From: Kees Cook Date: Thu, 7 Feb 2013 17:44:13 +0000 (-0800) Subject: x86: Do not leak kernel page mapping locations X-Git-Tag: v3.8~11^2~3 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=e575a86fdc50d013bf3ad3aa81d9100e8e6cc60d;p=platform%2Fkernel%2Flinux-amlogic.git 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 Suggested-by: Brad Spengler Signed-off-by: Kees Cook Cc: stable@vger.kernel.org Acked-by: H. Peter Anvin Cc: Paul E. McKenney Cc: Frederic Weisbecker Cc: Eric W. Biederman Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20130207174413.GA12485@www.outflux.net Signed-off-by: Ingo Molnar --- 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);