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=-16.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 2D6FFC43381 for ; Fri, 1 Mar 2019 03:12:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E268D20850 for ; Fri, 1 Mar 2019 03:12:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="jP76D9jq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729344AbfCADM0 (ORCPT ); Thu, 28 Feb 2019 22:12:26 -0500 Received: from mail-oi1-f201.google.com ([209.85.167.201]:49254 "EHLO mail-oi1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726088AbfCADMZ (ORCPT ); Thu, 28 Feb 2019 22:12:25 -0500 Received: by mail-oi1-f201.google.com with SMTP id a6so9916752oib.16 for ; Thu, 28 Feb 2019 19:12:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=hC9+KSqOfhghtXwTt0v7+bYNbD8DdeCfRg/HFFLJAeA=; b=jP76D9jqMpYrWUIxuvCrRMU2LZuPijnrnELxsec/YFtHPen/gOscyJjNR6FaFXdfTV LPaL/3zMF2wHLxfyNWrpCsL/w0ur1bdy3CSQpilJU2DRCpZlj4kdeif+0hUKTzKSsoE4 I3PdkXE7UsVUqXmvHD1wqHFAXAo4rkS6VCQ6tCT3kOpOPHvG3oxnPqVNNHXonB3HbHHc JPm5onXFDpgQ5BZnewQp5qU2knRNM1gH6wHPE4Wwr38yPqhO4cSrQaxSRzImh9J5qz6E tEO99MD34asSt2G2MnOwjqQz5JK6KeVwr7eiUv0q7J4cMnI6P/gZuta21QDiVXPfLawk qdvw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=hC9+KSqOfhghtXwTt0v7+bYNbD8DdeCfRg/HFFLJAeA=; b=nFgfB8yekLLIbj9Y5C7ndMilGM6XSTCAPpyMDgJBdeRO9ksKQjyFIv32jVanRU+TnC 5VEBCmSNOCO2Q48c3w6+wxuMhY6aBhaiylqgtlnqkkJLdGXkDrFnJkp+jEZ5Q2hISzlE WKNWE7C+UeHXnA0s0Ag0BokTmm567mtRFhmGPLdlGhiuhz4UIPFisB8/vg+jAAqlV02s pikgAnrWx5/GjbLAhQpcF6ddONTEQiZXbsXof82JVRqw6qirzTYnMwGZaUfY/42/vib8 kk915yD3P7m2TEUKXrHHAmAJHzmg4lRfqnW1LZ0y7+wC3OgdnSQZNAFy9kW7WHh5ujGb MPrg== X-Gm-Message-State: APjAAAWv4NUAxgXSvNFHO7F9cpfpXZ7Moz+bd7Re7k+Tl3KjwxgaDgZi BseEFcJZu9yIWg1nc80Ne1Qr3f2mxg== X-Google-Smtp-Source: APXvYqx90sayLEaLUXzAnkk0uNpBcBJvkWOJBKm6MkssnI+8gPtNlYjsdqc7YptM4tZ1fWJLA+PpAhfD/w== X-Received: by 2002:a05:6830:8b:: with SMTP id a11mr1703155oto.33.1551409944690; Thu, 28 Feb 2019 19:12:24 -0800 (PST) Date: Fri, 1 Mar 2019 04:12:00 +0100 Message-Id: <20190301031201.7416-1-jannh@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.21.0.352.gf09ad66450-goog Subject: [PATCH 1/2] x86/unwind: handle NULL pointer calls better in frame unwinder From: Jann Horn To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , jannh@google.com Cc: Andrew Morton , Josh Poimboeuf , syzbot , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Masahiro Yamada , Michal Marek , linux-kbuild@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: We 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 --- 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); -- 2.21.0.352.gf09ad66450-goog