path: root/mm
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authorLorenzo Stoakes <lstoakes@gmail.com>2016-09-11 23:54:25 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2016-09-25 15:43:42 -0700
commit38e088546522e1e86d2b8f401a1354ad3a9b3303 (patch)
tree3e7144eb3ecd99edd02d0c2bb44e962d1982fd42 /mm
parent831e45d84a971495c882bc186d98bbb825b2ee59 (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')
2 files changed, 7 insertions, 8 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a6abd76baa72..53ae6d00656a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1138,9 +1138,6 @@ int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd)
bool was_writable;
int flags = 0;
- /* A PROT_NONE fault should not end up here */
- BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
if (unlikely(!pmd_same(pmd, *fe->pmd)))
goto out_unlock;
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)
+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,
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) &&