| From e575a86fdc50d013bf3ad3aa81d9100e8e6cc60d Mon Sep 17 00:00:00 2001 |
| From: Kees Cook <keescook@chromium.org> |
| Date: Thu, 7 Feb 2013 09:44:13 -0800 |
| Subject: x86: Do not leak kernel page mapping locations |
| |
| From: Kees Cook <keescook@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@gmail.com> |
| Suggested-by: Brad Spengler <spender@grsecurity.net> |
| Signed-off-by: Kees Cook <keescook@chromium.org> |
| Acked-by: H. Peter Anvin <hpa@zytor.com> |
| Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| Cc: Frederic Weisbecker <fweisbec@gmail.com> |
| Cc: Eric W. Biederman <ebiederm@xmission.com> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Andrew Morton <akpm@linux-foundation.org> |
| Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> |
| Link: http://lkml.kernel.org/r/20130207174413.GA12485@www.outflux.net |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/mm/fault.c | 8 +++++--- |
| 1 file changed, 5 insertions(+), 3 deletions(-) |
| |
| --- a/arch/x86/mm/fault.c |
| +++ b/arch/x86/mm/fault.c |
| @@ -748,13 +748,15 @@ __bad_area_nosemaphore(struct pt_regs *r |
| 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); |