[PATCH 74/81] x86: Do not leak kernel page mapping locations
Herton Ronaldo Krzesinski
herton.krzesinski at canonical.com
Tue Feb 19 18:49:37 UTC 2013
3.5.7.6 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook <keescook at chromium.org>
commit e575a86fdc50d013bf3ad3aa81d9100e8e6cc60d upstream.
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 at gmail.com>
Suggested-by: Brad Spengler <spender at grsecurity.net>
Signed-off-by: Kees Cook <keescook at chromium.org>
Acked-by: H. Peter Anvin <hpa at zytor.com>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Eric W. Biederman <ebiederm at xmission.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra at chello.nl>
Link: http://lkml.kernel.org/r/20130207174413.GA12485@www.outflux.net
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
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 76dcd9d..c6b10e2 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -747,13 +747,15 @@ __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);
--
1.7.9.5
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