summaryrefslogtreecommitdiff
path: root/include
diff options
context:
space:
mode:
authorMel Gorman <mgorman@suse.de>2017-08-02 13:31:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-08-02 16:34:46 -0700
commit3ea277194daaeaa84ce75180ec7c7a2075027a68 (patch)
tree6feff56c07d2f273fc35e892a5ed5b1c99f9be00 /include
parent27e37d84e55f47bf28f7072fadf8fa2cbc3d9375 (diff)
mm, mprotect: flush TLB if potentially racing with a parallel reclaim leaving stale TLB entries
Nadav Amit identified a theoritical race between page reclaim and mprotect due to TLB flushes being batched outside of the PTL being held. He described the race as follows: CPU0 CPU1 ---- ---- user accesses memory using RW PTE [PTE now cached in TLB] try_to_unmap_one() ==> ptep_get_and_clear() ==> set_tlb_ubc_flush_pending() mprotect(addr, PROT_READ) ==> change_pte_range() ==> [ PTE non-present - no flush ] user writes using cached RW PTE ... try_to_unmap_flush() The same type of race exists for reads when protecting for PROT_NONE and also exists for operations that can leave an old TLB entry behind such as munmap, mremap and madvise. For some operations like mprotect, it's not necessarily a data integrity issue but it is a correctness issue as there is a window where an mprotect that limits access still allows access. For munmap, it's potentially a data integrity issue although the race is massive as an munmap, mmap and return to userspace must all complete between the window when reclaim drops the PTL and flushes the TLB. However, it's theoritically possible so handle this issue by flushing the mm if reclaim is potentially currently batching TLB flushes. Other instances where a flush is required for a present pte should be ok as either the page lock is held preventing parallel reclaim or a page reference count is elevated preventing a parallel free leading to corruption. In the case of page_mkclean there isn't an obvious path that userspace could take advantage of without using the operations that are guarded by this patch. Other users such as gup as a race with reclaim looks just at PTEs. huge page variants should be ok as they don't race with reclaim. mincore only looks at PTEs. userfault also should be ok as if a parallel reclaim takes place, it will either fault the page back in or read some of the data before the flush occurs triggering a fault. Note that a variant of this patch was acked by Andy Lutomirski but this was for the x86 parts on top of his PCID work which didn't make the 4.13 merge window as expected. His ack is dropped from this version and there will be a follow-on patch on top of PCID that will include his ack. [akpm@linux-foundation.org: tweak comments] [akpm@linux-foundation.org: fix spello] Link: http://lkml.kernel.org/r/20170717155523.emckq2esjro6hf3z@suse.de Reported-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: <stable@vger.kernel.org> [v4.4+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/mm_types.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ff151814a02d..7f384bb62d8e 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -495,6 +495,10 @@ struct mm_struct {
*/
bool tlb_flush_pending;
#endif
+#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
+ /* See flush_tlb_batched_pending() */
+ bool tlb_flush_batched;
+#endif
struct uprobes_state uprobes_state;
#ifdef CONFIG_HUGETLB_PAGE
atomic_long_t hugetlb_usage;