From nobody Sat Oct 4 20:59:07 2025 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (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 EF62B264A8E for ; Wed, 13 Aug 2025 15:30:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755099040; cv=none; b=BAvxcmacrgHC4rDdHOsxLi9OQN/JzUhhffrW5LeNf5SfRw5mPpQDfZVfDW1ruis7LbTzYpZAwWVJWk/Lu+qJIUQnebOn2Y1m8JjF+Ddu8Hn4GVAom3vp8FUVGODO5UPLlL2xONMk0b6w41hVPNSaHBCS+jQIqUOyR2FCkTZ5GZI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755099040; c=relaxed/simple; bh=bMByBsrtjkN+fRggz+RI4RpCiPWZPkReGVAZTHbwDus=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XOW3CDieGwIIxW14h5gf+RyzlRfJPaF2tjzerBbziHqZ+UQ6U6gh2deabGD/Mly+qZoWtr3C4a4dfSqT6MPqTiQj+1cNQkGo1u5LAm84Iihmy22oxVXFhhv7L2Uo/THWM03cFsWv/tRz64O65Bl5GKZKvyAA0X6SeqUJPjdonWo= 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=X+NDqabR; arc=none smtp.client-ip=95.215.58.172 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="X+NDqabR" 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=1755099036; 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: in-reply-to:in-reply-to:references:references; bh=Fktp/IJNpxzdC2cRonL/xXN1tBsZHEP9YLQ3qx2TSgo=; b=X+NDqabRvfniiCccTSd3t4ZZDOcpusGOPzBCkOVbKlIdgawPJSUigdYc7wNieV6KzsET1d XJSll3iLlwKjzhwn9KUUZ4YaaE8TTQgIu1Kx5xfOUxhX8S8mhUhDIxDWGmN0SH6Q0X9SRB 5d/75mU93Rp/0IRv9QjmUbksV4f5NRs= 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, mykolal@fb.com, shuah@kernel.org, kafai.wan@linux.dev, mrpre@163.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: Felix Fietkau Subject: [PATCH bpf v2 1/2] bpf: Allow fall back to interpreter for programs with stack size <= 512 Date: Wed, 13 Aug 2025 23:29:57 +0800 Message-ID: <20250813152958.3107403-2-kafai.wan@linux.dev> In-Reply-To: <20250813152958.3107403-1-kafai.wan@linux.dev> References: <20250813152958.3107403-1-kafai.wan@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" OpenWRT users reported regression on ARMv6 devices after updating to latest HEAD, where tcpdump filter: tcpdump "not ether host 3c37121a2b3c and not ether host 184ecbca2a3a \ and not ether host 14130b4d3f47 and not ether host f0f61cf440b7 \ and not ether host a84b4dedf471 and not ether host d022be17e1d7 \ and not ether host 5c497967208b and not ether host 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=3Dy 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 =3D 1 2. "bpf: Avoid __bpf_prog_ret0_warn when jit fails" returns error when jit_requested =3D 1 but jit fails This change restores interpreter fallback capability for BPF programs with stack size <=3D 512 bytes when jit fails. Reported-by: Felix Fietkau Closes: https://lore.kernel.org/bpf/2e267b4b-0540-45d8-9310-e127bf95fc63@nb= d.name/ Fixes: 6ebc5030e0c5 ("bpf: Fix array bounds error with may_goto") Signed-off-by: KaFai Wan --- kernel/bpf/core.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 5d1650af899d..f8f8ac3b5513 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2366,8 +2366,7 @@ 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! + * is not working properly, so warn about it! */ WARN_ON_ONCE(1); return 0; @@ -2468,8 +2467,9 @@ static int bpf_check_tail_call(const struct bpf_prog = *fp) return ret; } =20 -static void bpf_prog_select_func(struct bpf_prog *fp) +static bool bpf_prog_select_interpreter(struct bpf_prog *fp) { + bool select_interpreter =3D false; #ifndef CONFIG_BPF_JIT_ALWAYS_ON u32 stack_depth =3D max_t(u32, fp->aux->stack_depth, 1); u32 idx =3D (round_up(stack_depth, 32) / 32) - 1; @@ -2478,15 +2478,16 @@ static void bpf_prog_select_func(struct bpf_prog *f= p) * But for non-JITed programs, we don't need bpf_func, so no bounds * check needed. */ - if (!fp->jit_requested && - !WARN_ON_ONCE(idx >=3D ARRAY_SIZE(interpreters))) { + if (idx < ARRAY_SIZE(interpreters)) { fp->bpf_func =3D interpreters[idx]; + select_interpreter =3D true; } else { fp->bpf_func =3D __bpf_prog_ret0_warn; } #else fp->bpf_func =3D __bpf_prog_ret0_warn; #endif + return select_interpreter; } =20 /** @@ -2505,7 +2506,7 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_p= rog *fp, int *err) /* In case of BPF to BPF calls, verifier did all the prep * work with regards to JITing, etc. */ - bool jit_needed =3D fp->jit_requested; + bool jit_needed =3D false; =20 if (fp->bpf_func) goto finalize; @@ -2514,7 +2515,8 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_p= rog *fp, int *err) bpf_prog_has_kfunc_call(fp)) jit_needed =3D true; =20 - bpf_prog_select_func(fp); + if (!bpf_prog_select_interpreter(fp)) + jit_needed =3D true; =20 /* eBPF JITs can rewrite the program in case constant * blinding is active. However, in case of error during --=20 2.43.0