Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932113AbbBTSrk (ORCPT ); Fri, 20 Feb 2015 13:47:40 -0500 Received: from mail-oi0-f44.google.com ([209.85.218.44]:54793 "EHLO mail-oi0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753936AbbBTSrj (ORCPT ); Fri, 20 Feb 2015 13:47:39 -0500 MIME-Version: 1.0 In-Reply-To: References: <1424454931-22428-1-git-send-email-kuleshovmail@gmail.com> Date: Sat, 21 Feb 2015 00:47:38 +0600 Message-ID: Subject: Re: [PATCH] x86/compressed: remove unnecessary check From: Alexander Kuleshov To: Kees Cook Cc: "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2291 Lines: 82 Hello Kees, yes you're fully right. sorry for noise. 2015-02-21 0:38 GMT+06:00 Kees Cook : > On Fri, Feb 20, 2015 at 9:55 AM, Alexander Kuleshov > wrote: >> region.start is entry->addr, but we already did check for case when >> entry->addr + entry->size < minimum, so no need to check that >> region.start is less than minimum. > > Nope, that's not correct. Those are separate checks. For example, a > region 20..130 would be seen as: > > start = 20 > size = 110 > > With minimum = 50, the first check eliminates anything with size <= 30 > (since the region would be entirely (20...50) below the minimum). > > The second check (the one you're suggesting to remove) raises the > bottom of the region up to the minimum: > > start = 50 > > And later on ("Reduce size by any delta from the original address."), > the size is also adjusted to notice any changes: > > size = 80 > > Now the region is 50...130: the bottom is cut off to adapt to the > minimum location. > > Is there some situation you found where this logic isn't working? > > -Kees > >> >> Signed-off-by: Alexander Kuleshov >> --- >> arch/x86/boot/compressed/aslr.c | 6 +----- >> 1 file changed, 1 insertion(+), 5 deletions(-) >> >> diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c >> index bb13763..13424a9 100644 >> --- a/arch/x86/boot/compressed/aslr.c >> +++ b/arch/x86/boot/compressed/aslr.c >> @@ -249,11 +249,7 @@ static void process_e820_entry(struct e820entry *entry, >> >> region.start = entry->addr; >> region.size = entry->size; >> - >> - /* Potentially raise address to minimum location. */ >> - if (region.start < minimum) >> - region.start = minimum; >> - >> + >> /* Potentially raise address to meet alignment requirements. */ >> region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN); >> >> -- >> 2.3.0.80.g18d0fec >> > > > > -- > Kees Cook > Chrome OS Security -- _________________________ 0xAX -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/