+ zsmalloc-zero-initialize-zspage-memory-to-prevent-kmsan-uninit-reads.patch added to mm-hotfixes-unstable branch

+ zsmalloc-zero-initialize-zspage-memory-to-prevent-kmsan-uninit-reads.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: zsmalloc: zero-initialize zspage memory to prevent KMSAN uninit reads
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     zsmalloc-zero-initialize-zspage-memory-to-prevent-kmsan-uninit-reads.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zsmalloc-zero-initialize-zspage-memory-to-prevent-kmsan-uninit-reads.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Kartik Nair <contact.kartikn@gmail.com>
Subject: zsmalloc: zero-initialize zspage memory to prevent KMSAN uninit reads
Date: Tue, 12 May 2026 03:06:58 +0530

Pages allocated via alloc_zpdesc() use alloc_pages_node() without
__GFP_ZERO, leaving physical memory uninitialized.  When a compressed
object spans two physical pages in a zspage, zs_obj_read_sg_begin() sets
up a scatterlist pointing directly at the raw second page.  If the second
page was freshly allocated and never written beyond the object boundary,
KMSAN detects reads of uninitialized memory downstream in the decompressor
(e.g.  sw842_decompress reading the CRC trailer).

Fix this by passing __GFP_ZERO to alloc_zpdesc() in alloc_zspage() so
all pages backing a zspage are zero-initialized at allocation time.

Link: https://lore.kernel.org/20260511213658.25273-1-contact.kartikn@gmail.com
Fixes: 56e5a103a721 ("zsmalloc: prefer the the original page's node for compressed data")
Reported-by: syzbot+8f77ff6144a73f0cf71b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8f77ff6144a73f0cf71b
Signed-off-by: Kartik Nair <contact.kartikn@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zsmalloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/zsmalloc.c~zsmalloc-zero-initialize-zspage-memory-to-prevent-kmsan-uninit-reads
+++ a/mm/zsmalloc.c
@@ -951,7 +951,7 @@ static struct zspage *alloc_zspage(struc
 	for (i = 0; i < class->pages_per_zspage; i++) {
 		struct zpdesc *zpdesc;
 
-		zpdesc = alloc_zpdesc(gfp, nid);
+		zpdesc = alloc_zpdesc(gfp | __GFP_ZERO, nid);
 		if (!zpdesc) {
 			while (--i >= 0) {
 				zpdesc_dec_zone_page_state(zpdescs[i]);
_

Patches currently in -mm which might be from contact.kartikn@gmail.com are

zsmalloc-zero-initialize-zspage-memory-to-prevent-kmsan-uninit-reads.patch