From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751296AbdJDWkP (ORCPT ); Wed, 4 Oct 2017 18:40:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35476 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751182AbdJDWkO (ORCPT ); Wed, 4 Oct 2017 18:40:14 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 5BD4520B0C Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com Date: Wed, 4 Oct 2017 17:40:08 -0500 From: Josh Poimboeuf To: Tetsuo Handa Cc: fengguang.wu@intel.com, byungchul.park@lge.com, mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, lkp@01.org, torvalds@linux-foundation.org, bp@alien8.de, x86@kernel.org, hpa@zytor.com, tglx@linutronix.de Subject: Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer dereference at 000001f2 Message-ID: <20171004224008.3gbwuzn3zfwpidh3@treble> References: <20171003143147.ypotpg4f3dql4gtf@treble> <20171003144136.ar7z3pavhvizfabs@treble> <20171003150538.57dq7xe6afikpzyp@treble> <20171003162815.2eatamg4h3tpsypl@treble> <20171003173402.hq4aviy5hztgauyt@treble> <201710040644.GJE89219.FOHMFSFOVtOQLJ@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <201710040644.GJE89219.FOHMFSFOVtOQLJ@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 04 Oct 2017 22:40:14 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 04, 2017 at 06:44:50AM +0900, Tetsuo Handa wrote: > Josh Poimboeuf wrote: > > On Tue, Oct 03, 2017 at 11:28:15AM -0500, Josh Poimboeuf wrote: > > > There are two bugs: > > > > > > 1) Somebody -- presumably lockdep -- is corrupting the stack. Need the > > > lockdep people to look at that. > > > > > > 2) The 32-bit FP unwinder isn't handling the corrupt stack very well, > > > It's blindly dereferencing untrusted data: > > > > > > /* Is the next frame pointer an encoded pointer to pt_regs? */ > > > regs = decode_frame_pointer(next_bp); > > > if (regs) { > > > frame = (unsigned long *)regs; > > > len = regs_size(regs); > > > state->got_irq = true; > > > > > > On 32-bit, regs_size() dereferences the regs pointer before we know it > > > points to a valid stack. I'll fix that, along with the other unwinder > > > improvements I discussed with Linus. > > > > Tetsuo and/or Fengguang, > > > > Would you mind testing with this patch? It should at least prevent the > > unwinder panic and should hopefully print a useful unwinder dump > > instead. > > > Here are two outputs. Tetsuo, would you mind trying the following patch? diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 8a13d468635a..50e0d2bc4528 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -176,7 +176,7 @@ /* * This is a sneaky trick to help the unwinder find pt_regs on the stack. The * frame pointer is replaced with an encoded pointer to pt_regs. The encoding - * is just setting the LSB, which makes it an invalid stack address and is also + * is just clearing the MSB, which makes it an invalid stack address and is also * a signal to the unwinder that it's a pt_regs pointer in disguise. * * NOTE: This macro must be used *after* SAVE_ALL because it corrupts the @@ -185,7 +185,7 @@ .macro ENCODE_FRAME_POINTER #ifdef CONFIG_FRAME_POINTER mov %esp, %ebp - orl $0x1, %ebp + andl $0x7fffffff, %ebp #endif .endm diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index d145a0b1f529..acefab447f00 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -44,7 +44,8 @@ static void unwind_dump(struct unwind_state *state) state->stack_info.type, state->stack_info.next_sp, state->stack_mask, state->graph_idx); - for (sp = state->orig_sp; sp; sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) { + for (sp = PTR_ALIGN(state->orig_sp, sizeof(long)); sp; + sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) { if (get_stack_info(sp, state->task, &stack_info, &visit_mask)) break; @@ -77,6 +78,12 @@ static size_t regs_size(struct pt_regs *regs) return sizeof(*regs); } +#ifdef CONFIG_X86_32 +#define KERNEL_REGS_SIZE (sizeof(struct pt_regs) - 2*sizeof(long)) +#else +#define KERNEL_REGS_SIZE (sizeof(struct pt_regs)) +#endif + static bool in_entry_code(unsigned long ip) { char *addr = (char *)ip; @@ -174,6 +181,7 @@ static bool is_last_task_frame(struct unwind_state *state) * This determines if the frame pointer actually contains an encoded pointer to * pt_regs on the stack. See ENCODE_FRAME_POINTER. */ +#ifdef CONFIG_X86_64 static struct pt_regs *decode_frame_pointer(unsigned long *bp) { unsigned long regs = (unsigned long)bp; @@ -183,6 +191,17 @@ static struct pt_regs *decode_frame_pointer(unsigned long *bp) return (struct pt_regs *)(regs & ~0x1); } +#else +static struct pt_regs *decode_frame_pointer(unsigned long *bp) +{ + unsigned long regs = (unsigned long)bp; + + if (regs & 0x80000000) + return NULL; + + return (struct pt_regs *)(regs | 0x80000000); +} +#endif static bool update_stack_state(struct unwind_state *state, unsigned long *next_bp) @@ -202,7 +221,7 @@ static bool update_stack_state(struct unwind_state *state, regs = decode_frame_pointer(next_bp); if (regs) { frame = (unsigned long *)regs; - len = regs_size(regs); + len = KERNEL_REGS_SIZE; state->got_irq = true; } else { frame = next_bp; @@ -226,6 +245,14 @@ static bool update_stack_state(struct unwind_state *state, frame < prev_frame_end) return false; + /* + * On 32-bit with user mode regs, make sure the last two regs are safe + * to access: + */ + if (IS_ENABLED(CONFIG_X86_32) && regs && user_mode(regs) && + !on_stack(info, frame, len + 2*sizeof(long))) + return false; + /* Move state to the next frame: */ if (regs) { state->regs = regs;