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, 111 insertions, 0 deletions

diff --git a/samples/bpf/sock_example.c b/samples/bpf/sock_example.c
new file mode 100644
index 000000000..5b66f2401
--- /dev/null
+++ b/samples/bpf/sock_example.c
@@ -0,0 +1,111 @@
+/* eBPF example program:
+ * - creates arraymap in kernel with key 4 bytes and value 8 bytes
+ *
+ * - loads eBPF program:
+ *   r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)];
+ *   *(u32*)(fp - 4) = r0;
+ *   // assuming packet is IPv4, lookup ip->proto in a map
+ *   value = bpf_map_lookup_elem(map_fd, fp - 4);
+ *   if (value)
+ *        (*(u64*)value) += 1;
+ *
+ * - attaches this program to loopback interface "lo" raw socket
+ *
+ * - every second user space reads map[tcp], map[udp], map[icmp] to see
+ *   how many packets of given protocol were seen on "lo"
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <assert.h>
+#include <linux/bpf.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+#include <stddef.h>
+#include <bpf/bpf.h>
+#include "bpf_insn.h"
+#include "sock_example.h"
+#include "bpf_util.h"
+
+char bpf_log_buf[BPF_LOG_BUF_SIZE];
+
+static int test_sock(void)
+{
+	int sock = -1, map_fd, prog_fd, i, key;
+	long long value = 0, tcp_cnt, udp_cnt, icmp_cnt;
+
+	map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, NULL, sizeof(key), sizeof(value),
+				256, NULL);
+	if (map_fd < 0) {
+		printf("failed to create map '%s'\n", strerror(errno));
+		goto cleanup;
+	}
+
+	struct bpf_insn prog[] = {
+		BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+		BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol) /* R0 = ip->proto */),
+		BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
+		BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+		BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
+		BPF_LD_MAP_FD(BPF_REG_1, map_fd),
+		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
+		BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
+		BPF_ATOMIC_OP(BPF_DW, BPF_ADD, BPF_REG_0, BPF_REG_1, 0),
+		BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
+		BPF_EXIT_INSN(),
+	};
+	size_t insns_cnt = ARRAY_SIZE(prog);
+	LIBBPF_OPTS(bpf_prog_load_opts, opts,
+		.log_buf = bpf_log_buf,
+		.log_size = BPF_LOG_BUF_SIZE,
+	);
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL",
+				prog, insns_cnt, &opts);
+	if (prog_fd < 0) {
+		printf("failed to load prog '%s'\n", strerror(errno));
+		goto cleanup;
+	}
+
+	sock = open_raw_sock("lo");
+
+	if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
+		       sizeof(prog_fd)) < 0) {
+		printf("setsockopt %s\n", strerror(errno));
+		goto cleanup;
+	}
+
+	for (i = 0; i < 10; i++) {
+		key = IPPROTO_TCP;
+		assert(bpf_map_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
+
+		key = IPPROTO_UDP;
+		assert(bpf_map_lookup_elem(map_fd, &key, &udp_cnt) == 0);
+
+		key = IPPROTO_ICMP;
+		assert(bpf_map_lookup_elem(map_fd, &key, &icmp_cnt) == 0);
+
+		printf("TCP %lld UDP %lld ICMP %lld packets\n",
+		       tcp_cnt, udp_cnt, icmp_cnt);
+		sleep(1);
+	}
+
+cleanup:
+	/* maps, programs, raw sockets will auto cleanup on process exit */
+	return 0;
+}
+
+int main(void)
+{
+	FILE *f;
+
+	f = popen("ping -4 -c5 localhost", "r");
+	(void)f;
+
+	return test_sock();
+}