From patchwork Sun Dec 17 13:17:14 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Menglong Dong X-Patchwork-Id: 13495856 X-Patchwork-Delegate: bpf@iogearbox.net Received: from mail-il1-f196.google.com (mail-il1-f196.google.com [209.85.166.196]) (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 2853F4438A; Sun, 17 Dec 2023 13:18:35 +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="AfeBzLBP" Received: by mail-il1-f196.google.com with SMTP id e9e14a558f8ab-35f96476fb3so10853075ab.0; Sun, 17 Dec 2023 05:18:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1702819115; x=1703423915; 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=AfeBzLBP3Ji4QAVi7lLUbh9DM76OXM6lmJCPMv/nq/ui33zvH/NHOAYYkUOU2adLMm 5TtmtbZxIZmT3eCCzTEeX0QrLXZTngNvghJKdx9A3IOmePv9m8Tnm7Ogm9XcEcEtShDY lgjETwE497tF72SXO1S6Upyl8G4att9TP1ryfAj9/N+mFw49+wx9FuvzG7JYd2ZgekkW XhIh407i6PHBjZS9UFercvjiBuZVdw3OLQnbS3uS8w53pOUrrA00Pfs3kJw4jlddMRMo T73g8wHb2TdKJLcZPWNAf2J9CBis307DalPQ3iqKDbyhA23R0rVIi3OOA4W00xQ1JPVF wizA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702819115; x=1703423915; 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=Apj/4407NcEw7wXwuOv3pG/98AzDKtiLFWdZ5PiJPiiw47wI6o5488E1Bc91HCHgwT c6l9ZT8r8qNHiBNQKj9st0YjfsHeKSLrPRT4rgLjyXc8yzZ3+1semDPmg4y2S3J7/8Ia UH9poOJd27/e5kBdGpvFWpf3eiTgAnvkqijOIUJQ65TYAF4Za4cJLu33UWo+uhV7D4QT +Isf74+vqbTBmBSteLxV/kgDiktSQbCGpGiSyNEWNV18fZO5rPHiXv3Oum//E0gQ+7+t YdOvqnJDbjNHZe3RPsJDHcwdIBRJzyl1WkumL922XX866ZuEkCg1P4Zj1GHFa8vsPLal k03g== X-Gm-Message-State: AOJu0YwViGd36lOCWnSiB/Y0iolbFFxi7EBLJ4wBuzreZ2h3xaclS7HC zurKVkalfQzLY2u5fxncSLo= X-Google-Smtp-Source: AGHT+IFuYVYqCJXnlGSY0RyODewiiUKWPVJpKtwtNSLuGT8b2gpJNCbkzwTNT0Y1LI2TQsPuyAjZBA== X-Received: by 2002:a05:6e02:1a64:b0:35d:87d4:938c with SMTP id w4-20020a056e021a6400b0035d87d4938cmr23751297ilv.15.1702819115079; Sun, 17 Dec 2023 05:18:35 -0800 (PST) Received: from localhost.localdomain ([43.129.244.20]) by smtp.gmail.com with ESMTPSA id h10-20020a170902f7ca00b001d395d3df30sm1099425plw.130.2023.12.17.05.18.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 17 Dec 2023 05:18:34 -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, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Menglong Dong , Shung-Hsi Yu Subject: [PATCH bpf-next v4 1/3] bpf: make the verifier tracks the "not equal" for regs Date: Sun, 17 Dec 2023 21:17:14 +0800 Message-Id: <20231217131716.830290-2-menglong8.dong@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231217131716.830290-1-menglong8.dong@gmail.com> References: <20231217131716.830290-1-menglong8.dong@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net 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))