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Commit e575a86f authored by Kees Cook's avatar Kees Cook Committed by Ingo Molnar
Browse files

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: default avatarDan Rosenberg <dan.j.rosenberg@gmail.com>
Suggested-by: default avatarBrad Spengler <spender@grsecurity.net>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Acked-by: default avatarH. 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: default avatarIngo Molnar <mingo@kernel.org>
parent bb9b1a83

arch/x86/mm/fault.c

+5 −3
Original line number Diff line number Diff line
@@ -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);