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/rdma/opa_addr.h b/include/rdma/opa_addr.h
new file mode 100644
index 000000000..c6bfa2640
--- /dev/null
+++ b/include/rdma/opa_addr.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause */
+/*
+ * Copyright(c) 2017 Intel Corporation.
+ */
+
+#ifndef OPA_ADDR_H
+#define OPA_ADDR_H
+
+#include <rdma/opa_smi.h>
+
+#define	OPA_SPECIAL_OUI		(0x00066AULL)
+#define OPA_MAKE_ID(x)          (cpu_to_be64(OPA_SPECIAL_OUI << 40 | (x)))
+#define OPA_TO_IB_UCAST_LID(x) (((x) >= be16_to_cpu(IB_MULTICAST_LID_BASE)) \
+				? 0 : x)
+#define OPA_GID_INDEX		0x1
+/**
+ * 0xF8 - 4 bits of multicast range and 1 bit for collective range
+ * Example: For 24 bit LID space,
+ * Multicast range: 0xF00000 to 0xF7FFFF
+ * Collective range: 0xF80000 to 0xFFFFFE
+ */
+#define OPA_MCAST_NR 0x4 /* Number of top bits set */
+#define OPA_COLLECTIVE_NR 0x1 /* Number of bits after MCAST_NR */
+
+/**
+ * ib_is_opa_gid: Returns true if the top 24 bits of the gid
+ * contains the OPA_STL_OUI identifier. This identifies that
+ * the provided gid is a special purpose GID meant to carry
+ * extended LID information.
+ *
+ * @gid: The Global identifier
+ */
+static inline bool ib_is_opa_gid(const union ib_gid *gid)
+{
+	return ((be64_to_cpu(gid->global.interface_id) >> 40) ==
+		OPA_SPECIAL_OUI);
+}
+
+/**
+ * opa_get_lid_from_gid: Returns the last 32 bits of the gid.
+ * OPA devices use one of the gids in the gid table to also
+ * store the lid.
+ *
+ * @gid: The Global identifier
+ */
+static inline u32 opa_get_lid_from_gid(const union ib_gid *gid)
+{
+	return be64_to_cpu(gid->global.interface_id) & 0xFFFFFFFF;
+}
+
+/**
+ * opa_is_extended_lid: Returns true if dlid or slid are
+ * extended.
+ *
+ * @dlid: The DLID
+ * @slid: The SLID
+ */
+static inline bool opa_is_extended_lid(__be32 dlid, __be32 slid)
+{
+	if ((be32_to_cpu(dlid) >=
+	     be16_to_cpu(IB_MULTICAST_LID_BASE)) ||
+	    (be32_to_cpu(slid) >=
+	     be16_to_cpu(IB_MULTICAST_LID_BASE)))
+		return true;
+
+	return false;
+}
+
+/* Get multicast lid base */
+static inline u32 opa_get_mcast_base(u32 nr_top_bits)
+{
+	return (be32_to_cpu(OPA_LID_PERMISSIVE) << (32 - nr_top_bits));
+}
+
+/* Check for a valid unicast LID for non-SM traffic types */
+static inline bool rdma_is_valid_unicast_lid(struct rdma_ah_attr *attr)
+{
+	if (attr->type == RDMA_AH_ATTR_TYPE_IB) {
+		if (!rdma_ah_get_dlid(attr) ||
+		    rdma_ah_get_dlid(attr) >=
+		    be16_to_cpu(IB_MULTICAST_LID_BASE))
+			return false;
+	} else if (attr->type == RDMA_AH_ATTR_TYPE_OPA) {
+		if (!rdma_ah_get_dlid(attr) ||
+		    rdma_ah_get_dlid(attr) >=
+		    opa_get_mcast_base(OPA_MCAST_NR))
+			return false;
+	}
+	return true;
+}
+#endif /* OPA_ADDR_H */