[Linux-stable-mirror] [PATCHv2] mm, page_vma_mapped: Drop faulty pointer arithmetics in check_pte()
Tetsuo reported random crashes under memory pressure on 32-bit x86 system and tracked down to change that introduced page_vma_mapped_walk().
The root cause of the issue is the faulty pointer math in check_pte(). As ->pte may point to an arbitrary page we have to check that they are belong to the section before doing math. Otherwise it may lead to weird results.
It wasn't noticed until now as mem_map[] is virtually contiguous on flatmem or vmemmap sparsemem. Pointer arithmetic just works against all 'struct page' pointers. But with classic sparsemem, it doesn't because each section memap is allocated separately and so consecutive pfns crossing two sections might have struct pages at completely unrelated addresses.
Let's restructure code a bit and replace pointer arithmetic with operations on pfns.
Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reported-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()") Cc: stable@vger.kernel.org --- v2: - Do not use uninitialized 'pfn' for !MIGRATION case (Michal)
--- include/linux/swapops.h | 21 +++++++++++++++++ mm/page_vma_mapped.c | 63 +++++++++++++++++++++++++++++-------------------- 2 files changed, 59 insertions(+), 25 deletions(-)
diff --git a/include/linux/swapops.h b/include/linux/swapops.h index 9c5a2628d6ce..1d3877c39a00 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -124,6 +124,11 @@ static inline bool is_write_device_private_entry(swp_entry_t entry) return unlikely(swp_type(entry) == SWP_DEVICE_WRITE); }
+static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry) +{ + return swp_offset(entry); +} + static inline struct page *device_private_entry_to_page(swp_entry_t entry) { return pfn_to_page(swp_offset(entry)); @@ -154,6 +159,11 @@ static inline bool is_write_device_private_entry(swp_entry_t entry) return false; }
+static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry) +{ + return 0; +} + static inline struct page *device_private_entry_to_page(swp_entry_t entry) { return NULL; @@ -189,6 +199,11 @@ static inline int is_write_migration_entry(swp_entry_t entry) return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE); }
+static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) +{ + return swp_offset(entry); +} + static inline struct page *migration_entry_to_page(swp_entry_t entry) { struct page *p = pfn_to_page(swp_offset(entry)); @@ -218,6 +233,12 @@ static inline int is_migration_entry(swp_entry_t swp) { return 0; } + +static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) +{ + return 0; +} + static inline struct page *migration_entry_to_page(swp_entry_t entry) { return NULL; diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index d22b84310f6d..956015614395 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -30,10 +30,29 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) return true; }
+/** + * check_pte - check if @pvmw->page is mapped at the @pvmw->pte + * + * page_vma_mapped_walk() found a place where @pvmw->page is *potentially* + * mapped. check_pte() has to validate this. + * + * @pvmw->pte may point to empty PTE, swap PTE or PTE pointing to arbitrary + * page. + * + * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration + * entry that points to @pvmw->page or any subpage in case of THP. + * + * If PVMW_MIGRATION flag is not set, returns true if @pvmw->pte points to + * @pvmw->page or any subpage in case of THP. + * + * Otherwise, return false. + * + */ static bool check_pte(struct page_vma_mapped_walk *pvmw) { + unsigned long pfn; + if (pvmw->flags & PVMW_MIGRATION) { -#ifdef CONFIG_MIGRATION swp_entry_t entry; if (!is_swap_pte(*pvmw->pte)) return false; @@ -41,37 +60,31 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
if (!is_migration_entry(entry)) return false; - if (migration_entry_to_page(entry) - pvmw->page >= - hpage_nr_pages(pvmw->page)) { - return false; - } - if (migration_entry_to_page(entry) < pvmw->page) - return false; -#else - WARN_ON_ONCE(1); -#endif - } else { - if (is_swap_pte(*pvmw->pte)) { - swp_entry_t entry;
- entry = pte_to_swp_entry(*pvmw->pte); - if (is_device_private_entry(entry) && - device_private_entry_to_page(entry) == pvmw->page) - return true; - } + pfn = migration_entry_to_pfn(entry); + } else if (is_swap_pte(*pvmw->pte)) { + swp_entry_t entry;
- if (!pte_present(*pvmw->pte)) + /* Handle un-addressable ZONE_DEVICE memory */ + entry = pte_to_swp_entry(*pvmw->pte); + if (!is_device_private_entry(entry)) return false;
- /* THP can be referenced by any subpage */ - if (pte_page(*pvmw->pte) - pvmw->page >= - hpage_nr_pages(pvmw->page)) { - return false; - } - if (pte_page(*pvmw->pte) < pvmw->page) + pfn = device_private_entry_to_pfn(entry); + } else { + if (!pte_present(*pvmw->pte)) return false; + + pfn = pte_pfn(*pvmw->pte); }
+ if (pfn < page_to_pfn(pvmw->page)) + return false; + + /* THP can be referenced by any subpage */ + if (pfn - page_to_pfn(pvmw->page) >= hpage_nr_pages(pvmw->page)) + return false; + return true; }
On Fri 19-01-18 15:49:24, Kirill A. Shutemov wrote:
Tetsuo reported random crashes under memory pressure on 32-bit x86 system and tracked down to change that introduced page_vma_mapped_walk().
The root cause of the issue is the faulty pointer math in check_pte(). As ->pte may point to an arbitrary page we have to check that they are belong to the section before doing math. Otherwise it may lead to weird results.
