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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>
This commit is contained in:
parent
831e45d84a
commit
38e0885465
@ -1138,9 +1138,6 @@ int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd)
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bool was_writable;
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int flags = 0;
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/* A PROT_NONE fault should not end up here */
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BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
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fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
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if (unlikely(!pmd_same(pmd, *fe->pmd)))
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goto out_unlock;
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12
mm/memory.c
12
mm/memory.c
@ -3351,9 +3351,6 @@ static int do_numa_page(struct fault_env *fe, pte_t pte)
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bool was_writable = pte_write(pte);
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int flags = 0;
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/* A PROT_NONE fault should not end up here */
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BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
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/*
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* The "pte" at this point cannot be used safely without
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* validation through pte_unmap_same(). It's of NUMA type but
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@ -3458,6 +3455,11 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd)
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return VM_FAULT_FALLBACK;
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}
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static inline bool vma_is_accessible(struct vm_area_struct *vma)
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{
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return vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE);
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}
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/*
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* These routines also need to handle stuff like marking pages dirty
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* and/or accessed for architectures that don't do it in hardware (most
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@ -3524,7 +3526,7 @@ static int handle_pte_fault(struct fault_env *fe)
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if (!pte_present(entry))
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return do_swap_page(fe, entry);
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if (pte_protnone(entry))
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if (pte_protnone(entry) && vma_is_accessible(fe->vma))
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return do_numa_page(fe, entry);
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fe->ptl = pte_lockptr(fe->vma->vm_mm, fe->pmd);
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@ -3590,7 +3592,7 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
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barrier();
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if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
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if (pmd_protnone(orig_pmd))
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if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
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return do_huge_pmd_numa_page(&fe, orig_pmd);
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if ((fe.flags & FAULT_FLAG_WRITE) &&
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