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Commit 5224c40e authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Greg Kroah-Hartman
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mm, gup: add missing refcount overflow checks on x86 and s390 



The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from
overflowing page refcount") was backported to 4.9.y stable as commit
2ed768cf. The backport however missed that in 4.9, there are several
arch-specific gup.c versions with fast gup implementations, so these do not
prevent refcount overflow.

This is partially fixed for x86 in stable-only commit d73af797 ("x86, mm,
gup: prevent get_page() race with munmap in paravirt guest"). This stable-only
commit adds missing parts to x86 version, as well as s390 version, both taken
from the SUSE SLES/openSUSE 4.12-based kernels.

The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely
the known overflow scenario based on FUSE, which needs 140GB of RAM, is a
problem for those architectures, and I don't feel confident enough to patch
them.

Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fb87c6c5

arch/s390/mm/gup.c

+6 −3
Original line number Diff line number Diff line
@@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

		page = pte_page(pte);

		head = compound_head(page);

		if (!page_cache_get_speculative(head))

		if (WARN_ON_ONCE(page_ref_count(head) < 0)

		    || !page_cache_get_speculative(head))

			return 0;

		if (unlikely(pte_val(pte) != pte_val(*ptep))) {

			put_page(head);
@@ -76,7 +77,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
		refs++;

	} while (addr += PAGE_SIZE, addr != end);



	if (!page_cache_add_speculative(head, refs)) {

	if (WARN_ON_ONCE(page_ref_count(head) < 0)

	    || !page_cache_add_speculative(head, refs)) {

		*nr -= refs;

		return 0;

	}
@@ -150,7 +152,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr, 
		refs++;

	} while (addr += PAGE_SIZE, addr != end);



	if (!page_cache_add_speculative(head, refs)) {

	if (WARN_ON_ONCE(page_ref_count(head) < 0)

	    || !page_cache_add_speculative(head, refs)) {

		*nr -= refs;

		return 0;

	}

arch/x86/mm/gup.c

+8 −1
Original line number Diff line number Diff line
@@ -202,9 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, 
			undo_dev_pagemap(nr, nr_start, pages);

			return 0;

		}

		if (unlikely(!try_get_page(page))) {

			put_dev_pagemap(pgmap);

			return 0;

		}

		SetPageReferenced(page);

		pages[*nr] = page;

		get_page(page);

		put_dev_pagemap(pgmap);

		(*nr)++;

		pfn++;
@@ -230,6 +233,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, 


	refs = 0;

	head = pmd_page(pmd);

	if (WARN_ON_ONCE(page_ref_count(head) <= 0))

		return 0;

	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);

	do {

		VM_BUG_ON_PAGE(compound_head(page) != head, page);
@@ -289,6 +294,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, 


	refs = 0;

	head = pud_page(pud);

	if (WARN_ON_ONCE(page_ref_count(head) <= 0))

		return 0;

	page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);

	do {

		VM_BUG_ON_PAGE(compound_head(page) != head, page);