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, 27 insertions, 0 deletions

diff --git a/sound/firewire/packets-buffer.h b/sound/firewire/packets-buffer.h
new file mode 100644
index 000000000..99e963c27
--- /dev/null
+++ b/sound/firewire/packets-buffer.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef SOUND_FIREWIRE_PACKETS_BUFFER_H_INCLUDED
+#define SOUND_FIREWIRE_PACKETS_BUFFER_H_INCLUDED
+
+#include <linux/dma-mapping.h>
+#include <linux/firewire.h>
+
+/**
+ * struct iso_packets_buffer - manages a buffer for many packets
+ * @iso_buffer: the memory containing the packets
+ * @packets: an array, with each element pointing to one packet
+ */
+struct iso_packets_buffer {
+	struct fw_iso_buffer iso_buffer;
+	struct {
+		void *buffer;
+		unsigned int offset;
+	} *packets;
+};
+
+int iso_packets_buffer_init(struct iso_packets_buffer *b, struct fw_unit *unit,
+			    unsigned int count, unsigned int packet_size,
+			    enum dma_data_direction direction);
+void iso_packets_buffer_destroy(struct iso_packets_buffer *b,
+				struct fw_unit *unit);
+
+#endif