Re: [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
On Tue, Jul 2, 2019 at 11:03 PM Vitaly Wool wrote: > > On Tue, Jul 2, 2019 at 6:57 PM Henry Burns wrote: > > > > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool wrote: > > > > > > Hi Henry, > > > > > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns wrote: > > > > > > > > Running z3fold stress testing with address sanitization > > > > showed zhdr->slots was being used after it was freed. > > > > > > > > z3fold_free(z3fold_pool, handle) > > > > free_handle(handle) > > > > kmem_cache_free(pool->c_handle, zhdr->slots) > > > > release_z3fold_page_locked_list(kref) > > > > __release_z3fold_page(zhdr, true) > > > > zhdr_to_pool(zhdr) > > > > slots_to_pool(zhdr->slots) *BOOM* > > > > > > Thanks for looking into this. I'm not entirely sure I'm all for > > > splitting free_handle() but let me think about it. > > > > > > > Instead we split free_handle into two functions, release_handle() > > > > and free_slots(). We use release_handle() in place of free_handle(), > > > > and use free_slots() to call kmem_cache_free() after > > > > __release_z3fold_page() is done. > > > > > > A little less intrusive solution would be to move backlink to pool > > > from slots back to z3fold_header. Looks like it was a bad idea from > > > the start. > > > > > > Best regards, > > >Vitaly > > > > We still want z3fold pages to be movable though. Wouldn't moving > > the backink to the pool from slots to z3fold_header prevent us from > > enabling migration? > > That is a valid point but we can just add back pool pointer to > z3fold_header. The thing here is, there's another patch in the > pipeline that allows for a better (inter-page) compaction and it will > somewhat complicate things, because sometimes slots will have to be > released after z3fold page is released (because they will hold a > handle to another z3fold page). I would prefer that we just added back > pool to z3fold_header and changed zhdr_to_pool to just return > zhdr->pool, then had the compaction patch valid again, and then we > could come back to size optimization. > By adding pool pointer back to z3fold_header, will we still be able to move/migrate/compact the z3fold pages?
Re: [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
> > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool wrote: > > > > > > Hi Henry, > > > > > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns wrote: > > > > > > > > Running z3fold stress testing with address sanitization > > > > showed zhdr->slots was being used after it was freed. > > > > > > > > z3fold_free(z3fold_pool, handle) > > > > free_handle(handle) > > > > kmem_cache_free(pool->c_handle, zhdr->slots) > > > > release_z3fold_page_locked_list(kref) > > > > __release_z3fold_page(zhdr, true) > > > > zhdr_to_pool(zhdr) > > > > slots_to_pool(zhdr->slots) *BOOM* > > > > > > Thanks for looking into this. I'm not entirely sure I'm all for > > > splitting free_handle() but let me think about it. > > > > > > > Instead we split free_handle into two functions, release_handle() > > > > and free_slots(). We use release_handle() in place of free_handle(), > > > > and use free_slots() to call kmem_cache_free() after > > > > __release_z3fold_page() is done. > > > > > > A little less intrusive solution would be to move backlink to pool > > > from slots back to z3fold_header. Looks like it was a bad idea from > > > the start. > > > > > > Best regards, > > >Vitaly > > > > We still want z3fold pages to be movable though. Wouldn't moving > > the backink to the pool from slots to z3fold_header prevent us from > > enabling migration? > > That is a valid point but we can just add back pool pointer to > z3fold_header. The thing here is, there's another patch in the > pipeline that allows for a better (inter-page) compaction and it will > somewhat complicate things, because sometimes slots will have to be > released after z3fold page is released (because they will hold a > handle to another z3fold page). I would prefer that we just added back > pool to z3fold_header and changed zhdr_to_pool to just return > zhdr->pool, then had the compaction patch valid again, and then we > could come back to size optimization. I see your point, patch incoming.
Re: [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
On Tue, Jul 2, 2019 at 6:57 PM Henry Burns wrote: > > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool wrote: > > > > Hi Henry, > > > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns wrote: > > > > > > Running z3fold stress testing with address sanitization > > > showed zhdr->slots was being used after it was freed. > > > > > > z3fold_free(z3fold_pool, handle) > > > free_handle(handle) > > > kmem_cache_free(pool->c_handle, zhdr->slots) > > > release_z3fold_page_locked_list(kref) > > > __release_z3fold_page(zhdr, true) > > > zhdr_to_pool(zhdr) > > > slots_to_pool(zhdr->slots) *BOOM* > > > > Thanks for looking into this. I'm not entirely sure I'm all for > > splitting free_handle() but let me think about it. > > > > > Instead we split free_handle into two functions, release_handle() > > > and free_slots(). We use release_handle() in place of free_handle(), > > > and use free_slots() to call kmem_cache_free() after > > > __release_z3fold_page() is done. > > > > A little less intrusive solution would be to move backlink to pool > > from slots back to z3fold_header. Looks like it was a bad idea from > > the start. > > > > Best regards, > >Vitaly > > We still want z3fold pages to be movable though. Wouldn't moving > the backink to the pool from slots to z3fold_header prevent us from > enabling migration? That is a valid point but we can just add back pool pointer to z3fold_header. The thing here is, there's another patch in the pipeline that allows for a better (inter-page) compaction and it will somewhat complicate things, because sometimes slots will have to be released after z3fold page is released (because they will hold a handle to another z3fold page). I would prefer that we just added back pool to z3fold_header and changed zhdr_to_pool to just return zhdr->pool, then had the compaction patch valid again, and then we could come back to size optimization. Best regards, Vitaly
Re: [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool wrote: > > Hi Henry, > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns wrote: > > > > Running z3fold stress testing with address sanitization > > showed zhdr->slots was being used after it was freed. > > > > z3fold_free(z3fold_pool, handle) > > free_handle(handle) > > kmem_cache_free(pool->c_handle, zhdr->slots) > > release_z3fold_page_locked_list(kref) > > __release_z3fold_page(zhdr, true) > > zhdr_to_pool(zhdr) > > slots_to_pool(zhdr->slots) *BOOM* > > Thanks for looking into this. I'm not entirely sure I'm all for > splitting free_handle() but let me think about it. > > > Instead we split free_handle into two functions, release_handle() > > and free_slots(). We use release_handle() in place of free_handle(), > > and use free_slots() to call kmem_cache_free() after > > __release_z3fold_page() is done. > > A little less intrusive solution would be to move backlink to pool > from slots back to z3fold_header. Looks like it was a bad idea from > the start. > > Best regards, >Vitaly We still want z3fold pages to be movable though. Wouldn't moving the backink to the pool from slots to z3fold_header prevent us from enabling migration?
