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, 97 insertions, 0 deletions

diff --git a/drivers/net/netdevsim/tc.c b/drivers/net/netdevsim/tc.c
new file mode 100644
index 000000000..a415e02a6
--- /dev/null
+++ b/drivers/net/netdevsim/tc.c
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/netdevice.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+
+#include "netdevsim.h"
+
+static int
+nsim_setup_tc_block_cb(enum tc_setup_type type, void *type_data, void *cb_priv)
+{
+	struct flow_cls_common_offload *common = type_data;
+	int err = 0;
+
+	switch (type) {
+	case TC_SETUP_CLSBPF:
+		err = nsim_bpf_setup_tc_block_cb(type, type_data, cb_priv);
+		break;
+	case TC_SETUP_CLSFLOWER:
+		break;
+	default:
+		NSIM_EA(common->extack, "offload type not supported");
+		err = -EOPNOTSUPP;
+		break;
+	}
+
+	return err;
+}
+
+static void nsim_taprio_stats(struct tc_taprio_qopt_stats *stats)
+{
+	stats->window_drops = 0;
+	stats->tx_overruns = 0;
+}
+
+static int nsim_setup_tc_taprio(struct net_device *dev,
+				struct tc_taprio_qopt_offload *offload)
+{
+	int err = 0;
+
+	switch (offload->cmd) {
+	case TAPRIO_CMD_REPLACE:
+	case TAPRIO_CMD_DESTROY:
+		break;
+	case TAPRIO_CMD_STATS:
+		nsim_taprio_stats(&offload->stats);
+		break;
+	default:
+		err = -EOPNOTSUPP;
+	}
+
+	return err;
+}
+
+static int nsim_setup_tc_ets(struct net_device *dev,
+			     struct tc_ets_qopt_offload *offload)
+{
+	int err = 0;
+
+	switch (offload->command) {
+	case TC_ETS_REPLACE:
+	case TC_ETS_DESTROY:
+		break;
+	case TC_ETS_STATS:
+		_bstats_update(offload->stats.bstats, 0, 0);
+		break;
+	default:
+		err = -EOPNOTSUPP;
+	}
+
+	return err;
+}
+
+static LIST_HEAD(nsim_block_cb_list);
+
+int
+nsim_setup_tc(struct net_device *dev, enum tc_setup_type type, void *type_data)
+{
+	struct netdevsim *ns = netdev_priv(dev);
+
+	switch (type) {
+	case TC_SETUP_QDISC_TAPRIO:
+		return nsim_setup_tc_taprio(dev, type_data);
+	case TC_SETUP_QDISC_ETS:
+		return nsim_setup_tc_ets(dev, type_data);
+	case TC_SETUP_BLOCK:
+		return flow_block_cb_setup_simple(type_data,
+						  &nsim_block_cb_list,
+						  nsim_setup_tc_block_cb,
+						  ns, ns, true);
+	case TC_SETUP_FT:
+		return 0;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+ALLOW_ERROR_INJECTION(nsim_setup_tc, ERRNO);