From patchwork Mon Aug 12 21:48:47 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yonghong Song X-Patchwork-Id: 13761064 X-Patchwork-Delegate: bpf@iogearbox.net Received: from 66-220-155-178.mail-mxout.facebook.com (66-220-155-178.mail-mxout.facebook.com [66.220.155.178]) (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 A8B3B4D112 for ; Mon, 12 Aug 2024 21:49:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.155.178 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723499346; cv=none; b=NA0UjZy67xVZrpjRN8zziwdtf9xquqwERFcmd4A8kw2wtNg7CYWtY0/obbafzWMexb1yRcQxBojj491P2l5+d7xAXtjMo3ndKuR6G/Y0HFJcxPE7hqjCqvmj81kHjGDaRQD6RkY5nVY5//a6ctSlBetQYx+xAcu95oronGkyUqU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723499346; c=relaxed/simple; bh=eNPVlfchbyHdZzTWUMi0tPH99vYLTnh18h87Vot3/Ko=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Sr60Mlu1NJLsV2eBs6GdI+jvXLSnwMEOi0OpmR4JlqqOZZV1aVkCV/fIeEqsnJ9kYwrQRnnXKavQGhcDADw8kkgH1RF4eBaNtxrqQX9M9zbDdakBnSI8slnNf/ZjnhS85i5OLWxMcFhBKBZateIQz51K0E60ZGAdnfNpjPWpn7U= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=66.220.155.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devbig309.ftw3.facebook.com (Postfix, from userid 128203) id B7E117A9E9E6; Mon, 12 Aug 2024 14:48:47 -0700 (PDT) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com, Martin KaFai Lau , Eduard Zingerman , Daniel Hodges Subject: [PATCH bpf v2 1/2] bpf: Fix a kernel verifier crash in stacksafe() Date: Mon, 12 Aug 2024 14:48:47 -0700 Message-ID: <20240812214847.213612-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.43.5 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 Daniel Hodges reported a kernel verifier crash when playing with sched-ext. The crash dump looks like below: [ 65.874474] BUG: kernel NULL pointer dereference, address: 0000000000000088 [ 65.888406] #PF: supervisor read access in kernel mode [ 65.898682] #PF: error_code(0x0000) - not-present page [ 65.908957] PGD 0 P4D 0 [ 65.914020] Oops: 0000 [#1] SMP [ 65.920300] CPU: 19 PID: 9364 Comm: scx_layered Kdump: loaded Tainted: G S E 6.9.5-g93cea04637ea-dirty #7 [ 65.941874] Hardware name: Quanta Delta Lake MP 29F0EMA01D0/Delta Lake-Class1, BIOS F0E_3A19 04/27/2023 [ 65.960664] RIP: 0010:states_equal+0x3ee/0x770 [ 65.969559] Code: 33 85 ed 89 e8 41 0f 48 c7 83 e0 f8 89 e9 29 c1 48 63 c1 4c 89 e9 48 c1 e1 07 49 8d 14 08 0f b6 54 10 78 49 03 8a 58 05 00 00 <3a> 54 08 78 0f 85 60 03 00 00 49 c1 e5 07 43 8b 44 28 70 83 e0 03 [ 66.007120] RSP: 0018:ffffc9000ebeb8b8 EFLAGS: 00010202 [ 66.017570] RAX: 0000000000000000 RBX: ffff888149719680 RCX: 0000000000000010 [ 66.031843] RDX: 0000000000000000 RSI: ffff88907f4e0c08 RDI: ffff8881572f0000 [ 66.046115] RBP: 0000000000000000 R08: ffff8883d5014000 R09: ffffffff83065d50 [ 66.060386] R10: ffff8881bf9a1800 R11: 0000000000000002 R12: 0000000000000000 [ 66.074659] R13: 0000000000000000 R14: ffff888149719a40 R15: 0000000000000007 [ 66.088932] FS: 00007f5d5da96800(0000) GS:ffff88907f4c0000(0000) knlGS:0000000000000000 [ 66.105114] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 66.116606] CR2: 0000000000000088 CR3: 0000000388261001 CR4: 00000000007706f0 [ 66.130873] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 66.145145] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 66.159416] PKRU: 55555554 [ 66.164823] Call Trace: [ 66.169709] [ 66.173906] ? __die_body+0x66/0xb0 [ 66.180890] ? page_fault_oops+0x370/0x3d0 [ 66.189082] ? console_unlock+0xb5/0x140 [ 66.196926] ? exc_page_fault+0x4f/0xb0 [ 66.204597] ? asm_exc_page_fault+0x22/0x30 [ 66.212974] ? states_equal+0x3ee/0x770 [ 66.220643] ? states_equal+0x529/0x770 [ 66.228312] do_check+0x60f/0x5240 [ 66.235114] do_check_common+0x388/0x840 [ 66.242960] do_check_subprogs+0x101/0x150 [ 66.251150] bpf_check+0x5d5/0x4b60 [ 66.258134] ? __mod_memcg_state+0x79/0x110 [ 66.266506] ? pcpu_alloc+0x892/0xba0 [ 66.273829] bpf_prog_load+0x5bb/0x660 [ 66.281324] ? bpf_prog_bind_map+0x1e1/0x290 [ 66.289862] __sys_bpf+0x29d/0x3a0 [ 66.296664] __x64_sys_bpf+0x18/0x20 [ 66.303811] do_syscall_64+0x6a/0x140 [ 66.311133] entry_SYSCALL_64_after_hwframe+0x4b/0x53 Forther investigation shows that the crash is due to invalid memory access in stacksafe(). More specifically, it is the following code: if (exact != NOT_EXACT && old->stack[spi].slot_type[i % BPF_REG_SIZE] != cur->stack[spi].slot_type[i % BPF_REG_SIZE]) return false; If cur->allocated_stack is 0, cur->stack will be a ZERO_SIZE_PTR. If this happens, cur->stack[spi].slot_type[i % BPF_REG_SIZE] will crash the kernel as the memory address is illegal. This is exactly what happened in the above crash dump. If cur->allocated_stack is not 0, the above code could trigger array out-of-bound access. The patch added a condition 'i >= cur->allocated_stack' such that if the condition is true, stacksafe() should fail. Otherwise, cur->stack[spi].slot_type[i % BPF_REG_SIZE] memory access is always legal. Fixes: 2793a8b015f7 ("bpf: exact states comparison for iterator convergence checks") Cc: Eduard Zingerman Reported-by: Daniel Hodges Acked-by: Eduard Zingerman Signed-off-by: Yonghong Song --- kernel/bpf/verifier.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) Changelogs: v1 -> v2: - If 'i >= cur->allocated_stack' during !NOT_EXACT slot_type comparisoon, return false. diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4cb5441ad75f..d8520095ca03 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16884,8 +16884,9 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old, spi = i / BPF_REG_SIZE; if (exact != NOT_EXACT && - old->stack[spi].slot_type[i % BPF_REG_SIZE] != - cur->stack[spi].slot_type[i % BPF_REG_SIZE]) + (i >= cur->allocated_stack || + old->stack[spi].slot_type[i % BPF_REG_SIZE] != + cur->stack[spi].slot_type[i % BPF_REG_SIZE])) return false; if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ)