From: George Guo <guodongtai@kylinos.cn>

Date: Tue, 28 Mar 2023 15:13:35 +0800

Subject: [PATCH] LoongArch, bpf: Fix jit to skip speculation barrier opcode

References: bsc#1012628

Patch-mainline: 6.2.12

Git-commit: a6f6a95f25803500079513780d11a911ce551d76

[ Upstream commit a6f6a95f25803500079513780d11a911ce551d76 ]

Just skip the opcode(BPF_ST | BPF_NOSPEC) in the BPF JIT instead of

failing to JIT the entire program, given LoongArch currently has no

couterpart of a speculation barrier instruction. To verify the issue,

use the ltp testcase as shown below.

Also, Wang says:

  I can confirm there's currently no speculation barrier equivalent

  on LonogArch. (Loongson says there are builtin mitigations for

  Spectre-V1 and V2 on their chips, and AFAIK efforts to port the

  exploits to mips/LoongArch have all failed a few years ago.)

Without this patch:

  $ ./bpf_prog02

  [...]

  bpf_common.c:123: TBROK: Failed verification: ??? (524)

  [...]

  Summary:

  passed   0

  failed   0

  broken   1

  skipped  0

  warnings 0

With this patch:

  $ ./bpf_prog02

  [...]

  Summary:

  passed   0

  failed   0

  broken   0

  skipped  0

  warnings 0

Fixes: 5dc615520c4d ("LoongArch: Add BPF JIT support")

Signed-off-by: George Guo <guodongtai@kylinos.cn>

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Acked-by: WANG Xuerui <git@xen0n.name>

Cc: Tiezhu Yang <yangtiezhu@loongson.cn>

Link: https://lore.kernel.org/bpf/20230328071335.2664966-1-guodongtai@kylinos.cn

Signed-off-by: Sasha Levin <sashal@kernel.org>

Signed-off-by: Jiri Slaby <jslaby@suse.cz>

---

 arch/loongarch/net/bpf_jit.c | 4 ++++

 1 file changed, 4 insertions(+)

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c

index 288003a9..d586df48 100644

--- a/arch/loongarch/net/bpf_jit.c

+++ b/arch/loongarch/net/bpf_jit.c

@@ -1022,6 +1022,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext

 		emit_atomic(insn, ctx);

 		break;

+	/* Speculation barrier */

+	case BPF_ST | BPF_NOSPEC:

+		break;

+

 	default:

 		pr_err("bpf_jit: unknown opcode %02x\n", code);

 		return -EINVAL;

-- 

2.35.3