From patchwork Fri Nov 10 00:26:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 13451929 X-Patchwork-Delegate: bpf@iogearbox.net Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 56C087F for ; Fri, 10 Nov 2023 00:26:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0D242590 for ; Thu, 9 Nov 2023 16:26:52 -0800 (PST) Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 3A9MYB4Q013857 for ; Thu, 9 Nov 2023 16:26:52 -0800 Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3u7w3e41de-5 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 09 Nov 2023 16:26:52 -0800 Received: from twshared29562.14.frc2.facebook.com (2620:10d:c085:208::f) by mail.thefacebook.com (2620:10d:c085:11d::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.34; Thu, 9 Nov 2023 16:26:50 -0800 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id 5E6653B3FA047; Thu, 9 Nov 2023 16:26:41 -0800 (PST) From: Andrii Nakryiko To: , , , CC: , , Eduard Zingerman , Hao Sun Subject: [PATCH v2 bpf 1/3] bpf: handle ldimm64 properly in check_cfg() Date: Thu, 9 Nov 2023 16:26:36 -0800 Message-ID: <20231110002638.4168352-2-andrii@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231110002638.4168352-1-andrii@kernel.org> References: <20231110002638.4168352-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-ORIG-GUID: oix62ApR5aQRuV1VLSELPjNe8_7cGeeS X-Proofpoint-GUID: oix62ApR5aQRuV1VLSELPjNe8_7cGeeS X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-09_17,2023-11-09_01,2023-05-22_02 X-Patchwork-Delegate: bpf@iogearbox.net ldimm64 instructions are 16-byte long, and so have to be handled appropriately in check_cfg(), just like the rest of BPF verifier does. This has implications in three places: - when determining next instruction for non-jump instructions; - when determining next instruction for callback address ldimm64 instructions (in visit_func_call_insn()); - when checking for unreachable instructions, where second half of ldimm64 is expected to be unreachable; We take this also as an opportunity to report jump into the middle of ldimm64. And adjust few test_verifier tests accordingly. Acked-by: Eduard Zingerman Reported-by: Hao Sun Fixes: 475fb78fbf48 ("bpf: verifier (add branch/goto checks)") Signed-off-by: Andrii Nakryiko --- include/linux/bpf.h | 8 ++++-- kernel/bpf/verifier.c | 27 ++++++++++++++----- .../testing/selftests/bpf/verifier/ld_imm64.c | 8 +++--- 3 files changed, 30 insertions(+), 13 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index b4825d3cdb29..35bff17396c0 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -909,10 +909,14 @@ bpf_ctx_record_field_size(struct bpf_insn_access_aux *aux, u32 size) aux->ctx_field_size = size; } +static bool bpf_is_ldimm64(const struct bpf_insn *insn) +{ + return insn->code == (BPF_LD | BPF_IMM | BPF_DW); +} + static inline bool bpf_pseudo_func(const struct bpf_insn *insn) { - return insn->code == (BPF_LD | BPF_IMM | BPF_DW) && - insn->src_reg == BPF_PSEUDO_FUNC; + return bpf_is_ldimm64(insn) && insn->src_reg == BPF_PSEUDO_FUNC; } struct bpf_prog_ops { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index bd1c42eb540f..b87715b364fd 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -15439,15 +15439,16 @@ static int visit_func_call_insn(int t, struct bpf_insn *insns, struct bpf_verifier_env *env, bool visit_callee) { - int ret; + int ret, insn_sz; - ret = push_insn(t, t + 1, FALLTHROUGH, env, false); + insn_sz = bpf_is_ldimm64(&insns[t]) ? 2 : 1; + ret = push_insn(t, t + insn_sz, FALLTHROUGH, env, false); if (ret) return ret; - mark_prune_point(env, t + 1); + mark_prune_point(env, t + insn_sz); /* when we exit from subprog, we need to record non-linear history */ - mark_jmp_point(env, t + 1); + mark_jmp_point(env, t + insn_sz); if (visit_callee) { mark_prune_point(env, t); @@ -15469,15 +15470,17 @@ static int visit_func_call_insn(int t, struct bpf_insn *insns, static int visit_insn(int t, struct bpf_verifier_env *env) { struct bpf_insn *insns = env->prog->insnsi, *insn = &insns[t]; - int ret, off; + int ret, off, insn_sz; if (bpf_pseudo_func(insn)) return visit_func_call_insn(t, insns, env, true); /* All non-branch instructions have a single fall-through edge. */ if (BPF_CLASS(insn->code) != BPF_JMP && - BPF_CLASS(insn->code) != BPF_JMP32) - return push_insn(t, t + 1, FALLTHROUGH, env, false); + BPF_CLASS(insn->code) != BPF_JMP32) { + insn_sz = bpf_is_ldimm64(insn) ? 