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, 149 insertions, 0 deletions

diff --git a/io_uring/splice.c b/io_uring/splice.c
new file mode 100644
index 000000000..e81ebbb91
--- /dev/null
+++ b/io_uring/splice.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/namei.h>
+#include <linux/io_uring.h>
+#include <linux/splice.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "filetable.h"
+#include "io_uring.h"
+#include "splice.h"
+
+struct io_splice {
+	struct file			*file_out;
+	loff_t				off_out;
+	loff_t				off_in;
+	u64				len;
+	int				splice_fd_in;
+	unsigned int			flags;
+	struct io_rsrc_node		*rsrc_node;
+};
+
+static int __io_splice_prep(struct io_kiocb *req,
+			    const struct io_uring_sqe *sqe)
+{
+	struct io_splice *sp = io_kiocb_to_cmd(req, struct io_splice);
+	unsigned int valid_flags = SPLICE_F_FD_IN_FIXED | SPLICE_F_ALL;
+
+	sp->len = READ_ONCE(sqe->len);
+	sp->flags = READ_ONCE(sqe->splice_flags);
+	if (unlikely(sp->flags & ~valid_flags))
+		return -EINVAL;
+	sp->splice_fd_in = READ_ONCE(sqe->splice_fd_in);
+	sp->rsrc_node = NULL;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_tee_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	if (READ_ONCE(sqe->splice_off_in) || READ_ONCE(sqe->off))
+		return -EINVAL;
+	return __io_splice_prep(req, sqe);
+}
+
+void io_splice_cleanup(struct io_kiocb *req)
+{
+	struct io_splice *sp = io_kiocb_to_cmd(req, struct io_splice);
+
+	if (sp->rsrc_node)
+		io_put_rsrc_node(req->ctx, sp->rsrc_node);
+}
+
+static struct file *io_splice_get_file(struct io_kiocb *req,
+				       unsigned int issue_flags)
+{
+	struct io_splice *sp = io_kiocb_to_cmd(req, struct io_splice);
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_rsrc_node *node;
+	struct file *file = NULL;
+
+	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
+		return io_file_get_normal(req, sp->splice_fd_in);
+
+	io_ring_submit_lock(ctx, issue_flags);
+	node = io_rsrc_node_lookup(&ctx->file_table.data, sp->splice_fd_in);
+	if (node) {
+		node->refs++;
+		sp->rsrc_node = node;
+		file = io_slot_file(node);
+		req->flags |= REQ_F_NEED_CLEANUP;
+	}
+	io_ring_submit_unlock(ctx, issue_flags);
+	return file;
+}
+
+int io_tee(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_splice *sp = io_kiocb_to_cmd(req, struct io_splice);
+	struct file *out = sp->file_out;
+	unsigned int flags = sp->flags & ~SPLICE_F_FD_IN_FIXED;
+	struct file *in;
+	ssize_t ret = 0;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	in = io_splice_get_file(req, issue_flags);
+	if (!in) {
+		ret = -EBADF;
+		goto done;
+	}
+
+	if (sp->len)
+		ret = do_tee(in, out, sp->len, flags);
+
+	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
+		fput(in);
+done:
+	if (ret != sp->len)
+		req_set_fail(req);
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+int io_splice_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_splice *sp = io_kiocb_to_cmd(req, struct io_splice);
+
+	sp->off_in = READ_ONCE(sqe->splice_off_in);
+	sp->off_out = READ_ONCE(sqe->off);
+	return __io_splice_prep(req, sqe);
+}
+
+int io_splice(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_splice *sp = io_kiocb_to_cmd(req, struct io_splice);
+	struct file *out = sp->file_out;
+	unsigned int flags = sp->flags & ~SPLICE_F_FD_IN_FIXED;
+	loff_t *poff_in, *poff_out;
+	struct file *in;
+	ssize_t ret = 0;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	in = io_splice_get_file(req, issue_flags);
+	if (!in) {
+		ret = -EBADF;
+		goto done;
+	}
+
+	poff_in = (sp->off_in == -1) ? NULL : &sp->off_in;
+	poff_out = (sp->off_out == -1) ? NULL : &sp->off_out;
+
+	if (sp->len)
+		ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);
+
+	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
+		fput(in);
+done:
+	if (ret != sp->len)
+		req_set_fail(req);
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}