Commit 8fcef5e0 authored Sep 11, 2016 by Lorenzo Stoakes Committed by Greg Kroah-Hartman Oct 17, 2021

mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing

commit 38e088546522e1e86d2b8f401a1354ad3a9b3303 upstream.

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 c0e7cad9 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>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
[cascardo: context adjustments were necessary]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 58facc9c

mm/huge_memory.c

+0 −3

Original line number	Diff line number	Diff line
		@@ -1340,9 +1340,6 @@ int do_huge_pmd_numa_page(struct mm_struct mm, struct vm_area_struct vma,
		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)));

		ptl = pmd_lock(mm, pmdp);
		if (unlikely(!pmd_same(pmd, *pmdp)))
		goto out_unlock;

mm/memory.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -3209,9 +3209,6 @@ static int do_numa_page(struct mm_struct mm, struct vm_area_struct vma,
		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
		@@ -3304,6 +3301,11 @@ static int wp_huge_pmd(struct mm_struct mm, struct vm_area_struct vma,
		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
		@@ -3350,7 +3352,7 @@ static int handle_pte_fault(struct mm_struct *mm,
		pte, pmd, flags, entry);
		}

		if (pte_protnone(entry))
		if (pte_protnone(entry) && vma_is_accessible(vma))
		return do_numa_page(mm, vma, address, entry, pte, pmd);

		ptl = pte_lockptr(mm, pmd);
		@@ -3425,7 +3427,7 @@ static int __handle_mm_fault(struct mm_struct mm, struct vm_area_struct vma,
		if (pmd_trans_splitting(orig_pmd))
		return 0;

		if (pmd_protnone(orig_pmd))
		if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
		return do_huge_pmd_numa_page(mm, vma, address,
		orig_pmd, pmd);