The patch titled Subject: mm, oom_reaper: gather each vma to prevent leaking TLB entry has been added to the -mm tree. Its filename is mm-oom_reaper-gather-each-vma-to-prevent-leaking-tlb-entry.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-oom_reaper-gather-each-vma-to-prevent-leaking-tlb-entry.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-oom_reaper-gather-each-vma-to-prevent-leaking-tlb-entry.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Wang Nan <wangnan0@xxxxxxxxxx> Subject: mm, oom_reaper: gather each vma to prevent leaking TLB entry tlb_gather_mmu(&tlb, mm, 0, -1) means gathering the whole virtual memory space. In this case, tlb->fullmm is true. Some archs like arm64 doesn't flush TLB when tlb->fullmm is true: commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1"). Which causes leaking of tlb entries. Will clarifies his patch: : Basically, we tag each address space with an ASID (PCID on x86) which : is resident in the TLB. This means we can elide TLB invalidation when : pulling down a full mm because we won't ever assign that ASID to another mm : without doing TLB invalidation elsewhere (which actually just nukes the : whole TLB). : : I think that means that we could potentially not fault on a kernel uaccess, : because we could hit in the TLB. There could be a window between complete_signal() sending IPI to other cores and all threads sharing this mm are really kicked off from cores. In this window, the oom reaper may calls tlb_flush_mmu_tlbonly() to flush TLB then frees pages. However, due to the above problem, the TLB entries are not really flushed on arm64. Other threads are possible to access these pages through TLB entries. Moreover, a copy_to_user() can also write to these pages without generating page fault, causes use-after-free bugs. This patch gathers each vma instead of gathering full vm space. In this case tlb->fullmm is not true. The behavior of oom reaper become similar to munmapping before do_exit, which should be safe for all archs. Link: http://lkml.kernel.org/r/20171107095453.179940-1-wangnan0@xxxxxxxxxx Fixes: aac453635549 ("mm, oom: introduce oom reaper") Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Bob Liu <liubo95@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/oom_kill.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff -puN mm/oom_kill.c~mm-oom_reaper-gather-each-vma-to-prevent-leaking-tlb-entry mm/oom_kill.c --- a/mm/oom_kill.c~mm-oom_reaper-gather-each-vma-to-prevent-leaking-tlb-entry +++ a/mm/oom_kill.c @@ -554,7 +554,6 @@ static bool __oom_reap_task_mm(struct ta */ set_bit(MMF_UNSTABLE, &mm->flags); - tlb_gather_mmu(&tlb, mm, 0, -1); for (vma = mm->mmap ; vma; vma = vma->vm_next) { if (!can_madv_dontneed_vma(vma)) continue; @@ -569,11 +568,13 @@ static bool __oom_reap_task_mm(struct ta * we do not want to block exit_mmap by keeping mm ref * count elevated without a good reason. */ - if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) + if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) { + tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end); unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end, NULL); + tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end); + } } - tlb_finish_mmu(&tlb, 0, -1); pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n", task_pid_nr(tsk), tsk->comm, K(get_mm_counter(mm, MM_ANONPAGES)), _ Patches currently in -mm which might be from wangnan0@xxxxxxxxxx are mm-oom_reaper-gather-each-vma-to-prevent-leaking-tlb-entry.patch