[PATCH] arm: fix integer overflow in ELF_ET_DYN_BASE

Russell King - ARM Linux linux at arm.linux.org.uk
Thu Mar 26 08:05:58 PDT 2015

On Fri, Mar 20, 2015 at 02:12:52PM +0300, Andrey Ryabinin wrote:
> Usually ELF_ET_DYN_BASE is 2/3 of TASK_SIZE. With 3G/1G user/kernel
> split this is not so, because 2*TASK_SIZE overflows 32 bits,
> so the actual value of ELF_ET_DYN_BASE is:
> 	(2 * TASK_SIZE / 3) = 0x2a000000
> When ASLR is disabled PIE binaries will load at ELF_ET_DYN_BASE address.
> On 32bit platforms AddressSanitzer uses addresses [0x20000000 - 0x40000000]
> for shadow memory [1]. So ASan doesn't work for PIE binaries when ASLR disabled
> as it fails to map shadow memory.
> Also after Kees's 'split ET_DYN ASLR from mmap ASLR' patchset PIE binaries
> has a high chance of loading somewhere in between [0x2a000000 - 0x40000000]
> even if ASLR enabled. This makes ASan with PIE absolutely incompatible.
> Fix overflow by dividing TASK_SIZE prior to multiplying.
> After this patch ELF_ET_DYN_BASE equals to (for CONFIG_VMSPLIT_3G=y):
> 	(TASK_SIZE / 3 * 2) = 0x7f555554
> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm#Mapping
> Signed-off-by: Andrey Ryabinin <a.ryabinin at samsung.com>
> Reported-by: Maria Guseva <m.guseva at samsung.com>
> Cc: stable at vger.kernel.org

Who's handling this patch?  I'm guessing it should be me, so if it could
find its way into my patch system for when I next apply a bunch of patches,
that'd be good.


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