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, 91 insertions, 0 deletions

diff --git a/include/uapi/mtd/nftl-user.h b/include/uapi/mtd/nftl-user.h
new file mode 100644
index 000000000..b23bdc91c
--- /dev/null
+++ b/include/uapi/mtd/nftl-user.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#ifndef __MTD_NFTL_USER_H__
+#define __MTD_NFTL_USER_H__
+
+#include <linux/types.h>
+
+/* Block Control Information */
+
+struct nftl_bci {
+	unsigned char ECCSig[6];
+	__u8 Status;
+	__u8 Status1;
+}__attribute__((packed));
+
+/* Unit Control Information */
+
+struct nftl_uci0 {
+	__u16 VirtUnitNum;
+	__u16 ReplUnitNum;
+	__u16 SpareVirtUnitNum;
+	__u16 SpareReplUnitNum;
+} __attribute__((packed));
+
+struct nftl_uci1 {
+	__u32 WearInfo;
+	__u16 EraseMark;
+	__u16 EraseMark1;
+} __attribute__((packed));
+
+struct nftl_uci2 {
+        __u16 FoldMark;
+        __u16 FoldMark1;
+	__u32 unused;
+} __attribute__((packed));
+
+union nftl_uci {
+	struct nftl_uci0 a;
+	struct nftl_uci1 b;
+	struct nftl_uci2 c;
+};
+
+struct nftl_oob {
+	struct nftl_bci b;
+	union nftl_uci u;
+};
+
+/* NFTL Media Header */
+
+struct NFTLMediaHeader {
+	char DataOrgID[6];
+	__u16 NumEraseUnits;
+	__u16 FirstPhysicalEUN;
+	__u32 FormattedSize;
+	unsigned char UnitSizeFactor;
+} __attribute__((packed));
+
+#define MAX_ERASE_ZONES (8192 - 512)
+
+#define ERASE_MARK 0x3c69
+#define SECTOR_FREE 0xff
+#define SECTOR_USED 0x55
+#define SECTOR_IGNORE 0x11
+#define SECTOR_DELETED 0x00
+
+#define FOLD_MARK_IN_PROGRESS 0x5555
+
+#define ZONE_GOOD 0xff
+#define ZONE_BAD_ORIGINAL 0
+#define ZONE_BAD_MARKED 7
+
+
+#endif /* __MTD_NFTL_USER_H__ */