From patchwork Tue Dec 19 13:47:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Menglong Dong X-Patchwork-Id: 756696 Received: from mail-oo1-f65.google.com (mail-oo1-f65.google.com [209.85.161.65]) (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 F3D871A58F; Tue, 19 Dec 2023 13:50:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ioGokt/z" Received: by mail-oo1-f65.google.com with SMTP id 006d021491bc7-593d9b1139fso811752eaf.1; Tue, 19 Dec 2023 05:50:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1702993843; x=1703598643; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=vIG7gX50kKtmhzIyeXshzVLZolIi3kTx5IiKTBxlLu0=; b=ioGokt/z7J9mHNSSlfnrNpmaKq6ggDsV2EvsOMhhnH2kulZcbIPnsixNNwOt7VKBtS 6VNgVkRNPrhBiMquVeRkt298IJJFpCtjWj9qmPRsnH+6PIEXzdEJh25DfXB9zwQA8Ru8 uhbsa9mBGCB93E4dhKNReE6k7ykx+9RIvN3N3DLzsf0DqplqQAvlMuURIVnkHdtIJ00c TIOplV+/fnG/fK0MBMIsRyr5+E3n9uGO0AyYx49nDV3S+DeT484jemClgYr2ynNJcmMN zWMm9jpfNlBQB1Xaqw6HPCCyCh+ofOwn7YxpGEM9vimrw8ZLFuFw2QFCoyOKDWgPFySf Fgfw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702993843; x=1703598643; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=vIG7gX50kKtmhzIyeXshzVLZolIi3kTx5IiKTBxlLu0=; b=EVmr7XrIFAmA+X0m1Bw9MVAwnEtYhhV1KF8MRTDYwrI0IQq3yiVoBAJUP1wXRJhlYF F/s5xLY+0y2AbbYXMawxZ2D1RWD+n2DV8FWOAksP4CJ14zUvib1VPUoKjz70/3grvKik t5g0QT/p2GDKC26FCDE/wQEtpJ/vv4jn3rj31OD6FVxx4Y6XCqD/1LyMM1FhCrPiAaKG IjmwlAxO4QY00W3qjY838h9Ojtoz9MCfkBXl3m+h+G+htINmq3xoJ2en7mWK37P1O9Ix 9zpY06TJ/4mTqVyF7Ph4yY9+NhfQi4iBt7l9ppjVXL0rboqZdVzt8OnxD4/djPECE+NP dCnw== X-Gm-Message-State: AOJu0YzFWdFcsR7we6t7W7zJcQWh0UQt0aE7KMSUasuQD3sJ6uVnO/gQ qUfyA7D+Xtdw2HXtkosp4ic33NXVI/xihEFx X-Google-Smtp-Source: AGHT+IEUwCFelS+UDCF6zIJzpNrzXI5jANkHv2yAjuwZIR0y0E6j5IOFn16FRHcI6Z86VT3MRtmB8w== X-Received: by 2002:a05:6358:5e15:b0:170:b07b:8352 with SMTP id q21-20020a0563585e1500b00170b07b8352mr17482631rwn.4.1702993842987; Tue, 19 Dec 2023 05:50:42 -0800 (PST) Received: from localhost.localdomain ([43.129.244.20]) by smtp.gmail.com with ESMTPSA id d17-20020a056a00245100b006cddecbf432sm20695264pfj.96.2023.12.19.05.50.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Dec 2023 05:50:42 -0800 (PST) From: Menglong Dong To: andrii@kernel.org, eddyz87@gmail.com, yonghong.song@linux.dev, alexei.starovoitov@gmail.com Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, martin.lau@linux.dev, song@kernel.org, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, shuah@kernel.org, menglong8.dong@gmail.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Shung-Hsi Yu Subject: [PATCH bpf-next v5 1/4] bpf: make the verifier tracks the "not equal" for regs Date: Tue, 19 Dec 2023 21:47:57 +0800 Message-Id: <20231219134800.1550388-2-menglong8.dong@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231219134800.1550388-1-menglong8.dong@gmail.com> References: <20231219134800.1550388-1-menglong8.dong@gmail.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 We can derive some new information for BPF_JNE in regs_refine_cond_op(). Take following code for example: /* The type of "a" is u32 */ if (a > 0 && a < 100) { /* the range of the register for a is [0, 99], not [1, 99], * and will cause the following error: * * invalid zero-sized read * * as a can be 0. */ bpf_skb_store_bytes(skb, xx, xx, a, 0); } In the code above, "a > 0" will be compiled to "jmp xxx if a == 0". In the TRUE branch, the dst_reg will be marked as known to 0. However, in the fallthrough(FALSE) branch, the dst_reg will not be handled, which makes the [min, max] for a is [0, 99], not [1, 99]. For BPF_JNE, we can reduce the range of the dst reg if the src reg is a const and is exactly the edge of the dst reg. Signed-off-by: Menglong Dong Acked-by: Andrii Nakryiko Acked-by: Shung-Hsi Yu --- v2: - fix a typo in the subject - add some comments, as Eduard advised --- kernel/bpf/verifier.c | 38 +++++++++++++++++++++++++++++++++++++- 1 file changed, 37 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1863826a4ac3..29c41d66ea6f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14343,7 +14343,43 @@ static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state } break; case BPF_JNE: - /* we don't derive any new information for inequality yet */ + if (!is_reg_const(reg2, is_jmp32)) + swap(reg1, reg2); + if (!is_reg_const(reg2, is_jmp32)) + break; + + /* try to recompute the bound of reg1 if reg2 is a const and + * is exactly the edge of reg1. + */ + val = reg_const_value(reg2, is_jmp32); + if (is_jmp32) { + /* u32_min_value is not equal to 0xffffffff at this point, + * because otherwise u32_max_value is 0xffffffff as well, + * in such a case both reg1 and reg2 would be constants, + * jump would be predicted and reg_set_min_max() won't + * be called. + * + * Same reasoning works for all {u,s}{min,max}{32,64} cases + * below. + */ + if (reg1->u32_min_value == (u32)val) + reg1->u32_min_value++; + if (reg1->u32_max_value == (u32)val) + reg1->u32_max_value--; + if (reg1->s32_min_value == (s32)val) + reg1->s32_min_value++; + if (reg1->s32_max_value == (s32)val) + reg1->s32_max_value--; + } else { + if (reg1->umin_value == (u64)val) + reg1->umin_value++; + if (reg1->umax_value == (u64)val) + reg1->umax_value--; + if (reg1->smin_value == (s64)val) + reg1->smin_value++; + if (reg1->smax_value == (s64)val) + reg1->smax_value--; + } break; case BPF_JSET: if (!is_reg_const(reg2, is_jmp32))