From mboxrd@z Thu Jan 1 00:00:00 1970 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 96736C04A68 for ; Wed, 27 Jul 2022 21:01:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231338AbiG0VBq (ORCPT ); Wed, 27 Jul 2022 17:01:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231199AbiG0VBp (ORCPT ); Wed, 27 Jul 2022 17:01:45 -0400 Received: from mout02.posteo.de (mout02.posteo.de [185.67.36.66]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 65FFE5508C for ; Wed, 27 Jul 2022 14:01:44 -0700 (PDT) Received: from submission (posteo.de [185.67.36.169]) by mout02.posteo.de (Postfix) with ESMTPS id 59619240108 for ; Wed, 27 Jul 2022 23:01:42 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1658955702; bh=+D1UKSZRAHr0gs/2jxIHd9hWT5SDhWzM5/hoHGSsW8o=; h=Date:From:To:Cc:Subject:From; b=op3KGYx3WqT+dVO9Dtcq8zMviWOfoiqDLALmlMe5p2Le2YvyUZ3Fz0ZDqtQNuZ2Nd R+MTFk57JaXw/Paa9CWNulTsVb1dv/TZOmmgMu1Ht/DUWj7RWKc913v3RkXlsOtcjT gza/5N8E2nFJjD01sJ6rIY8OdWPnSQtgtKiyOOxZooNvkytNCmcuFHmu97u3ZQckLb N9zozw0lSOOvvr1ozpTZA+Rs1g54tP8RjfWpuPuKEFTYFX0EX63/2lrM8MF9RK69nR ItJn0Hw1w6fiEgwj5NjgiktEcY+VOoQYdUMI4AW4Qeuo7706W+pNR6SlAm3Yqdx+fZ 6P+i+7rX+mh6A== Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4LtR6D6YjNz9rxH; Wed, 27 Jul 2022 23:01:40 +0200 (CEST) Date: Wed, 27 Jul 2022 21:01:36 +0000 From: Daniel =?utf-8?Q?M=C3=BCller?= To: bpf@vger.kernel.org Cc: mhiramat@kernel.org, kernel-team@fb.com Subject: [BUG] kernel NULL pointer dereference in kprobe_int3_handler Message-ID: <20220727210136.jjgc3lpqeq42yr3m@muellerd-fedora-PC2BDTX9> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Hi, I've seen a NULL pointer dereference in kprobe_int3_handler, in code that seems to have gotten added with 6256e668b7af9 ("x86/kprobes: Use int3 instead of debug trap for single-step"). Specifically, our CI has reported the following (running test_progs-no_alu32): [ 1033.068258] test_progs-no_a[1177] is installing a program with bpf_probe_write_user helper that may corrupt user memory! [ 1040.264691] BUG: kernel NULL pointer dereference, address: 0000000000000058 [ 1040.264856] #PF: supervisor read access in kernel mode [ 1040.264890] #PF: error_code(0x0000) - not-present page [ 1040.264961] PGD 0 P4D 0 [ 1040.265183] Oops: 0000 [#1] PREEMPT SMP NOPTI [ 1040.265183] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W OE 5.19.0-rc7-g4129b786299d #1 [ 1040.265183] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 [ 1040.265183] RIP: 0010:kprobe_int3_handler+0xd4/0x1a0 [ 1040.265183] Code: 49 8b 06 48 83 e8 02 48 a9 fd ff ff ff 75 d0 48 c7 c7 32 cc 2b 82 e8 eb d5 9a 00 48 8b 95 80 00 00 00 65 48 8b 3d 74 62 fc 7e <48> 8b 47 58 48 39 d0 73 ac 48 8d 48 0f 48 39 ca 73 a3 48 8b 4f 28 [ 1040.265183] RSP: 0018:ffffb4140009bd40 EFLAGS: 00000092 [ 1040.265183] RAX: 0000000000000001 RBX: ffffffff81a04cb9 RCX: 0000000000000000 [ 1040.265183] RDX: ffffffff81a04cb9 RSI: ffffffff822bcc32 RDI: 0000000000000000 [ 1040.265183] RBP: ffffb4140009bd98 R08: 000000000003929b R09: 0000000000000000 [ 1040.265183] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 [ 1040.265183] R13: ffffffff81a04cb8 R14: ffff9490b9c5b1e0 R15: 0000000000000000 [ 1040.265183] FS: 0000000000000000(0000) GS:ffff9490b9c40000(0000) knlGS:0000000000000000 [ 