ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 51 insertions, 0 deletions

diff --git a/fs/jffs2/writev.c b/fs/jffs2/writev.c
new file mode 100644
index 000000000..a1bda9dab
--- /dev/null
+++ b/fs/jffs2/writev.c
@@ -0,0 +1,51 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ *
+ * Created by David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/mtd/mtd.h>
+#include "nodelist.h"
+
+int jffs2_flash_direct_writev(struct jffs2_sb_info *c, const struct kvec *vecs,
+			      unsigned long count, loff_t to, size_t *retlen)
+{
+	if (!jffs2_is_writebuffered(c)) {
+		if (jffs2_sum_active()) {
+			int res;
+			res = jffs2_sum_add_kvec(c, vecs, count, (uint32_t) to);
+			if (res) {
+				return res;
+			}
+		}
+	}
+
+	return mtd_writev(c->mtd, vecs, count, to, retlen);
+}
+
+int jffs2_flash_direct_write(struct jffs2_sb_info *c, loff_t ofs, size_t len,
+			size_t *retlen, const u_char *buf)
+{
+	int ret;
+	ret = mtd_write(c->mtd, ofs, len, retlen, buf);
+
+	if (jffs2_sum_active()) {
+		struct kvec vecs[1];
+		int res;
+
+		vecs[0].iov_base = (unsigned char *) buf;
+		vecs[0].iov_len = len;
+
+		res = jffs2_sum_add_kvec(c, vecs, 1, (uint32_t) ofs);
+		if (res) {
+			return res;
+		}
+	}
+	return ret;
+}