From 46f17e7d4fb5a21917894d7d37e805194229d4d5 Mon Sep 17 00:00:00 2001 From: Ilya Leoshkevich Date: Tue, 7 May 2024 02:02:49 +0200 Subject: [PATCH] s390/bpf: Emit a barrier for BPF_FETCH instructions [ Upstream commit 68378982f0b21de02ac3c6a11e2420badefcb4bc ] BPF_ATOMIC_OP() macro documentation states that "BPF_ADD | BPF_FETCH" should be the same as atomic_fetch_add(), which is currently not the case on s390x: the serialization instruction "bcr 14,0" is missing. This applies to "and", "or" and "xor" variants too. s390x is allowed to reorder stores with subsequent fetches from different addresses, so code relying on BPF_FETCH acting as a barrier, for example: stw [%r0], 1 afadd [%r1], %r2 ldxw %r3, [%r4] may be broken. Fix it by emitting "bcr 14,0". Note that a separate serialization instruction is not needed for BPF_XCHG and BPF_CMPXCHG, because COMPARE AND SWAP performs serialization itself. Fixes: ba3b86b9cef0 ("s390/bpf: Implement new atomic ops") Reported-by: Puranjay Mohan Closes: https://lore.kernel.org/bpf/mb61p34qvq3wf.fsf@kernel.org/ Signed-off-by: Ilya Leoshkevich Reviewed-by: Puranjay Mohan Link: https://lore.kernel.org/r/20240507000557.12048-1-iii@linux.ibm.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- arch/s390/net/bpf_jit_comp.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 8af02176f68b..62ee557d4b49 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -1311,8 +1311,12 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, EMIT6_DISP_LH(0xeb000000, is32 ? (op32) : (op64), \ (insn->imm & BPF_FETCH) ? src_reg : REG_W0, \ src_reg, dst_reg, off); \ - if (is32 && (insn->imm & BPF_FETCH)) \ - EMIT_ZERO(src_reg); \ + if (insn->imm & BPF_FETCH) { \ + /* bcr 14,0 - see atomic_fetch_{add,and,or,xor}() */ \ + _EMIT2(0x07e0); \ + if (is32) \ + EMIT_ZERO(src_reg); \ + } \ } while (0) case BPF_ADD: case BPF_ADD | BPF_FETCH: