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, 26 insertions, 0 deletions

diff --git a/io_uring/uring_cmd.h b/io_uring/uring_cmd.h
new file mode 100644
index 000000000..041aef8a8
--- /dev/null
+++ b/io_uring/uring_cmd.h
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/io_uring/cmd.h>
+#include <linux/io_uring_types.h>
+
+struct io_async_cmd {
+	struct iou_vec			vec;
+	struct io_uring_sqe		sqes[2];
+};
+
+int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags);
+int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+void io_uring_cmd_sqe_copy(struct io_kiocb *req);
+void io_uring_cmd_cleanup(struct io_kiocb *req);
+
+bool io_uring_try_cancel_uring_cmd(struct io_ring_ctx *ctx,
+				   struct io_uring_task *tctx, bool cancel_all);
+
+bool io_uring_cmd_post_mshot_cqe32(struct io_uring_cmd *cmd,
+				   unsigned int issue_flags,
+				   struct io_uring_cqe cqe[2]);
+
+void io_cmd_cache_free(const void *entry);
+
+int io_cmd_poll_multishot(struct io_uring_cmd *cmd,
+			  unsigned int issue_flags, __poll_t mask);