereference_kernel_function_descriptor(bpf_stf_barrier));
-				EMIT(PPC_RAW_MTCTR(_R12));
-				EMIT(PPC_RAW_BCTRL());
-				break;
-			case STF_BARRIER_NONE:
-				break;
+				sync_emitted = true;
+			}
+#endif
+			if (!bpf_jit_bypass_spec_v4()) {
+				switch (stf_barrier) {
+				case STF_BARRIER_EIEIO:
+					EMIT(PPC_RAW_EIEIO() | 0x02000000);
+					break;
+				case STF_BARRIER_SYNC_ORI:
+					if (!sync_emitted)
+						EMIT(PPC_RAW_SYNC());
+					EMIT(PPC_RAW_LD(tmp1_reg, _R13, 0));
+					EMIT(PPC_RAW_ORI(_R31, _R31, 0));
+					ori31_emitted = true;
+					break;
+				case STF_BARRIER_FALLBACK:
+					ctx->seen |= SEEN_FUNC;
+					PPC_LI64(_R12, dereference_kernel_function_descriptor(bpf_stf_barrier));
+					EMIT(PPC_RAW_MTCTR(_R12));
+					EMIT(PPC_RAW_BCTRL());
+					break;
+				case STF_BARRIER_NONE:
+					break;
+				}
 			}
+#ifdef CONFIG_PPC_BOOK3S_64
+			if (!bpf_jit_bypass_spec_v1() && !ori31_emitted)
+				EMIT(PPC_RAW_ORI(_R31, _R31, 0));
+#endif
 			break;
 
 		/*

include/linux/bpf.h

@@ -2268,6 +2268,9 @@ bpf_prog_run_array_uprobe(const struct bpf_prog_array *array,
 	return ret;
 }
 
+bool bpf_jit_bypass_spec_v1(void);
+bool bpf_jit_bypass_spec_v4(void);
+
 #ifdef CONFIG_BPF_SYSCALL
 DECLARE_PER_CPU(int, bpf_prog_active);
 extern struct mutex bpf_stats_enabled_mutex;
@@ -2455,12 +2458,16 @@ static inline bool bpf_allow_uninit_stack(const struct bpf_token *token)
 
 static inline bool bpf_bypass_spec_v1(const struct bpf_token *token)
 {
-	return cpu_mitigations_off() || bpf_token_capable(token, CAP_PERFMON);
+	return bpf_jit_bypass_spec_v1() ||
+		cpu_mitigations_off() ||
+		bpf_token_capable(token, CAP_PERFMON);
 }
 
 static inline bool bpf_bypass_spec_v4(const struct bpf_token *token)
 {
-	return cpu_mitigations_off() || bpf_token_capable(token, CAP_PERFMON);
+	return bpf_jit_bypass_spec_v4() ||
+		cpu_mitigations_off() ||
+		bpf_token_capable(token, CAP_PERFMON);
 }
 
 int bpf_map_new_fd(struct bpf_map *map, int flags);

include/linux/bpf_verifier.h

@@ -576,7 +576,8 @@ struct bpf_insn_aux_data {
 	u64 map_key_state; /* constant (32 bit) key tracking for maps */
 	int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
 	u32 seen; /* this insn was processed by the verifier at env->pass_cnt */
-	bool sanitize_stack_spill; /* subject to Spectre v4 sanitation */
+	bool nospec; /* do not execute this instruction speculatively */
+	bool nospec_result; /* result is unsafe under speculation, nospec must follow */
 	bool zext_dst; /* this insn zero extends dst reg */
 	bool needs_zext; /* alu op needs to clear upper bits */
 	bool storage_get_func_atomic; /* bpf_*_storage_get() with atomic memory alloc */

include/linux/filter.h

@@ -82,7 +82,7 @@ struct ctl_table_header;
 #define BPF_CALL_ARGS	0xe0
 
 /* unused opcode to mark speculation barrier for mitigating
- * Speculative Store Bypass
+ * Spectre v1 and v4
  */
 #define BPF_NOSPEC	0xc0
 

kernel/bpf/core.c

@@ -2102,14 +2102,15 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 #undef COND_JMP
 	/* ST, STX and LDX*/
 	ST_NOSPEC:
-		/* Speculation barrier for mitigating Speculative Store Bypass.
-		 * In case of arm64, we rely on the firmware mitigation as
-		 * controlled via the ssbd kernel parameter. Whenever the
-		 * mitigation is enabled, it works for all of the kernel code
-		 * with no need to provide any additional instructions here.
-		 * In case of x86, we use 'lfence' insn for mitigation. We
-		 * reuse preexisting logic from Spectre v1 mitigation that
-		 * happens to produce the required code on x86 for v4 as well.
+		/* Speculation barrier for mitigating Speculative Store Bypass,
+		 * Bounds-Check Bypass and Type Confusion. In case of arm64, we
+		 * rely on the firmware mitigation as controlled via the ssbd
+		 * kernel parameter. Whenever the mitigation is enabled, it
+		 * works for all of the kernel code with no need to provide any
+		 * additional instructions here. In case of x86, we use 'lfence'
+		 * insn for mitigation. We reuse preexisting logic from Spectre
+		 * v1 mitigation that happens to produce the required code on
+		 * x86 for v4 as well.
 		 */
 		barrier_nospec();
 		CONT;
@@ -3034,6 +3035,21 @@ bool __weak bpf_jit_needs_zext(void)
 	return false;
 }
 
+/* By default, enable the verifier's mitigations against Spectre v1 and v4 for
+ * all archs. The value returned must not change at runtime as there is
+ * currently no support for reloading programs that were loaded without
+ * mitigations.
+ */
+bool __weak bpf_jit_bypass_spec_v1(void)
+{
+	return false;
+}
+
+bool __weak bpf_jit_bypass_spec_v4(void)
+{
+	return false;
+}
+
 /* Return true if the JIT inlines the call to the helper corresponding to
  * the imm.
  *