The patch titled
Subject: zsmalloc: calling zs_map_object() from irq is a bug
has been added to the -mm tree. Its filename is
zsmalloc-calling-zs_map_object-from-irq-is-a-bug.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zsmalloc-calling-zs_map_object-from-irq-is-a-bug.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zsmalloc-calling-zs_map_object-from-irq-is-a-bug.patch
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------------------------------------------------------
From: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Subject: 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@xxxxxxxxx
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/zsmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/zsmalloc.c~zsmalloc-calling-zs_map_object-from-irq-is-a-bug mm/zsmalloc.c
--- a/mm/zsmalloc.c~zsmalloc-calling-zs_map_object-from-irq-is-a-bug
+++ a/mm/zsmalloc.c
@@ -1349,7 +1349,7 @@ 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);
_
Patches currently in -mm which might be from sergey.senozhatsky.work@xxxxxxxxx are
ratelimit-use-deferred-printk-version.patch
zram-add-zstd-to-the-supported-algorithms-list.patch
zram-remove-zlib-from-the-list-of-recommended-algorithms.patch
zsmalloc-calling-zs_map_object-from-irq-is-a-bug.patch
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