It wasn't noticed until now as mem_map[] is virtually contiguous on flatmem or vmemmap sparsemem. Pointer arithmetic just works against all 'struct page' pointers. But with classic sparsemem, it doesn't because each section memap is allocated separately and so consecutive pfns crossing two sections might have struct pages at completely unrelated addresses.
Let's restructure code a bit and replace pointer arithmetic with operations on pfns.
Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reported-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()") Cc: stable@vger.kernel.org
Much better. Thanks! Acked-by: Michal Hocko mhocko@suse.com
v2:
- Do not use uninitialized 'pfn' for !MIGRATION case (Michal)
include/linux/swapops.h | 21 +++++++++++++++++ mm/page_vma_mapped.c | 63 +++++++++++++++++++++++++++++-------------------- 2 files changed, 59 insertions(+), 25 deletions(-)
diff --git a/include/linux/swapops.h b/include/linux/swapops.h index 9c5a2628d6ce..1d3877c39a00 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -124,6 +124,11 @@ static inline bool is_write_device_private_entry(swp_entry_t entry) return unlikely(swp_type(entry) == SWP_DEVICE_WRITE); } +static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry) +{
- return swp_offset(entry);
+}
static inline struct page *device_private_entry_to_page(swp_entry_t entry) { return pfn_to_page(swp_offset(entry)); @@ -154,6 +159,11 @@ static inline bool is_write_device_private_entry(swp_entry_t entry) return false; } +static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry) +{
- return 0;
+}
static inline struct page *device_private_entry_to_page(swp_entry_t entry) { return NULL; @@ -189,6 +199,11 @@ static inline int is_write_migration_entry(swp_entry_t entry) return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE); } +static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) +{
- return swp_offset(entry);
+}
static inline struct page *migration_entry_to_page(swp_entry_t entry) { struct page *p = pfn_to_page(swp_offset(entry)); @@ -218,6 +233,12 @@ static inline int is_migration_entry(swp_entry_t swp) { return 0; }
+static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) +{
- return 0;
+}
static inline struct page *migration_entry_to_page(swp_entry_t entry) { return NULL; diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index d22b84310f6d..956015614395 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -30,10 +30,29 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) return true; } +/**
- check_pte - check if @pvmw->page is mapped at the @pvmw->pte
- page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
- mapped. check_pte() has to validate this.
- @pvmw->pte may point to empty PTE, swap PTE or PTE pointing to arbitrary
- page.
- If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
- entry that points to @pvmw->page or any subpage in case of THP.
- If PVMW_MIGRATION flag is not set, returns true if @pvmw->pte points to
- @pvmw->page or any subpage in case of THP.
- Otherwise, return false.
- */
static bool check_pte(struct page_vma_mapped_walk *pvmw) {
- unsigned long pfn;
- if (pvmw->flags & PVMW_MIGRATION) {
-#ifdef CONFIG_MIGRATION swp_entry_t entry; if (!is_swap_pte(*pvmw->pte)) return false; @@ -41,37 +60,31 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw) if (!is_migration_entry(entry)) return false;
if (migration_entry_to_page(entry) - pvmw->page >=hpage_nr_pages(pvmw->page)) {return false;}if (migration_entry_to_page(entry) < pvmw->page)return false;-#else
WARN_ON_ONCE(1);-#endif
- } else {
if (is_swap_pte(*pvmw->pte)) {swp_entry_t entry;
entry = pte_to_swp_entry(*pvmw->pte);if (is_device_private_entry(entry) &&device_private_entry_to_page(entry) == pvmw->page)return true;}
pfn = migration_entry_to_pfn(entry);- } else if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
if (!pte_present(*pvmw->pte))
/* Handle un-addressable ZONE_DEVICE memory */entry = pte_to_swp_entry(*pvmw->pte);if (!is_device_private_entry(entry)) return false;
/* THP can be referenced by any subpage */if (pte_page(*pvmw->pte) - pvmw->page >=hpage_nr_pages(pvmw->page)) {return false;}if (pte_page(*pvmw->pte) < pvmw->page)
pfn = device_private_entry_to_pfn(entry);- } else {
if (!pte_present(*pvmw->pte)) return false;pfn = pte_pfn(*pvmw->pte);
- if (pfn < page_to_pfn(pvmw->page))
return false;- /* THP can be referenced by any subpage */
- if (pfn - page_to_pfn(pvmw->page) >= hpage_nr_pages(pvmw->page))
return false;- return true;
} -- 2.15.1
On Fri, Jan 19, 2018 at 4:49 AM, Kirill A. Shutemov kirill.shutemov@linux.intel.com wrote:
if (pfn < page_to_pfn(pvmw->page))return false;/* THP can be referenced by any subpage */if (pfn - page_to_pfn(pvmw->page) >= hpage_nr_pages(pvmw->page))return false;
Is gcc actually clever enough to merge these? The "page_to_pfn()" logic can be pretty expensive (exactly for the sparsemem case, but per-node DISCOTIGMEM has some complexity too.
So I'd prefer to make that explicit, perhaps by having a helper function that does this something like
static inline bool pfn_in_hpage(unsigned long pfn, struct page *hpage) { unsigned long hpage_pfn = page_to_pfn(hpage);
return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage); }
and then just use
return pfn_in_hpage(pfn, pvmw->page);
in that caller. Hmm? Wouldn't that be more legible, and avoid the repeated pvmw->page and page_to_pfn() cases?
Even if maybe gcc can do the CSE and turn it all into the same thing in the end..
Linus
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Kirill A. Shutemov -
Linus Torvalds -
Michal Hocko