Patch "LoongArch, bpf: Fix jit to skip speculation barrier opcode" has been added to the 6.2-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    LoongArch, bpf: Fix jit to skip speculation barrier opcode

to the 6.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     loongarch-bpf-fix-jit-to-skip-speculation-barrier-op.patch
and it can be found in the queue-6.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f29d0087bdea75f0c707e01df2551668a7d0dfee
Author: George Guo <guodongtai@xxxxxxxxxx>
Date:   Tue Mar 28 15:13:35 2023 +0800

    LoongArch, bpf: Fix jit to skip speculation barrier opcode
    
    [ 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@xxxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Acked-by: WANG Xuerui <git@xxxxxxxxxx>
    Cc: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20230328071335.2664966-1-guodongtai@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 288003a9f0cae..d586df48ecc64 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;