2 : 1; + return push_insn(t, t + insn_sz, FALLTHROUGH, env, false); + } switch (BPF_OP(insn->code)) { case BPF_EXIT: @@ -15607,11 +15610,21 @@ static int check_cfg(struct bpf_verifier_env *env) } for (i = 0; i < insn_cnt; i++) { + struct bpf_insn *insn = &env->prog->insnsi[i]; + if (insn_state[i] != EXPLORED) { verbose(env, "unreachable insn %d\n", i); ret = -EINVAL; goto err_free; } + if (bpf_is_ldimm64(insn)) { + if (insn_state[i + 1] != 0) { + verbose(env, "jump into the middle of ldimm64 insn %d\n", i); + ret = -EINVAL; + goto err_free; + } + i++; /* skip second half of ldimm64 */ + } } ret = 0; /* cfg looks good */ diff --git a/tools/testing/selftests/bpf/verifier/ld_imm64.c b/tools/testing/selftests/bpf/verifier/ld_imm64.c index f9297900cea6..78f19c255f20 100644 --- a/tools/testing/selftests/bpf/verifier/ld_imm64.c +++ b/tools/testing/selftests/bpf/verifier/ld_imm64.c @@ -9,8 +9,8 @@ BPF_MOV64_IMM(BPF_REG_0, 2), BPF_EXIT_INSN(), }, - .errstr = "invalid BPF_LD_IMM insn", - .errstr_unpriv = "R1 pointer comparison", + .errstr = "jump into the middle of ldimm64 insn 1", + .errstr_unpriv = "jump into the middle of ldimm64 insn 1", .result = REJECT, }, { @@ -23,8 +23,8 @@ BPF_LD_IMM64(BPF_REG_0, 1), BPF_EXIT_INSN(), }, - .errstr = "invalid BPF_LD_IMM insn", - .errstr_unpriv = "R1 pointer comparison", + .errstr = "jump into the middle of ldimm64 insn 1", + .errstr_unpriv = "jump into the middle of ldimm64 insn 1", .result = REJECT, }, { From patchwork Fri Nov 10 00:26:37 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 13451932 X-Patchwork-Delegate: bpf@iogearbox.net Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 7FBFC7F6 for ; Fri, 10 Nov 2023 00:27:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 204932D7C for ; Thu, 9 Nov 2023 16:27:00 -0800 (PST) Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 3A9MYCAY013908 for ; Thu, 9 Nov 2023 16:27:00 -0800 Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3u7w3e41dv-5 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 09 Nov 2023 16:26:59 -0800 Received: from twshared34392.14.frc2.facebook.com (2620:10d:c0a8:1c::11) by mail.thefacebook.com (2620:10d:c0a8:83::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.34; Thu, 9 Nov 2023 16:26:55 -0800 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id 6ABD13B3FA051; Thu, 9 Nov 2023 16:26:43 -0800 (PST) From: Andrii Nakryiko To: , , , CC: , , Eduard Zingerman Subject: [PATCH v2 bpf 2/3] bpf: fix precision backtracking instruction iteration Date: Thu, 9 Nov 2023 16:26:37 -0800 Message-ID: <20231110002638.4168352-3-andrii@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231110002638.4168352-1-andrii@kernel.org> References: <20231110002638.4168352-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-ORIG-GUID: atrgbvE3n5crgPHBiONGvkv7E9jsc3y2 X-Proofpoint-GUID: atrgbvE3n5crgPHBiONGvkv7E9jsc3y2 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-09_17,2023-11-09_01,2023-05-22_02 X-Patchwork-Delegate: bpf@iogearbox.net Fix an edge case in __mark_chain_precision() which prematurely stops backtracking instructions in a state if it happens that state's first and last instruction indexes are the same. This situations doesn't necessarily mean that there were no instructions simulated in a state, but rather that we starting from the instruction, jumped around a bit, and then ended up at the same instruction before checkpointing or marking precision. To distinguish between these two possible situations, we need to consult jump history. If it's empty or contain a single record "bridging" parent state and first instruction of processed state, then we indeed backtracked all instructions in this state. But if history is not empty, we are definitely not done yet. Move this logic inside get_prev_insn_idx() to contain it more nicely. Use -ENOENT return code to denote "we are out of instructions" situation. This bug was exposed by verifier_loop1.c's bounded_recursion subtest, once the next fix in this patch set is applied. Acked-by: Eduard Zingerman Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking") Signed-off-by: Andrii Nakryiko --- kernel/bpf/verifier.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b87715b364fd..484c742f733e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3516,12 +3516,29 @@ static int push_jmp_history(struct bpf_verifier_env *env, /* Backtrack one insn at a time. If idx is not at the top of recorded * history then previous instruction came from straight line execution. + * Return -ENOENT if we exhausted all instructions within given state. + * + * It's legal to have a bit of a looping with the same starting and ending + * insn index within the same state, e.g.: 3->4->5->3, so just because current + * instruction index is the same as state's first_idx doesn't mean we are + * done. If there is still some jump history left, we