From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933922AbbENOUK (ORCPT ); Thu, 14 May 2015 10:20:10 -0400 Received: from mail-wg0-f42.google.com ([74.125.82.42]:33506 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933507AbbENOT7 (ORCPT ); Thu, 14 May 2015 10:19:59 -0400 From: Anisse Astier Cc: Anisse Astier , Andrew Morton , Mel Gorman , "Kirill A. Shutemov" , David Rientjes , Alan Cox , Linus Torvalds , Peter Zijlstra , PaX Team , Brad Spengler , Kees Cook , Andi Kleen , "Rafael J. Wysocki" , Pavel Machek , Len Brown , linux-mm@kvack.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 2/3] mm/page_alloc.c: add config option to sanitize freed pages Date: Thu, 14 May 2015 16:19:47 +0200 Message-Id: <1431613188-4511-3-git-send-email-anisse@astier.eu> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1431613188-4511-1-git-send-email-anisse@astier.eu> References: <1431613188-4511-1-git-send-email-anisse@astier.eu> To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This new config option will sanitize all freed pages. This is a pretty low-level change useful to track some cases of use-after-free, help kernel same-page merging in VM environments, and counter a few info leaks. Signed-off-by: Anisse Astier --- mm/Kconfig | 12 ++++++++++++ mm/page_alloc.c | 12 ++++++++++++ 2 files changed, 24 insertions(+) diff --git a/mm/Kconfig b/mm/Kconfig index 390214d..e9fb3bd 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -635,3 +635,15 @@ config MAX_STACK_SIZE_MB changed to a smaller value in which case that is used. A sane initial value is 80 MB. + +config SANITIZE_FREED_PAGES + bool "Sanitize memory pages after free" + default n + help + This option is used to make sure all pages freed are zeroed. This is + quite low-level and doesn't handle your slab buffers. + It has various applications, from preventing some info leaks to + helping kernel same-page merging in virtualised environments. + Depending on your workload it will greatly reduce performance. + + If unsure, say N. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4d5ce6e..c29e3a0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -795,6 +795,12 @@ static bool free_pages_prepare(struct page *page, unsigned int order) debug_check_no_obj_freed(page_address(page), PAGE_SIZE << order); } + +#ifdef CONFIG_SANITIZE_FREED_PAGES + for (i = 0; i < (1 << order); i++) + clear_highpage(page + i); +#endif + arch_free_page(page, order); kernel_map_pages(page, 1 << order, 0); @@ -960,9 +966,15 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, kernel_map_pages(page, 1 << order, 1); kasan_alloc_pages(page, order); +#ifndef CONFIG_SANITIZE_FREED_PAGES + /* SANITIZE_FREED_PAGES relies implicitly on the fact that pages are + * cleared before use, so we don't need gfp zero in the default case + * because all pages go through the free_pages_prepare code path when + * switching from bootmem to the default allocator */ if (gfp_flags & __GFP_ZERO) for (i = 0; i < (1 << order); i++) clear_highpage(page + i); +#endif if (order && (gfp_flags & __GFP_COMP)) prep_compound_page(page, order); -- 1.9.3