Messages in this thread | | | Date | Sat, 21 Feb 2015 00:47:38 +0600 | Subject | Re: [PATCH] x86/compressed: remove unnecessary check | From | Alexander Kuleshov <> |
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Hello Kees,
yes you're fully right.
sorry for noise.
2015-02-21 0:38 GMT+06:00 Kees Cook <keescook@chromium.org>: > On Fri, Feb 20, 2015 at 9:55 AM, Alexander Kuleshov > <kuleshovmail@gmail.com> 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 <kuleshovmail@gmail.com> >> --- >> 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
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