should keep going. We + * need to take into account that we might have a jump history between given + * state's parent and itself, due to checkpointing. In this case, we'll have + * history entry recording a jump from last instruction of parent state and + * first instruction of given state. */ static int get_prev_insn_idx(struct bpf_verifier_state *st, int i, u32 *history) { u32 cnt = *history; + if (i == st->first_insn_idx) { + if (cnt == 0) + return -ENOENT; + if (cnt == 1 && st->jmp_history[0].idx == i) + return -ENOENT; + } + if (cnt && st->jmp_history[cnt - 1].idx == i) { i = st->jmp_history[cnt - 1].prev_idx; (*history)--; @@ -4401,10 +4418,10 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno) * Nothing to be tracked further in the parent state. */ return 0; - if (i == first_idx) - break; subseq_idx = i; i = get_prev_insn_idx(st, i, &history); + if (i == -ENOENT) + break; if (i >= env->prog->len) { /* This can happen if backtracking reached insn 0 * and there are still reg_mask or stack_mask From patchwork Fri Nov 10 00:26:38 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 13451931 X-Patchwork-Delegate: bpf@iogearbox.net Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 5F470628 for ; Fri, 10 Nov 2023 00:26:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0A80830D1 for ; Thu, 9 Nov 2023 16:26:56 -0800 (PST) Received: from pps.filterd (m0109334.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 3A9MZAjP002443 for ; Thu, 9 Nov 2023 16:26:55 -0800 Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3u91swvhp1-6 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 09 Nov 2023 16:26:55 -0800 Received: from twshared68648.02.prn6.facebook.com (2620:10d:c085:108::8) by mail.thefacebook.com (2620:10d:c085:11d::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.34; Thu, 9 Nov 2023 16:26:53 -0800 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id 939303B3FA05D; Thu, 9 Nov 2023 16:26:45 -0800 (PST) From: Andrii Nakryiko To: , , , CC: , Subject: [PATCH v2 bpf 3/3] selftests/bpf: add edge case backtracking logic test Date: Thu, 9 Nov 2023 16:26:38 -0800 Message-ID: <20231110002638.4168352-4-andrii@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231110002638.4168352-1-andrii@kernel.org> References: <20231110002638.4168352-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: lHKsinznQMbm_Yyf_dL36kb9WwmGHoch X-Proofpoint-ORIG-GUID: lHKsinznQMbm_Yyf_dL36kb9WwmGHoch X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-09_17,2023-11-09_01,2023-05-22_02 X-Patchwork-Delegate: bpf@iogearbox.net Add a dedicated selftests to try to set up conditions to have a state with same first and last instruction index, but it actually is a loop 3->4->1->2->3. This confuses mark_chain_precision() if verifier doesn't take into account jump history. Signed-off-by: Andrii Nakryiko --- .../selftests/bpf/progs/verifier_precision.c | 40 +++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_precision.c b/tools/testing/selftests/bpf/progs/verifier_precision.c index 193c0f8272d0..6b564d4c0986 100644 --- a/tools/testing/selftests/bpf/progs/verifier_precision.c +++ b/tools/testing/selftests/bpf/progs/verifier_precision.c @@ -91,3 +91,43 @@ __naked int bpf_end_bswap(void) } #endif /* v4 instruction */ + +SEC("?raw_tp") +__success __log_level(2) +/* + * Without the bug fix there will be no history between "last_idx 3 first_idx 3" + * and "parent state regs=" lines. "R0_w=6" parts are here to help anchor + * expected log messages to the one specific mark_chain_precision operation. + * + * This is quite fragile: if verifier checkpointing heuristic changes, this + * might need adjusting. + */ +__msg("2: (07) r0 += 1 ; R0_w=6") +__msg("3: (35) if r0 >= 0xa goto pc+1") +__msg("mark_precise: frame0: last_idx 3 first_idx 3 subseq_idx -1") +__msg("mark_precise: frame0: regs=r0 stack= before 2: (07) r0 += 1") +__msg("mark_precise: frame0: regs=r0 stack= before 1: (07) r0 += 1") +__msg("mark_precise: frame0: regs=r0 stack= before 4: (05) goto pc-4") +__msg("mark_precise: frame0: regs=r0 stack= before 3: (35) if r0 >= 0xa goto pc+1") +__msg("mark_precise: frame0: parent state regs= stack=: R0_rw=P4") +__msg("3: R0_w=6") +__naked int state_loop_first_last_equal(void) +{ + asm volatile ( + "r0 = 0;" + "l0_%=:" + "r0 += 1;" + "r0 += 1;" + /* every few iterations we'll have a checkpoint here with + * first_idx == last_idx, potentially confusing precision + * backtracking logic + */ + "if r0 >= 10 goto l1_%=;" /* checkpoint + mark_precise */ + "goto l0_%=;" + "l1_%=:" + "exit;" + ::: __clobber_common + ); +} + +char _license[] SEC("license") = "GPL";