From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B01121D416C for ; Tue, 5 Aug 2025 11:55:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754394957; cv=none; b=dWGHKUkidMI4cMBRTi9xgeCQL23lEqg48htXYxd71fzlUs/X+4EAOzzaYAYX0Awq7jyCFlZMTFhmhCtP2O9Ik970EQfUMnYXHCElpJPI4L3G+hAx+JlkBvyUbl+QqmrNdnOOBs8KiutwxlHpxHjQHFPM5H8TZYRaXSq3mjw1yE8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754394957; c=relaxed/simple; bh=PggTa6WxH0M5vJFOXlrFPWJ8rRrHvm0EqhGTYumCrl8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=mLtNvh92ifwOCaPI1OrqZrn82KyuZ1o/5IgRalXCvy2ThLsJoH41UZGjHcOfhJ8pgTJ2tXjOEvkEK/eh5Wfcdt2sv/WWS1muTT770/L5Z0uf0lC9jOnIbW4w8XJ5bhAgg1ujaiSGXs/wunbLEf7TBGpgMfFJuOgfvYSG/b6+qIY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ajBeWn2X; arc=none smtp.client-ip=95.215.58.187 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ajBeWn2X" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1754394943; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=1jlTuuY4q/lESnvYBhHYVkc1gTSHmVy1oGeEx4fpCSM=; b=ajBeWn2XwrexaWuIR21f3lKETvQsaivFu7/Bh9NEcLw/K3ibRBIqgnbSx9E0nzxNgiFfQb d0tzCir3CcpXoF5Eyh2o2pOBsvNpj9ZyIQIRuaNu8LjJLKxPeyNJAjxSbKbf2IXOAmENPr 6O/lTfqHD83zpzf3VODLV75nja0rlWs= From: KaFai Wan To: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mrpre@163.com, mannkafai@gmail.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Cc: KaFai Wan , Felix Fietkau Subject: [PATCH bpf-next 1/1] bpf: Allow fall back to interpreter for programs with stack size <= 512 Date: Tue, 5 Aug 2025 19:55:13 +0800 Message-ID: <20250805115513.4018532-1-kafai.wan@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT OpenWRT users reported regression on ARMv6 devices after updating to latest HEAD, where tcpdump filter: tcpdump -i mon1 \ "not wlan addr3 3c37121a2b3c and not wlan addr2 184ecbca2a3a \ and not wlan addr2 14130b4d3f47 and not wlan addr2 f0f61cf440b7 \ and not wlan addr3 a84b4dedf471 and not wlan addr3 d022be17e1d7 \ and not wlan addr3 5c497967208b and not wlan addr2 706655784d5b" fails with warning: "Kernel filter failed: No error information" when using config: # CONFIG_BPF_JIT_ALWAYS_ON is not set CONFIG_BPF_JIT_DEFAULT_ON=y The issue arises because commits: 1. "bpf: Fix array bounds error with may_goto" changed default runtime to __bpf_prog_ret0_warn when jit_requested = 1 2. "bpf: Avoid __bpf_prog_ret0_warn when jit fails" returns error when jit_requested = 1 but jit fails This change restores interpreter fallback capability for BPF programs with stack size <= 512 bytes when jit fails. Reported-by: Felix Fietkau Closes: https://lore.kernel.org/bpf/2e267b4b-0540-45d8-9310-e127bf95fc63@nbd.name/ Fixes: 6ebc5030e0c5 ("bpf: Fix array bounds error with may_goto") Fixes: 86bc9c742426 ("bpf: Avoid __bpf_prog_ret0_warn when jit fails") Signed-off-by: KaFai Wan --- kernel/bpf/core.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 5d1650af899d..2d86bd4b0b97 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2366,8 +2366,8 @@ static unsigned int __bpf_prog_ret0_warn(const void *ctx, const struct bpf_insn *insn) { /* If this handler ever gets executed, then BPF_JIT_ALWAYS_ON - * is not working properly, or interpreter is being used when - * prog->jit_requested is not 0, so warn about it! + * or may_goto may cause stack size > 512 is not working properly, + * so warn about it! */ WARN_ON_ONCE(1); return 0; @@ -2478,10 +2478,10 @@ static void bpf_prog_select_func(struct bpf_prog *fp) * But for non-JITed programs, we don't need bpf_func, so no bounds * check needed. */ - if (!fp->jit_requested && - !WARN_ON_ONCE(idx >= ARRAY_SIZE(interpreters))) { + if (idx < ARRAY_SIZE(interpreters)) { fp->bpf_func = interpreters[idx]; } else { + WARN_ON_ONCE(!fp->jit_requested); fp->bpf_func = __bpf_prog_ret0_warn; } #else @@ -2505,7 +2505,7 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err) /* In case of BPF to BPF calls, verifier did all the prep * work with regards to JITing, etc. */ - bool jit_needed = fp->jit_requested; + bool jit_needed = false; if (fp->bpf_func) goto finalize; @@ -2515,6 +2515,8 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err) jit_needed = true; bpf_prog_select_func(fp); + if (fp->bpf_func == __bpf_prog_ret0_warn) + jit_needed = true; /* eBPF JITs can rewrite the program in case constant * blinding is active. However, in case of error during -- 2.43.0