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Commit c204d21f authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
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x86/mmap: properly account for stack randomization in mmap_base 

When RLIMIT_STACK is, for example, 256MB, the current code results in a
gap between the top of the task and mmap_base of 256MB, failing to take
into account the amount by which the stack address was randomized.  In
other words, the stack gets less than RLIMIT_STACK space.

Ensure that the gap between the stack and mmap_base always takes stack
randomization and the stack guard gap into account.

Obtained from Daniel Micay's linux-hardened tree.

Link: http://lkml.kernel.org/r/20170622200033.25714-2-riel@redhat.com


Signed-off-by: default avatarDaniel Micay <danielmicay@gmail.com>
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Reported-by: default avatarFlorian Weimer <fweimer@redhat.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2c8340ed

arch/x86/mm/mmap.c

+6 −1
Original line number Diff line number Diff line
@@ -92,13 +92,18 @@ unsigned long arch_mmap_rnd(void) 
static unsigned long mmap_base(unsigned long rnd, unsigned long task_size)

{

	unsigned long gap = rlimit(RLIMIT_STACK);

	unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;

	unsigned long gap_min, gap_max;



	/* Values close to RLIM_INFINITY can overflow. */

	if (gap + pad > gap)

		gap += pad;



	/*

	 * Top of mmap area (just below the process stack).

	 * Leave an at least ~128 MB hole with possible stack randomization.

	 */

	gap_min = SIZE_128M + stack_maxrandom_size(task_size);

	gap_min = SIZE_128M;

	gap_max = (task_size / 6) * 5;



	if (gap < gap_min)