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 X-Spam-Level: X-Spam-Status: No, score=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EDF29C43381 for ; Wed, 6 Mar 2019 22:31:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C41C620842 for ; Wed, 6 Mar 2019 22:31:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727424AbfCFWbu (ORCPT ); Wed, 6 Mar 2019 17:31:50 -0500 Received: from terminus.zytor.com ([198.137.202.136]:35945 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727409AbfCFWbu (ORCPT ); Wed, 6 Mar 2019 17:31:50 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x26MV8Mc1911295 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Wed, 6 Mar 2019 14:31:08 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x26MV7r21911292; Wed, 6 Mar 2019 14:31:07 -0800 Date: Wed, 6 Mar 2019 14:31:07 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Jann Horn Message-ID: Cc: bp@alien8.de, yamada.masahiro@socionext.com, linux-kernel@vger.kernel.org, jpoimboe@redhat.com, tglx@linutronix.de, jannh@google.com, akpm@linux-foundation.org, hpa@zytor.com, mingo@kernel.org, syzbot+ca95b2b7aef9e7cbd6ab@syzkaller.appspotmail.com, michal.lkml@markovi.net Reply-To: linux-kernel@vger.kernel.org, jannh@google.com, hpa@zytor.com, yamada.masahiro@socionext.com, bp@alien8.de, jpoimboe@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org, michal.lkml@markovi.net, syzbot+ca95b2b7aef9e7cbd6ab@syzkaller.appspotmail.com, mingo@kernel.org In-Reply-To: <20190301031201.7416-1-jannh@google.com> References: <20190301031201.7416-1-jannh@google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/unwind: Handle NULL pointer calls better in frame unwinder Git-Commit-ID: f4f34e1b82eb4219d8eaa1c7e2e17ca219a6a2b5 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: f4f34e1b82eb4219d8eaa1c7e2e17ca219a6a2b5 Gitweb: https://git.kernel.org/tip/f4f34e1b82eb4219d8eaa1c7e2e17ca219a6a2b5 Author: Jann Horn AuthorDate: Fri, 1 Mar 2019 04:12:00 +0100 Committer: Thomas Gleixner CommitDate: Wed, 6 Mar 2019 23:03:26 +0100 x86/unwind: Handle NULL pointer calls better in frame unwinder When the frame unwinder is invoked for an oops caused by a call to NULL, it currently skips the parent function because BP still points to the parent's stack frame; the (nonexistent) current function only has the first half of a stack frame, and BP doesn't point to it yet. Add a special case for IP==0 that calculates a fake BP from SP, then uses the real BP for the next frame. Note that this handles first_frame specially: Return information about the parent function as long as the saved IP is >=first_frame, even if the fake BP points below it. With an artificially-added NULL call in prctl_set_seccomp(), before this patch, the trace is: Call Trace: ? prctl_set_seccomp+0x3a/0x50 __x64_sys_prctl+0x457/0x6f0 ? __ia32_sys_prctl+0x750/0x750 do_syscall_64+0x72/0x160 entry_SYSCALL_64_after_hwframe+0x44/0xa9 After this patch, the trace is: Call Trace: prctl_set_seccomp+0x3a/0x50 __x64_sys_prctl+0x457/0x6f0 ? __ia32_sys_prctl+0x750/0x750 do_syscall_64+0x72/0x160 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Signed-off-by: Jann Horn Signed-off-by: Thomas Gleixner Acked-by: Josh Poimboeuf Cc: Borislav Petkov Cc: Andrew Morton Cc: syzbot Cc: "H. Peter Anvin" Cc: Masahiro Yamada Cc: Michal Marek Cc: linux-kbuild@vger.kernel.org Link: https://lkml.kernel.org/r/20190301031201.7416-1-jannh@google.com --- arch/x86/include/asm/unwind.h | 6 ++++++ arch/x86/kernel/unwind_frame.c | 25 ++++++++++++++++++++++--- 2 files changed, 28 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h index 1f86e1b0a5cd..499578f7e6d7 100644 --- a/arch/x86/include/asm/unwind.h +++ b/arch/x86/include/asm/unwind.h @@ -23,6 +23,12 @@ struct unwind_state { #elif defined(CONFIG_UNWINDER_FRAME_POINTER) bool got_irq; unsigned long *bp, *orig_sp, ip; + /* + * If non-NULL: The current frame is incomplete and doesn't contain a + * valid BP. When looking for the next frame, use this instead of the + * non-existent saved BP. + */ + unsigned long *next_bp; struct pt_regs *regs; #else unsigned long *sp; diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index 3dc26f95d46e..9b9fd4826e7a 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -320,10 +320,14 @@ bool unwind_next_frame(struct unwind_state *state) } /* Get the next frame pointer: */ - if (state->regs) + if (state->next_bp) { + next_bp = state->next_bp; + state->next_bp = NULL; + } else if (state->regs) { next_bp = (unsigned long *)state->regs->bp; - else + } else { next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp); + } /* Move to the next frame if it's safe: */ if (!update_stack_state(state, next_bp)) @@ -398,6 +402,21 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, bp = get_frame_pointer(task, regs); + /* + * If we crash with IP==0, the last successfully executed instruction + * was probably an indirect function call with a NULL function pointer. + * That means that SP points into the middle of an incomplete frame: + * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we + * would have written a frame pointer if we hadn't crashed. + * Pretend that the frame is complete and that BP points to it, but save + * the real BP so that we can use it when looking for the next frame. + */ + if (regs && regs->ip == 0 && + (unsigned long *)kernel_stack_pointer(regs) >= first_frame) { + state->next_bp = bp; + bp = ((unsigned long *)kernel_stack_pointer(regs)) - 1; + } + /* Initialize stack info and make sure the frame data is accessible: */ get_stack_info(bp, state->task, &state->stack_info, &state->stack_mask); @@ -410,7 +429,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, */ while (!unwind_done(state) && (!on_stack(&state->stack_info, first_frame, sizeof(long)) || - state->bp < first_frame)) + (state->next_bp == NULL && state->bp < first_frame))) unwind_next_frame(state); } EXPORT_SYMBOL_GPL(__unwind_start);