From patchwork Tue Feb 19 18:49:37 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [74/81] x86: Do not leak kernel page mapping locations Date: Tue, 19 Feb 2013 08:49:37 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 222070 Message-Id: <1361299784-8830-75-git-send-email-herton.krzesinski@canonical.com> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Kees Cook , Frederic Weisbecker , "Eric W. Biederman" , Andrew Morton , "Paul E. McKenney" , Linus Torvalds , Ingo Molnar , Peter Zijlstra 3.5.7.6 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Kees Cook 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 Suggested-by: Brad Spengler Signed-off-by: Kees Cook 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 Signed-off-by: Herton Ronaldo Krzesinski --- 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);