linux-kernel - [PATCH 2/3] mm/pagemap: Fix wr-protect even if PM_SCAN_WP

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Message-ID: <20231116201547.536857-3-peterx@redhat.com>
Date:   Thu, 16 Nov 2023 15:15:46 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     peterx@...hat.com,
        Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Andrei Vagin <avagin@...il.com>,
        syzbot+7ca4b2719dc742b8d0a4@...kaller.appspotmail.com
Subject: [PATCH 2/3] mm/pagemap: Fix wr-protect even if PM_SCAN_WP_MATCHING not set

The new pagemap ioctl contains a fast path for wr-protections without
looking into category masks.  It forgets to check PM_SCAN_WP_MATCHING
before applying the wr-protections.  It can cause, e.g., pte markers
installed on archs that do not even support uffd wr-protect.

WARNING: CPU: 0 PID: 5059 at mm/memory.c:1520 zap_pte_range mm/memory.c:1520 [inline]

Fixes: 12f6b01a0bcb ("fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag")
Reported-by: syzbot+7ca4b2719dc742b8d0a4@...kaller.appspotmail.com
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 fs/proc/task_mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e91085d79926..d19924bf0a39 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2171,7 +2171,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
 		return 0;
 	}
 
-	if (!p->vec_out) {
+	if ((p->arg.flags & PM_SCAN_WP_MATCHING) && !p->vec_out) {
 		/* Fast path for performing exclusive WP */
 		for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
 			if (pte_uffd_wp(ptep_get(pte)))
-- 
2.41.0