From e575a86fdc50d013bf3ad3aa81d9100e8e6cc60d Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 7 Feb 2013 09:44:13 -0800 Subject: 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 --- arch/x86/mm/fault.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'arch/x86/mm/fault.c') diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 027088f2f7dd..fb674fd3fc22 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); -- cgit v1.2.3 From 954f857187033ee3d3704a8206715cf354c38898 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Fri, 22 Feb 2013 15:11:49 -0800 Subject: Revert "x86, mm: Make spurious_fault check explicitly check explicitly check the PRESENT bit" I got a report for a minor regression introduced by commit 027ef6c87853b ("mm: thp: fix pmd_present for split_huge_page and PROT_NONE with THP"). So the problem is, pageattr creates kernel pagetables (pte and pmds) that breaks pte_present/pmd_present and the patch above exposed this invariant breakage for pmd_present. The same problem already existed for the pte and pte_present and it was fixed by commit 660a293ea9be709 ("x86, mm: Make spurious_fault check explicitly check the PRESENT bit") (if it wasn't for that commit, it wouldn't even be a regression). That fix avoids the pagefault to use pte_present. I could follow through by stopping using pmd_present/pmd_huge too. However I think it's more robust to fix pageattr and to clear the PSE/GLOBAL bitflags too in addition to the present bitflag. So the kernel page fault can keep using the regular pte_present/pmd_present/pmd_huge. The confusion arises because _PAGE_GLOBAL and _PAGE_PROTNONE are sharing the same bit, and in the pmd case we pretend _PAGE_PSE to be set only in present pmds (to facilitate split_huge_page final tlb flush). Signed-off-by: Andrea Arcangeli Cc: Andi Kleen Cc: Shaohua Li Cc: "H. Peter Anvin" Cc: Mel Gorman Cc: Hugh Dickins Cc: Andrew Morton Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar --- arch/x86/mm/fault.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) (limited to 'arch/x86/mm/fault.c') diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index fb674fd3fc22..2b97525246d4 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -939,14 +939,8 @@ spurious_fault(unsigned long error_code, unsigned long address) if (pmd_large(*pmd)) return spurious_fault_check(error_code, (pte_t *) pmd); - /* - * Note: don't use pte_present() here, since it returns true - * if the _PAGE_PROTNONE bit is set. However, this aliases the - * _PAGE_GLOBAL bit, which for kernel pages give false positives - * when CONFIG_DEBUG_PAGEALLOC is used. - */ pte = pte_offset_kernel(pmd, address); - if (!(pte_flags(*pte) & _PAGE_PRESENT)) + if (!pte_present(*pte)) return 0; ret = spurious_fault_check(error_code, pte); -- cgit v1.2.3