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SubjectRe: [PATCH v3] mm/memory.c: do_fault: avoid usage of stale vm_area_struct
On Sun, Mar 03, 2019 at 08:28:04AM +0100, Jan Stancek wrote:
> LTP testcase mtest06 [1] can trigger a crash on s390x running 5.0.0-rc8.
> This is a stress test, where one thread mmaps/writes/munmaps memory area
> and other thread is trying to read from it:
>
> CPU: 0 PID: 2611 Comm: mmap1 Not tainted 5.0.0-rc8+ #51
> Hardware name: IBM 2964 N63 400 (z/VM 6.4.0)
> Krnl PSW : 0404e00180000000 00000000001ac8d8 (__lock_acquire+0x7/0x7a8)
> Call Trace:
> ([<0000000000000000>] (null))
> [<00000000001adae4>] lock_acquire+0xec/0x258
> [<000000000080d1ac>] _raw_spin_lock_bh+0x5c/0x98
> [<000000000012a780>] page_table_free+0x48/0x1a8
> [<00000000002f6e54>] do_fault+0xdc/0x670
> [<00000000002fadae>] __handle_mm_fault+0x416/0x5f0
> [<00000000002fb138>] handle_mm_fault+0x1b0/0x320
> [<00000000001248cc>] do_dat_exception+0x19c/0x2c8
> [<000000000080e5ee>] pgm_check_handler+0x19e/0x200
>
> page_table_free() is called with NULL mm parameter, but because
> "0" is a valid address on s390 (see S390_lowcore), it keeps
> going until it eventually crashes in lockdep's lock_acquire.
> This crash is reproducible at least since 4.14.
>
> Problem is that "vmf->vma" used in do_fault() can become stale.
> Because mmap_sem may be released, other threads can come in,
> call munmap() and cause "vma" be returned to kmem cache, and
> get zeroed/re-initialized and re-used:
>
> handle_mm_fault |
> __handle_mm_fault |
> do_fault |
> vma = vmf->vma |
> do_read_fault |
> __do_fault |
> vma->vm_ops->fault(vmf); |
> mmap_sem is released |
> |
> | do_munmap()
> | remove_vma_list()
> | remove_vma()
> | vm_area_free()
> | # vma is released
> | ...
> | # same vma is allocated
> | # from kmem cache
> | do_mmap()
> | vm_area_alloc()
> | memset(vma, 0, ...)
> |
> pte_free(vma->vm_mm, ...); |
> page_table_free |
> spin_lock_bh(&mm->context.lock);|
> <crash> |
>
> Cache mm_struct to avoid using potentially stale "vma".
>
> [1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/mtest06/mmap1.c
>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

--
Kirill A. Shutemov

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