From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947233AbcHRNii (ORCPT ); Thu, 18 Aug 2016 09:38:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38389 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946924AbcHRNid (ORCPT ); Thu, 18 Aug 2016 09:38:33 -0400 From: Josh Poimboeuf To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Linus Torvalds , Steven Rostedt , Brian Gerst , Kees Cook , Peter Zijlstra , Frederic Weisbecker , Byungchul Park , Nilay Vaish Subject: [PATCH v4 09/57] x86/dumpstack: fix x86_32 kernel_stack_pointer() previous stack access Date: Thu, 18 Aug 2016 08:05:49 -0500 Message-Id: In-Reply-To: References: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 18 Aug 2016 13:06:56 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On x86_32, when an interrupt happens from kernel space, SS and SP aren't pushed and the existing stack is used. So pt_regs is effectively two words shorter, and the previous stack pointer is normally the memory after the shortened pt_regs, aka '®s->sp'. But in the rare case where the interrupt hits right after the stack pointer has been changed to point to an empty stack, like for example when call_on_stack() is used, the address immediately after the shortened pt_regs is no longer on the stack. In that case, instead of '®s->sp', the previous stack pointer should be retrieved from the beginning of the current stack page. kernel_stack_pointer() wants to do that, but it forgets to dereference the pointer. So instead of returning a pointer to the previous stack, it returns a pointer to the beginning of the current stack. Note that it's probably outside of kernel_stack_pointer()'s scope to be switching stacks at all. The x86_64 version of this function doesn't do it, and it would be better for the caller to do it if necessary. But that's a patch for another day. This just fixes the original intent. Fixes: 0788aa6a23cb ("x86: Prepare removal of previous_esp from i386 thread_info structure") Signed-off-by: Josh Poimboeuf --- arch/x86/kernel/ptrace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 2537cfb..5b88a1b 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -173,8 +173,8 @@ unsigned long kernel_stack_pointer(struct pt_regs *regs) return sp; prev_esp = (u32 *)(context); - if (prev_esp) - return (unsigned long)prev_esp; + if (*prev_esp) + return (unsigned long)*prev_esp; return (unsigned long)regs; } -- 2.7.4