From patchwork Tue Dec 13 03:04:35 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hao Sun X-Patchwork-Id: 13071681 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC885C00145 for ; Tue, 13 Dec 2022 03:05:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234078AbiLMDF3 (ORCPT ); Mon, 12 Dec 2022 22:05:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60248 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234371AbiLMDF3 (ORCPT ); Mon, 12 Dec 2022 22:05:29 -0500 Received: from mail-pf1-x42d.google.com (mail-pf1-x42d.google.com [IPv6:2607:f8b0:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15FA9193C4; Mon, 12 Dec 2022 19:05:28 -0800 (PST) Received: by mail-pf1-x42d.google.com with SMTP id c7so1271338pfc.12; Mon, 12 Dec 2022 19:05:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=KRz1ndE/MNsp7SX3z6xwVJjSnJS8PPptEfHAdy5xitk=; b=q65PtU/OnLz+25mz/mVduCl7jZSDJoi13dQGQCSLvKN6GODR3uguXnhLQdv64ym6ug 2CiBmWcQvAVY61gDaXEcwOvcnIopxaMjVJf9bw/QNxSdwU9/vyOS94qbtedEnYwfSqUS Dgcxvo1fuzXWetK1aqanQvhe3ztc3ndXlB2iL5bij7uBGg5r11fmxarVmolhHJKtJzoC biQz7tgeNJ5Oh8MGB1hrvekudjKcLwP1/C7sIKiF2k6Wm6DAUZJGZz312gzayZeP5Day 0C6+SUQnX5eU1nLTyboJNGnmrfryy+2+NMIN7UDPPCYrynbbYH32qoAXA1uHmyD/bcqR M0tw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=KRz1ndE/MNsp7SX3z6xwVJjSnJS8PPptEfHAdy5xitk=; b=y92Vb/KTgXhS66HEAt6XpgkSJpcDFiw7BxbcKwJ9IBGLDSYlevHhFvuz9NNuB538SY x3JqQD5U7vc9Bd+xsrJjfWHk8uq0H2GvBOOH+fpObolNsKTjLtPWEzjh4QskMJFkIy92 +TB1XSr8lrE6+xj55f8DCCkDF3O4BVIq4P7DMpKiUu3z51/ls3SnuMxrRFm6wxr8VQtF x5MY2tvDRf1kUqemnE+y4/WtaRHHfKQ9VBo0SOVl1Rx0Z9y+wfzbwvFnz27D3Odlfbwg TYY457MjCN/3loPQSrMm8K90VFN+WzFE4aieMtuHEbGVJi00poG+nq+tQ3+rC91FMxEM FycQ== X-Gm-Message-State: ANoB5pkDC60OjXwi3RRmuzhuRR5UhdAu+C/ylGhY8iy02HdzTSoVtb6w XoBIOES2ptM4c1R+FtOCBvKPrH69viID X-Google-Smtp-Source: AA0mqf60HvpiWuMtdGpFxMGaEMw6MLrEfv3EMwJJyC1YK2MysYXIUBp3Qxxkw7wxC7yYsMmFJ+ycZA== X-Received: by 2002:a62:3247:0:b0:574:7015:5501 with SMTP id y68-20020a623247000000b0057470155501mr19666643pfy.5.1670900727267; Mon, 12 Dec 2022 19:05:27 -0800 (PST) Received: from localhost.localdomain ([144.214.0.6]) by smtp.gmail.com with ESMTPSA id z21-20020aa79495000000b005746c3b2445sm6481716pfk.151.2022.12.12.19.05.24 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 12 Dec 2022 19:05:26 -0800 (PST) From: Hao Sun To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, davem@davemloft.net, linux-kernel@vger.kernel.org, Hao Sun Subject: [PATCH bpf-next v2 1/2] bpf: fix nullness propagation for reg to reg comparisons Date: Tue, 13 Dec 2022 11:04:35 +0800 Message-Id: <20221213030436.17907-1-sunhao.th@gmail.com> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net After befae75856ab, the verifier would propagate null information after JEQ/JNE, e.g., if two pointers, one is maybe_null and the other is not, the former would be marked as non-null in eq path. However, as comment "PTR_TO_BTF_ID points to a kernel struct that does not need to be null checked by the BPF program ... The verifier must keep this in mind and can make no assumptions about null or non-null when doing branch ...". If one pointer is maybe_null and the other is PTR_TO_BTF, the former is incorrectly marked non-null. The following BPF prog can trigger a null-ptr-deref, also see this report for more details[1]: 0: (18) r1 = map_fd ; R1_w=map_ptr(ks=4, vs=4) 2: (79) r6 = *(u64 *)(r1 +8) ; R6_w=bpf_map->inner_map_data ; R6 is PTR_TO_BTF_ID ; equals to null at runtime 3: (bf) r2 = r10 4: (07) r2 += -4 5: (62) *(u32 *)(r2 +0) = 0 6: (85) call bpf_map_lookup_elem#1 ; R0_w=map_value_or_null 7: (1d) if r6 == r0 goto pc+1 8: (95) exit ; from 7 to 9: R0=map_value R6=ptr_bpf_map 9: (61) r0 = *(u32 *)(r0 +0) ; null-ptr-deref 10: (95) exit So, make the verifier propagate nullness information for reg to reg comparisons only if neither reg is PTR_TO_BTF_ID. [1] https://lore.kernel.org/bpf/CACkBjsaFJwjC5oiw-1KXvcazywodwXo4zGYsRHwbr2gSG9WcSw@mail.gmail.com/T/#u Fixes: befae75856ab4 ("bpf: propagate nullness information for reg to reg comparisons") Signed-off-by: Hao Sun Acked-by: Yonghong Song --- kernel/bpf/verifier.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) base-commit: ef3911a3e4d65d2db617366e79517b896045a6e2 diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a5255a0dcbb6..243d06ce6842 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11822,10 +11822,17 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, * register B - not null * for JNE A, B, ... - A is not null in the false branch; * for JEQ A, B, ... - A is not null in the true branch. + * + * Since PTR_TO_BTF_ID points to a kernel struct that does + * not need to be null checked by the BPF program, i.e., + * could be null even without PTR_MAYBE_NULL marking, so + * only propagate nullness when neither reg is that type. */ if (!is_jmp32 && BPF_SRC(insn->code) == BPF_X && __is_pointer_value(false, src_reg) && __is_pointer_value(false, dst_reg) && - type_may_be_null(src_reg->type) != type_may_be_null(dst_reg->type)) { + type_may_be_null(src_reg->type) != type_may_be_null(dst_reg->type) && + base_type(src_reg->type) != PTR_TO_BTF_ID && + base_type(dst_reg->type) != PTR_TO_BTF_ID) { eq_branch_regs = NULL; switch (opcode) { case BPF_JEQ: