4.9-stable review patch. If anyone has any objections, please let me know.
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From: Sergey Senozhatsky sergey.senozhatsky.work@gmail.com
[ Upstream commit 1aedcafbf32b3f232c159b14cd0d423fcfe2b861 ]
Use BUG_ON(in_interrupt()) in zs_map_object(). This is not a new BUG_ON(), it's always been there, but was recently changed to VM_BUG_ON(). There are several problems there. First, we use use per-CPU mappings both in zsmalloc and in zram, and interrupt may easily corrupt those buffers. Second, and more importantly, we believe it's possible to start leaking sensitive information. Consider the following case:
-> process P swap out zram per-cpu mapping CPU1 compress page A -> IRQ
swap out zram per-cpu mapping CPU1 compress page B write page from per-cpu mapping CPU1 to zsmalloc pool iret
-> process P write page from per-cpu mapping CPU1 to zsmalloc pool [*] return
* so we store overwritten data that actually belongs to another page (task) and potentially contains sensitive data. And when process P will page fault it's going to read (swap in) that other task's data.
Link: http://lkml.kernel.org/r/20170929045140.4055-1-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky sergey.senozhatsky@gmail.com Acked-by: Minchan Kim minchan@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/zsmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1407,7 +1407,7 @@ void *zs_map_object(struct zs_pool *pool * pools/users, we can't allow mapping in interrupt context * because it can corrupt another users mappings. */ - WARN_ON_ONCE(in_interrupt()); + BUG_ON(in_interrupt());
/* From now on, migration cannot move the object */ pin_tag(handle);