Re: [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
Hi Henry, On Mon, Jul 1, 2019 at 8:31 PM Henry Burns wrote: > > Running z3fold stress testing with address sanitization > showed zhdr->slots was being used after it was freed. > > z3fold_free(z3fold_pool, handle) > free_handle(handle) > kmem_cache_free(pool->c_handle, zhdr->slots) > release_z3fold_page_locked_list(kref) > __release_z3fold_page(zhdr, true) > zhdr_to_pool(zhdr) > slots_to_pool(zhdr->slots) *BOOM* Thanks for looking into this. I'm not entirely sure I'm all for splitting free_handle() but let me think about it. > Instead we split free_handle into two functions, release_handle() > and free_slots(). We use release_handle() in place of free_handle(), > and use free_slots() to call kmem_cache_free() after > __release_z3fold_page() is done. A little less intrusive solution would be to move backlink to pool from slots back to z3fold_header. Looks like it was a bad idea from the start. Best regards, Vitaly
[PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
Running z3fold stress testing with address sanitization
showed zhdr->slots was being used after it was freed.
z3fold_free(z3fold_pool, handle)
free_handle(handle)
kmem_cache_free(pool->c_handle, zhdr->slots)
release_z3fold_page_locked_list(kref)
__release_z3fold_page(zhdr, true)
zhdr_to_pool(zhdr)
slots_to_pool(zhdr->slots) *BOOM*
Instead we split free_handle into two functions, release_handle()
and free_slots(). We use release_handle() in place of free_handle(),
and use free_slots() to call kmem_cache_free() after
__release_z3fold_page() is done.
Fixes: 7c2b8baa61fe ("mm/z3fold.c: add structure for buddy handles")
Signed-off-by: Henry Burns
---
mm/z3fold.c | 33 ++---
1 file changed, 14 insertions(+), 19 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index f7993ff778df..e174d1549734 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -213,31 +213,24 @@ static inline struct z3fold_buddy_slots
*handle_to_slots(unsigned long handle)
return (struct z3fold_buddy_slots *)(handle & ~(SLOTS_ALIGN - 1));
}
-static inline void free_handle(unsigned long handle)
+static inline void release_handle(unsigned long handle)
{
- struct z3fold_buddy_slots *slots;
- int i;
- bool is_free;
-
if (handle & (1 << PAGE_HEADLESS))
return;
WARN_ON(*(unsigned long *)handle == 0);
*(unsigned long *)handle = 0;
- slots = handle_to_slots(handle);
- is_free = true;
- for (i = 0; i <= BUDDY_MASK; i++) {
- if (slots->slot[i]) {
- is_free = false;
- break;
- }
- }
+}
- if (is_free) {
- struct z3fold_pool *pool = slots_to_pool(slots);
+/* At this point all of the slots should be empty */
+static inline void free_slots(struct z3fold_buddy_slots *slots)
+{
+ struct z3fold_pool *pool = slots_to_pool(slots);
+ int i;
- kmem_cache_free(pool->c_handle, slots);
- }
+ for (i = 0; i <= BUDDY_MASK; i++)
+ VM_BUG_ON(slots->slot[i]);
+ kmem_cache_free(pool->c_handle, slots);
}
static struct dentry *z3fold_do_mount(struct file_system_type *fs_type,
@@ -431,7 +424,8 @@ static inline struct z3fold_pool *zhdr_to_pool(struct
z3fold_header *zhdr)
static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
{
struct page *page = virt_to_page(zhdr);
- struct z3fold_pool *pool = zhdr_to_pool(zhdr);
+ struct z3fold_buddy_slots *slots = zhdr->slots;
+ struct z3fold_pool *pool = slots_to_pool(slots);
WARN_ON(!list_empty(>buddy));
set_bit(PAGE_STALE, >private);
@@ -442,6 +436,7 @@ static void __release_z3fold_page(struct z3fold_header
*zhdr, bool locked)
spin_unlock(>lock);
if (locked)
z3fold_page_unlock(zhdr);
+ free_slots(slots);
spin_lock(>stale_lock);
list_add(>buddy, >stale);
queue_work(pool->release_wq, >work);
@@ -1009,7 +1004,7 @@ static void z3fold_free(struct z3fold_pool *pool,
unsigned long handle)
return;
}
- free_handle(handle);
+ release_handle(handle);
if (kref_put(>refcount, release_z3fold_page_locked_list)) {
atomic64_dec(>pages_nr);
return;
--
2.22.0.410.gd8fdbe21b5-goog
