linux-kernel - [tip:x86/urgent] x86: Do not leak kernel page mapping locations

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Date:	Fri, 8 Feb 2013 06:05:14 -0800
From:	tip-bot for Kees Cook <keescook@...omium.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	a.p.zijlstra@...llo.nl, torvalds@...ux-foundation.org,
	ebiederm@...ssion.com, dan.j.rosenberg@...il.com,
	spender@...ecurity.net, paulmck@...ux.vnet.ibm.com,
	keescook@...omium.org, fweisbec@...il.com,
	akpm@...ux-foundation.org, tglx@...utronix.de
Subject: [tip:x86/urgent] x86: Do not leak kernel page mapping locations

Commit-ID:  e575a86fdc50d013bf3ad3aa81d9100e8e6cc60d
Gitweb:     http://git.kernel.org/tip/e575a86fdc50d013bf3ad3aa81d9100e8e6cc60d
Author:     Kees Cook <keescook@...omium.org>
AuthorDate: Thu, 7 Feb 2013 09:44:13 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 7 Feb 2013 19:57:44 +0100

x86: Do not leak kernel page mapping locations

Without this patch, it is trivial to determine kernel page
mappings by examining the error code reported to dmesg[1].
Instead, declare the entire kernel memory space as a violation
of a present page.

Additionally, since show_unhandled_signals is enabled by
default, switch branch hinting to the more realistic
expectation, and unobfuscate the setting of the PF_PROT bit to
improve readability.

[1] http://vulnfactory.org/blog/2013/02/06/a-linux-memory-trick/

Reported-by: Dan Rosenberg <dan.j.rosenberg@...il.com>
Suggested-by: Brad Spengler <spender@...ecurity.net>
Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: stable@...r.kernel.org
Acked-by: H. Peter Anvin <hpa@...or.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/20130207174413.GA12485@www.outflux.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/fault.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 027088f..fb674fd 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -748,13 +748,15 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 				return;
 		}
 #endif
+		/* Kernel addresses are always protection faults: */
+		if (address >= TASK_SIZE)
+			error_code |= PF_PROT;
 
-		if (unlikely(show_unhandled_signals))
+		if (likely(show_unhandled_signals))
 			show_signal_msg(regs, error_code, address, tsk);
 
-		/* Kernel addresses are always protection faults: */
 		tsk->thread.cr2		= address;
-		tsk->thread.error_code	= error_code | (address >= TASK_SIZE);
+		tsk->thread.error_code	= error_code;
 		tsk->thread.trap_nr	= X86_TRAP_PF;
 
 		force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0);
--
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