diff options
| author | Lorenzo Stoakes <lstoakes@gmail.com> | 2016-09-11 23:54:25 +0100 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-09-25 15:43:42 -0700 |
| commit | 38e088546522e1e86d2b8f401a1354ad3a9b3303 (patch) | |
| tree | 3e7144eb3ecd99edd02d0c2bb44e962d1982fd42 /mm/memory.c | |
| parent | 831e45d84a971495c882bc186d98bbb825b2ee59 (diff) | |
mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing
The NUMA balancing logic uses an arch-specific PROT_NONE page table flag
defined by pte_protnone() or pmd_protnone() to mark PTEs or huge page
PMDs respectively as requiring balancing upon a subsequent page fault.
User-defined PROT_NONE memory regions which also have this flag set will
not normally invoke the NUMA balancing code as do_page_fault() will send
a segfault to the process before handle_mm_fault() is even called.
However if access_remote_vm() is invoked to access a PROT_NONE region of
memory, handle_mm_fault() is called via faultin_page() and
__get_user_pages() without any access checks being performed, meaning
the NUMA balancing logic is incorrectly invoked on a non-NUMA memory
region.
A simple means of triggering this problem is to access PROT_NONE mmap'd
memory using /proc/self/mem which reliably results in the NUMA handling
functions being invoked when CONFIG_NUMA_BALANCING is set.
This issue was reported in bugzilla (issue 99101) which includes some
simple repro code.
There are BUG_ON() checks in do_numa_page() and do_huge_pmd_numa_page()
added at commit c0e7cad to avoid accidentally provoking strange
behaviour by attempting to apply NUMA balancing to pages that are in
fact PROT_NONE. The BUG_ON()'s are consistently triggered by the repro.
This patch moves the PROT_NONE check into mm/memory.c rather than
invoking BUG_ON() as faulting in these pages via faultin_page() is a
valid reason for reaching the NUMA check with the PROT_NONE page table
flag set and is therefore not always a bug.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=99101
Reported-by: Trevor Saunders <tbsaunde@tbsaunde.org>
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
| -rw-r--r-- | mm/memory.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/mm/memory.c b/mm/memory.c index 83be99d9d8a1..793fe0f9841c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3351,9 +3351,6 @@ static int do_numa_page(struct fault_env *fe, pte_t pte) bool was_writable = pte_write(pte); int flags = 0; - /* A PROT_NONE fault should not end up here */ - BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))); - /* * The "pte" at this point cannot be used safely without * validation through pte_unmap_same(). It's of NUMA type but @@ -3458,6 +3455,11 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd) return VM_FAULT_FALLBACK; } +static inline bool vma_is_accessible(struct vm_area_struct *vma) +{ + return vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE); +} + /* * These routines also need to handle stuff like marking pages dirty * and/or accessed for architectures that don't do it in hardware (most @@ -3524,7 +3526,7 @@ static int handle_pte_fault(struct fault_env *fe) if (!pte_present(entry)) return do_swap_page(fe, entry); - if (pte_protnone(entry)) + if (pte_protnone(entry) && vma_is_accessible(fe->vma)) return do_numa_page(fe, entry); fe->ptl = pte_lockptr(fe->vma->vm_mm, fe->pmd); @@ -3590,7 +3592,7 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address, barrier(); if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) { - if (pmd_protnone(orig_pmd)) + if (pmd_protnone(orig_pmd) && vma_is_accessible(vma)) return do_huge_pmd_numa_page(&fe, orig_pmd); if ((fe.flags & FAULT_FLAG_WRITE) && |