From: george <dongtai.guo@linux.dev>
To: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>,
Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
Tiezhu Yang <yangtiezhu@loongson.cn>,
Hengqi Chen <hengqi.chen@gmail.com>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Youling Tang <tangyouling@loongson.cn>
Cc: bpf@vger.kernel.org, loongarch@lists.linux.dev,
linux-kernel@vger.kernel.org, George Guo <guodongtai@kylinos.cn>,
Bing Huang <huangbing@kylinos.cn>,
george <dongtai.guo@linux.dev>
Subject: [PATCH] LoongArch: BPF: Fix sign extension for 12-bit immediates
Date: Mon, 03 Nov 2025 16:42:19 +0800 [thread overview]
Message-ID: <20251103-1-v1-1-20e6641a57da@linux.dev> (raw)
From: George Guo <guodongtai@kylinos.cn>
When loading immediate values that fit within 12-bit signed range,
the move_imm function incorrectly used zero extension instead of
sign extension.
The bug was exposed when scx_simple scheduler failed with -EINVAL
in ops.init() after passing node = -1 to scx_bpf_create_dsq().
Due to incorrect sign extension, `node >= (int)nr_node_ids`
evaluated to true instead of false, causing BPF program failure.
Verified by testing with the scx_simple scheduler (located in
tools/sched_ext/). After building with `make` and running
./tools/sched_ext/build/bin/scx_simple, the scheduler now
initializes successfully with this fix.
Fix this by using sign extension (sext) instead of zero extension
for signed immediate values in move_imm.
Fixes: 5dc615520c4d ("LoongArch: Add BPF JIT support")
Reported-by: Bing Huang <huangbing@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
Signed-off-by: george <dongtai.guo@linux.dev>
---
arch/loongarch/net/bpf_jit.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/loongarch/net/bpf_jit.h b/arch/loongarch/net/bpf_jit.h
index 5697158fd1645fdc3d83f598b00a9e20dfaa8f6d..f1398eb135b69ae61a27ed81f80b4bb0788cf0a0 100644
--- a/arch/loongarch/net/bpf_jit.h
+++ b/arch/loongarch/net/bpf_jit.h
@@ -122,7 +122,8 @@ static inline void move_imm(struct jit_ctx *ctx, enum loongarch_gpr rd, long imm
/* addiw rd, $zero, imm_11_0 */
if (is_signed_imm12(imm)) {
emit_insn(ctx, addiw, rd, LOONGARCH_GPR_ZERO, imm);
- goto zext;
+ emit_sext_32(ctx, rd, is32);
+ return;
}
/* ori rd, $zero, imm_11_0 */
---
base-commit: 6146a0f1dfae5d37442a9ddcba012add260bceb0
change-id: 20251103-1-96faa240e8f4
Best regards,
--
george <dongtai.guo@linux.dev>
next reply other threads:[~2025-11-03 8:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-03 8:42 george [this message]
2025-11-04 6:53 ` Hengqi Chen
2025-12-19 9:20 ` George Guo
2025-12-19 9:33 ` Xi Ruoyao
2025-12-29 7:06 ` George Guo
2025-12-29 14:20 ` Hengqi Chen
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