linux-kernel - [PATCH 3.16 151/178] zram: do not use copy

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Message-ID: <lsq.1500213406.610023323@decadent.org.uk>
Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Sergey Senozhatsky" <sergey.senozhatsky@...il.com>,
        "Minchan Kim" <minchan@...nel.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 151/178] zram: do not use copy_page with non-page
 aligned address

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Minchan Kim <minchan@...nel.org>

commit d72e9a7a93e4f8e9e52491921d99e0c8aa89eb4e upstream.

The copy_page is optimized memcpy for page-alinged address.  If it is
used with non-page aligned address, it can corrupt memory which means
system corruption.  With zram, it can happen with

1. 64K architecture
2. partial IO
3. slub debug

Partial IO need to allocate a page and zram allocates it via kmalloc.
With slub debug, kmalloc(PAGE_SIZE) doesn't return page-size aligned
address.  And finally, copy_page(mem, cmem) corrupts memory.

So, this patch changes it to memcpy.

Actuaully, we don't need to change zram_bvec_write part because zsmalloc
returns page-aligned address in case of PAGE_SIZE class but it's not
good to rely on the internal of zsmalloc.

Note:
 When this patch is merged to stable, clear_page should be fixed, too.
 Unfortunately, recent zram removes it by "same page merge" feature so
 it's hard to backport this patch to -stable tree.

I will handle it when I receive the mail from stable tree maintainer to
merge this patch to backport.

Fixes: 42e99bd ("zram: optimize memory operations with clear_page()/copy_page()")
Link: http://lkml.kernel.org/r/1492042622-12074-2-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@...nel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16, replacing clear_page() as advised]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/block/zram/zram_drv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -345,13 +345,13 @@ static int zram_decompress_page(struct z

 	if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
 		read_unlock(&meta->tb_lock);
-		clear_page(mem);
+		memset(mem, 0, PAGE_SIZE);
 		return 0;
 	}

 	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE)
-		copy_page(mem, cmem);
+		memcpy(mem, cmem, PAGE_SIZE);
 	else
 		ret = zcomp_decompress(zram->comp, cmem, size, mem);
 	zs_unmap_object(meta->mem_pool, handle);
@@ -501,7 +501,7 @@ static int zram_bvec_write(struct zram *

 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
 		src = kmap_atomic(page);
-		copy_page(cmem, src);
+		memcpy(cmem, src, PAGE_SIZE);
 		kunmap_atomic(src);
 	} else {
 		memcpy(cmem, src, clen);