From fb754f958f8e46202c1efd7f66d5b3db1208117d Mon Sep 17 00:00:00 2001 From: Thomas Garnier Date: Tue, 9 Aug 2016 10:11:05 -0700 Subject: [PATCH] x86/mm/KASLR: Increase BRK pages for KASLR memory randomization Default implementation expects 6 pages maximum are needed for low page allocations. If KASLR memory randomization is enabled, the worse case of e820 layout would require 12 pages (no large pages). It is due to the PUD level randomization and the variable e820 memory layout. This bug was found while doing extensive testing of KASLR memory randomization on different type of hardware. Signed-off-by: Thomas Garnier Cc: Aleksey Makarov Cc: Andrew Morton Cc: Andy Lutomirski Cc: Baoquan He Cc: Borislav Petkov Cc: Borislav Petkov Cc: Brian Gerst Cc: Christian Borntraeger Cc: Dan Williams Cc: Dave Hansen Cc: Dave Young Cc: Denys Vlasenko Cc: Fabian Frederick Cc: H. Peter Anvin Cc: Joerg Roedel Cc: Josh Poimboeuf Cc: Kees Cook Cc: Linus Torvalds Cc: Lv Zheng Cc: Mark Salter Cc: Peter Zijlstra Cc: Rafael J . Wysocki Cc: Thomas Gleixner Cc: Toshi Kani Cc: kernel-hardening@lists.openwall.com Fixes: 021182e52fe0 ("Enable KASLR for physical mapping memory regions") Link: http://lkml.kernel.org/r/1470762665-88032-2-git-send-email-thgarnie@google.com Signed-off-by: Ingo Molnar --- arch/x86/mm/init.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index 6209289..d28a2d7 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -122,8 +122,18 @@ __ref void *alloc_low_pages(unsigned int num) return __va(pfn << PAGE_SHIFT); } -/* need 3 4k for initial PMD_SIZE, 3 4k for 0-ISA_END_ADDRESS */ -#define INIT_PGT_BUF_SIZE (6 * PAGE_SIZE) +/* + * By default need 3 4k for initial PMD_SIZE, 3 4k for 0-ISA_END_ADDRESS. + * With KASLR memory randomization, depending on the machine e820 memory + * and the PUD alignment. We may need twice more pages when KASLR memory + * randomization is enabled. + */ +#ifndef CONFIG_RANDOMIZE_MEMORY +#define INIT_PGD_PAGE_COUNT 6 +#else +#define INIT_PGD_PAGE_COUNT 12 +#endif +#define INIT_PGT_BUF_SIZE (INIT_PGD_PAGE_COUNT * PAGE_SIZE) RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE); void __init early_alloc_pgt_buf(void) { -- 2.7.4