From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f50.google.com (mail-wm1-f50.google.com [209.85.128.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3CB4E306768 for ; Tue, 7 Jul 2026 07:17:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783408656; cv=none; b=P0hHKB7qNxJJHDky1gj8zqDdmTjCfJGm+bbpvJnz4dOqoUkR4xH4J77iEIryOH6xseMn5ivhFYIm85fL3/zrVF30j9ImPP8u+ZOpF+jhia6c1gE6rUdYPJWqP/IvNw3cIppyd5z8bTK3T7jN7gNxxpLFuQwjkOClCoezuNBba74= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783408656; c=relaxed/simple; bh=Ej8NqPpY8Y2tM5iaL7Pfew4r5IbWYX63UJqTgnJNTMQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DuiiHYP8BmkcMEK84dPwWTSXOq41kCyToa63/2f1yJ55ehVdEbGJ/n4zuag4BnTaXJthn3Fwa6LlLAG3snJ1uPXjypOKbecjkHnZgOksTZOkCrLgCYgO0pH0lBm4aemEWVLSTMujCuY6qD3yIiA0cmzUHObcYjjMtDMdchY2R3I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=SdaKDsbe; arc=none smtp.client-ip=209.85.128.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="SdaKDsbe" Received: by mail-wm1-f50.google.com with SMTP id 5b1f17b1804b1-493c486f012so15886775e9.3 for ; Tue, 07 Jul 2026 00:17:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1783408649; x=1784013449; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=l02n0V7uxUW1ka2kHMZJ3uiSZxCig+R49GpTVh1FrvI=; b=SdaKDsbePCNLu3pALbshc74sY9wTXoIKsDAGmAUyTmdZ31BfNU4oie/LpIJ3HQUf62 5JEsQOhuKy2wIzgmEIit37eHuesoJGCWnOdl7wh/FJ3grEB2UQgMbEydiMqumGfr6I2G 7E/WhEq2CP4/bM6E2bhQtishLMjg68ltxlNniYy6a4qZ7SFG/EEz9yP77GoIkIpiDeK8 Jp0rZNQ6w+j2C7lPj4ZQWktfcnODktzJ4g0rCTrlaHCS5j7SV9qzre1DjlNhALfdBmJZ NpooLELMwen2/eN9leOHd/yRqj79IxQpEepY/Ab2q9uEegB6NI4WeLbCpRwwKW602WJ0 tyGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1783408649; x=1784013449; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=l02n0V7uxUW1ka2kHMZJ3uiSZxCig+R49GpTVh1FrvI=; b=N7es49aask4NUQnnYVwL6V0IcmGKM3Gx9pWZh5QX70BWuF5Zi/OcmAAJGYAO/hVCNK xANb0DvVJM3XECtQrXeCswLuSvqsUDkszkzfv2CTjwB7+yOsx2MvGOYk0THTpIx28shT /s/woYnugQfHB7HXxG0+Gx8JPd/ItIH7wOgy49D2X+lMXQaVQf0mxywGFyZfdkVtudPX YTU9xRme4GavHu4QIddL9ETHmBCcSxtOceBfvUaKX2LMjSTn0roswr+lugl+Lb6WvAv9 DQXjFAHeWi9HnmzPdjrBT3WSG+0FhLEygaSxvovQ6LOWuLAb4zs7LvEtI/ogs2HNJfv0 4GDg== X-Forwarded-Encrypted: i=1; AHgh+RqIh0rlTXo8sYfgCuRKcAFUWWYdq20XnpFbl7R1XFU4Y+3Bl9eVwCNWpcmCKuVTU0YjymoEbKc7iiIOiVs=@vger.kernel.org X-Gm-Message-State: AOJu0Yw/95DfFKC+gYFWrVgIyiJWgYoHe0QTS5CH9XvGXvahlJmy5ZAr sfHC4OYZ0+FryJ1K4lWhrMB3lM35W5eiW6IbN71PTr54jbrzP/ncZBlLaflxfV0dj9g= X-Gm-Gg: AfdE7clOwZPuPQNqle1c7Kwy5wheFIlgWQ+X0vnM4SscHE5buwSISTsUeNTf8Y/zo4v 7Puu1VmCgB1V1CPGXCNTMzTV5bw6x2AbI28zl9ElUP+wjYwOwRq3Ic2Y3+PqJYynGw9te322psP rtsUge5YplxEsnvgrJpHKfeiruvwreJ6FTZosWoRNWKkZldupeRjWlU5AHG9/hWeVL6QvT+5InM RdjToLaAVIoejCHYs7sIWhvxFiNYpNPa4s0RtI8NwyGwcu/D8STyXSSB2aB2tf2sinEUqFljiT+ bQ2uFmD0aKmGKZdMm33HHp1cstzpU0zbwUf/lLBX1A925zEg0EftUOH0bAjBPQEzzWuyDJ7eu9Q