1040.265183] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1040.265183] CR2: 0000000000000058 CR3: 0000000028836000 CR4: 00000000000006e0 [ 1040.265183] Call Trace: [ 1040.265183] [ 1040.265183] do_int3+0xf/0x50 [ 1040.265183] exc_int3+0x87/0xd0 [ 1040.265183] asm_exc_int3+0x35/0x40 [ 1040.265183] RIP: 0010:__schedule+0x3f9/0xbf0 [ 1040.265183] Code: 83 5a fe ff ff 65 ff 05 e5 61 61 7e 48 8b 05 3e cb 68 01 48 85 c0 74 16 48 8b 78 08 4c 89 f1 4c 89 ea 44 8b 45 ac 8b 75 b8 e8 <53> 6c 79 ff 65 ff 0d bc 61 61 7e 0f 85 0d fe ff ff e8 a0 cf 5f ff [ 1040.265183] RSP: 0018:ffffb4140009be70 EFLAGS: 00000086 [ 1040.265183] RAX: ffff9490056e0b90 RBX: ffff9490002f39e8 RCX: ffff949008758000 [ 1040.265183] RDX: ffff9490002f3300 RSI: 0000000000000000 RDI: 0000000000000000 [ 1040.265183] RBP: ffffb4140009bec8 R08: 0000000000000000 R09: 1dc944f200000000 [ 1040.265183] R10: 0000000000000001 R11: 0000000000080000 R12: ffff9490b9c6c8c0 [ 1040.265183] R13: ffff9490002f3300 R14: ffff949008758000 R15: ffff9490b9c6c8d8 [ 1040.265183] ? __schedule+0x3f9/0xbf0 [ 1040.265183] schedule_idle+0x26/0x40 [ 1040.265183] do_idle+0x177/0x250 [ 1040.265183] cpu_startup_entry+0x19/0x20 [ 1040.265183] start_secondary+0xed/0xf0 [ 1040.265183] secondary_startup_64_no_verify+0xe0/0xeb [ 1040.265183] [ 1040.265183] Modules linked in: bpf_testmod(OE) [last unloaded: bpf_testmod] [ 1040.265183] CR2: 0000000000000058 [ 1040.265183] ---[ end trace 0000000000000000 ]--- [ 1040.265183] RIP: 0010:kprobe_int3_handler+0xd4/0x1a0 [ 1040.265183] Code: 49 8b 06 48 83 e8 02 48 a9 fd ff ff ff 75 d0 48 c7 c7 32 cc 2b 82 e8 eb d5 9a 00 48 8b 95 80 00 00 00 65 48 8b 3d 74 62 fc 7e <48> 8b 47 58 48 39 d0 73 ac 48 8d 48 0f 48 39 ca 73 a3 48 8b 4f 28 [ 1040.265183] RSP: 0018:ffffb4140009bd40 EFLAGS: 00000092 [ 1040.265183] RAX: 0000000000000001 RBX: ffffffff81a04cb9 RCX: 0000000000000000 [ 1040.265183] RDX: ffffffff81a04cb9 RSI: ffffffff822bcc32 RDI: 0000000000000000 [ 1040.265183] RBP: ffffb4140009bd98 R08: 000000000003929b R09: 0000000000000000 [ 1040.265183] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 [ 1040.265183] R13: ffffffff81a04cb8 R14: ffff9490b9c5b1e0 R15: 0000000000000000 [ 1040.265183] FS: 0000000000000000(0000) GS:ffff9490b9c40000(0000) knlGS:0000000000000000 [ 1040.265183] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1040.265183] CR2: 0000000000000058 CR3: 0000000028836000 CR4: 00000000000006e0 [ 1040.265183] Kernel panic - not syncing: Fatal exception in interrupt [ 1040.265183] Kernel Offset: 0x0 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) (it was sync'ed to somewhere around 40b09653b1977 ("selftests/bpf: Adjust vmtest.sh to use local kernel configuration"); I can probably piece together the exact kernel configuration if needed, but the inquiry is of a more general nature) I am wondering what is the reason for us not checking whether kprobe_running returned a non-NULL pointer here (as we do elsewhere): https://elixir.bootlin.com/linux/v5.18.13/source/arch/x86/kernel/kprobes/core.c#L986 ? Is that an oversight or should some kind of invariant be upheld at this point? kprobe_int3_handler+0xd4/0x1a0 maps to line 987 in the above file. Address 0000000000000058 is exactly the offset that p->ainsn.insn is at, so it seems as if p is NULL. Thanks, Daniel