From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933272AbcFPAbB (ORCPT ); Wed, 15 Jun 2016 20:31:01 -0400 Received: from mail.kernel.org ([198.145.29.136]:50548 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964814AbcFPA2t (ORCPT ); Wed, 15 Jun 2016 20:28:49 -0400 From: Andy Lutomirski To: "linux-kernel@vger.kernel.org" , x86@kernel.org, Borislav Petkov Cc: Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Josh Poimboeuf , Andy Lutomirski Subject: [PATCH 08/13] x86/dumpstack: When OOPSing, rewind the stack before do_exit Date: Wed, 15 Jun 2016 17:28:30 -0700 Message-Id: <4e7adb96a576c6ff12d6cc2a972b2bf44ed2319a.1466036668.git.luto@kernel.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we call do_exit with a clean stack, we greatly reduce the risk of recursive oopses due to stack overflow in do_exit, and we allow do_exit to work even if we OOPS from an IST stack. The latter gives us a much better chance of surviving long enough after we detect a stack overflow to write out our logs. I intentionally separated this from the preceding patch that disables do_exit-on-OOPS on IST stacks. This way, if we need to revert this patch, we still end up in an acceptable state wrt stack overflow handling. Signed-off-by: Andy Lutomirski --- arch/x86/entry/entry_32.S | 11 +++++++++++ arch/x86/entry/entry_64.S | 11 +++++++++++ arch/x86/kernel/dumpstack.c | 13 +++++++++---- 3 files changed, 31 insertions(+), 4 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 983e5d3a0d27..1499db695a88 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -1153,3 +1153,14 @@ ENTRY(async_page_fault) jmp error_code END(async_page_fault) #endif + +ENTRY(rewind_stack_do_exit) + /* Prevent any naive code from trying to unwind to our caller. */ + xorl %ebp, %ebp + + movl PER_CPU_VAR(cpu_current_top_of_stack), %esi + leal -TOP_OF_KERNEL_STACK_PADDING-PT_OLDSS(%esi), %esp + + call do_exit +1: jmp 1b +END(rewind_stack_do_exit) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 9ee0da1807ed..394cad73e890 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1423,3 +1423,14 @@ ENTRY(ignore_sysret) mov $-ENOSYS, %eax sysret END(ignore_sysret) + +ENTRY(rewind_stack_do_exit) + /* Prevent any naive code from trying to unwind to our caller. */ + xorl %ebp, %ebp + + movq PER_CPU_VAR(cpu_current_top_of_stack), %rax + leaq -TOP_OF_KERNEL_STACK_PADDING-SS(%rax), %rsp + + call do_exit +1: jmp 1b +END(rewind_stack_do_exit) diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 36effb39c9c9..d4d085e27d04 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -228,6 +228,8 @@ unsigned long oops_begin(void) EXPORT_SYMBOL_GPL(oops_begin); NOKPROBE_SYMBOL(oops_begin); +extern void __noreturn rewind_stack_do_exit(int signr); + void oops_end(unsigned long flags, struct pt_regs *regs, int signr) { if (regs && kexec_should_crash(current)) @@ -247,12 +249,15 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr) return; if (in_interrupt()) panic("Fatal exception in interrupt"); - if (((current_stack_pointer() ^ (current_top_of_stack() - 1)) - & ~(THREAD_SIZE - 1)) != 0) - panic("Fatal exception on special stack"); if (panic_on_oops) panic("Fatal exception"); - do_exit(signr); + + /* + * We're not going to return, but we might be on an IST stack or + * have very little stack space left. Rewind the stack and kill + * the task. + */ + rewind_stack_do_exit(signr); } NOKPROBE_SYMBOL(oops_end); -- 2.7.4