nOx6MeIyA7dOpjKHQTocovrYDnaLgaweVx0E3bMGlX0goN8GdZ8eTq5kX3UCX7I5BUOBs4IMn01 y5/4NH8xjynFtnAwqR8yPmsZMeEwI/uU9q8R+KWSpqIvJA8g== X-Received: by 2002:a05:600c:5288:b0:490:b2c9:e284 with SMTP id 5b1f17b1804b1-493df09608emr41741795e9.30.1783408648684; Tue, 07 Jul 2026 00:17:28 -0700 (PDT) Received: from u94a (27-53-112-249.adsl.fetnet.net. [27.53.112.249]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc9bdb7e9sm6828225ad.10.2026.07.07.00.17.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2026 00:17:26 -0700 (PDT) Date: Tue, 7 Jul 2026 15:17:16 +0800 From: Shung-Hsi Yu To: Sun Jian Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, shuah@kernel.org, mmullins@fb.com, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH bpf v2 1/2] bpf: Reject negative const offsets for buffer pointers Message-ID: References: <20260707060804.93561-1-sun.jian.kdev@gmail.com> <20260707060804.93561-2-sun.jian.kdev@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260707060804.93561-2-sun.jian.kdev@gmail.com> Sorry I missed that there was a v2 already. Reposting the comments I sent to v1 below. On Mon, Jul 06, 2026 at 11:08:03PM -0700, Sun Jian wrote: [...] > @@ -5344,6 +5348,29 @@ static int __check_buffer_access(struct bpf_verifier_env *env, > return -EACCES; > } > > + var_off = (s64)reg->var_off.value; > + if (check_add_overflow(var_off, (s64)off, &start)) { > + verbose(env, > + "%s invalid %s buffer access: off=%d, var_off=%lld\n", > + reg_arg_name(env, argno), buf_info, off, var_off); > + return -EACCES; > + } Other pointer offset checks (check_mem_region_access and adjust_ptr_min_max_vals) seem to check var_off against BPF_MAX_VAR_OFF, and that `off` being >= 0. It would be great if the convention can be kept for consistency, albeit being more conservative. >From a blind guess I would guess that compiler does not product a pattern where `off` encoded in the instruction is negative but the net overall offset is positive for PTR_TO_TP_BUFFER/PTR_TO_BUF, and rejecting such pattern is fine. r6 = *(u64 *)(r1 + 0); r6 += 16; r0 = *(u64 *)(r6 - 8); One more comment below. > + > + if (start < 0) { > + verbose(env, > + "%s invalid negative %s buffer offset: off=%d, var_off=%lld\n", > + reg_arg_name(env, argno), buf_info, off, var_off); > + return -EACCES; > + } > + > + if (start > U32_MAX || size < 0 || > + check_add_overflow((u32)start, (u32)size, access_end)) { > + verbose(env, > + "%s invalid %s buffer access: off=%lld, size=%d\n", > + reg_arg_name(env, argno), buf_info, start, size); > + return -EACCES; > + } If we check that var_off is within BPF_MAX_VAR_OFF and that `off` is not negative, then `var_off + off + size` should be guaranteed to not overflow max_tp_access, since the maximum of `off` is S16_MAX and the maximum of `size` is 8. > + > return 0; > } > [...]