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powerpc,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. Inspired by Daniel Micay's linux-hardened tree. Link: http://lkml.kernel.org/r/20170622200033.25714-4-riel@redhat.com Signed-off-by: Rik van Riel <riel@redhat.com> Reported-by: Florian Weimer <fweimer@redhat.com> Cc: Ingo 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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commit
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1 changed files with 19 additions and 9 deletions
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@ -34,16 +34,9 @@
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/*
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* Top of mmap area (just below the process stack).
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*
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* Leave at least a ~128 MB hole on 32bit applications.
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*
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* On 64bit applications we randomise the stack by 1GB so we need to
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* space our mmap start address by a further 1GB, otherwise there is a
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* chance the mmap area will end up closer to the stack than our ulimit
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* requires.
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* Leave at least a ~128 MB hole.
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*/
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#define MIN_GAP32 (128*1024*1024)
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#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
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#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
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#define MIN_GAP (128*1024*1024)
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#define MAX_GAP (TASK_SIZE/6*5)
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static inline int mmap_is_legacy(void)
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@ -71,9 +64,26 @@ unsigned long arch_mmap_rnd(void)
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return rnd << PAGE_SHIFT;
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}
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static inline unsigned long stack_maxrandom_size(void)
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{
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if (!(current->flags & PF_RANDOMIZE))
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return 0;
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/* 8MB for 32bit, 1GB for 64bit */
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if (is_32bit_task())
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return (1<<23);
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else
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return (1<<30);
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}
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static inline unsigned long mmap_base(unsigned long rnd)
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{
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unsigned long gap = rlimit(RLIMIT_STACK);
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unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
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/* Values close to RLIM_INFINITY can overflow. */
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if (gap + pad > gap)
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gap += pad;
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if (gap < MIN_GAP)
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gap = MIN_GAP;
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