From 3595f96dc89e3202c9dc1b646bff35bdb4e4eef2 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Wed, 4 Oct 2017 01:04:23 +0000 Subject: [PATCH] zsmalloc: calling zs_map_object() from irq is a bug 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 Acked-by: Minchan Kim Signed-off-by: Andrew Morton --- mm/zsmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 7c38e850a8fc5c..685049a9048d8e 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1349,7 +1349,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle, * 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);