From 91cdb5b36234e6af69d6280f1510e4453707a2b8 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 13 Sep 2021 18:35:34 +0300 Subject: bpf: Introduce BPF nospec instruction for mitigating Spectre v4 commit f5e81d1117501546b7be050c5fbafa6efd2c722c upstream. In case of JITs, each of the JIT backends compiles the BPF nospec instruction /either/ to a machine instruction which emits a speculation barrier /or/ to /no/ machine instruction in case the underlying architecture is not affected by Speculative Store Bypass or has different mitigations in place already. This covers both x86 and (implicitly) arm64: In case of x86, we use 'lfence' instruction for mitigation. 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 (hence only comment in arm64 JIT). Other archs can follow as needed. The BPF nospec instruction is specifically targeting Spectre v4 since i) we don't use a serialization barrier for the Spectre v1 case, and ii) mitigation instructions for v1 and v4 might be different on some archs. The BPF nospec is required for a future commit, where the BPF verifier does annotate intermediate BPF programs with speculation barriers. Co-developed-by: Piotr Krysiuk Co-developed-by: Benedict Schlueter Signed-off-by: Daniel Borkmann Signed-off-by: Piotr Krysiuk Signed-off-by: Benedict Schlueter Acked-by: Alexei Starovoitov [OP: adjusted context for 4.19, drop riscv and ppc32 changes] Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- arch/sparc/net/bpf_jit_comp_64.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/sparc') diff --git a/arch/sparc/net/bpf_jit_comp_64.c b/arch/sparc/net/bpf_jit_comp_64.c index ec4da4dc98f1..1bb1e64d4377 100644 --- a/arch/sparc/net/bpf_jit_comp_64.c +++ b/arch/sparc/net/bpf_jit_comp_64.c @@ -1261,6 +1261,9 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx) emit(opcode | RS1(src) | rs2 | RD(dst), ctx); break; } + /* speculation barrier */ + case BPF_ST | BPF_NOSPEC: + break; /* ST: *(size *)(dst + off) = imm */ case BPF_ST | BPF_MEM | BPF_W: case BPF_ST | BPF_MEM | BPF_H: -- cgit v1.2.3