On Fri, 2019-11-29 at 10:03 +0100, Vlastimil Babka wrote:

The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.9.y stable as commit 2ed768cfd895. 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 d73af79742e7 ("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: Vlastimil Babka vbabka@suse.cz

arch/s390/mm/gup.c | 9 ++++++--- arch/x86/mm/gup.c | 10 ++++++++-- 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 97fc449a7470..33a940389a6d 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -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 (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0)
  

No need for unlikely(); WARN_ON() includes that.

•     || !page_cache_get_speculative(head)))
  return 0;
  

  if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head);

[...]

--- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -202,10 +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);
  

This leaks a pgmap reference on success!

(*nr)++;
pfn++;

} while (addr += PAGE_SIZE, addr != end); @@ -230,6 +232,8 @@ 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))

Why <= 0, given we use < 0 elsewhere?

• return 0;
  

  page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page);

@@ -289,6 +293,8 @@ 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))

Same question here.

Ben.

• return 0;
  

  page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page);

On Tue, Dec 03, 2019 at 01:50:26PM +0100, Vlastimil Babka wrote:

On 12/1/19 5:55 PM, Sasha Levin wrote:

...

On Fri, Nov 29, 2019 at 10:03:48AM +0100, Vlastimil Babka wrote:

...

This collection of patches add the missing overflow checks in arch-specific gup.c variants for x86 and s390. Those were missed in backport of 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") as mainline had a single gup.c implementation at that point. See individual patches for details.

Queued up, thanks!

Please replace the 4.9 version with the following fixed one, thanks to Ben:

----8<----

...

From fe7f18bd152094f8516d79e847fcb5453a6f8368 Mon Sep 17 00:00:00 2001

From: Vlastimil Babka vbabka@suse.cz Date: Wed, 6 Nov 2019 16:32:57 +0100 Subject: [PATCH] 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 2ed768cfd895. 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 d73af79742e7 ("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: Vlastimil Babka vbabka@suse.cz

arch/s390/mm/gup.c | 9 ++++++--- arch/x86/mm/gup.c | 9 ++++++++- 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 97fc449a7470..cf045f56581e 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -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; }

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index d7db45bdfb3b..82f727fbbbd2 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -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);

-- 2.24.0

Now updated, sorry I missed this earlier.

greg k-h