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, 51 insertions, 0 deletions

diff --git a/tools/perf/util/time-utils.h b/tools/perf/util/time-utils.h
new file mode 100644
index 000000000..1142b0bdd
--- /dev/null
+++ b/tools/perf/util/time-utils.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _TIME_UTILS_H_
+#define _TIME_UTILS_H_
+
+#include <stddef.h>
+#include <time.h>
+#include <linux/types.h>
+
+struct perf_time_interval {
+	u64 start, end;
+};
+
+int parse_nsec_time(const char *str, u64 *ptime);
+
+int perf_time__parse_str(struct perf_time_interval *ptime, const char *ostr);
+
+int perf_time__percent_parse_str(struct perf_time_interval *ptime_buf, int num,
+				 const char *ostr, u64 start, u64 end);
+
+struct perf_time_interval *perf_time__range_alloc(const char *ostr, int *size);
+
+bool perf_time__skip_sample(struct perf_time_interval *ptime, u64 timestamp);
+
+bool perf_time__ranges_skip_sample(struct perf_time_interval *ptime_buf,
+				   int num, u64 timestamp);
+
+struct perf_session;
+
+int perf_time__parse_for_ranges_reltime(const char *str, struct perf_session *session,
+				struct perf_time_interval **ranges,
+				int *range_size, int *range_num,
+				bool reltime);
+
+int perf_time__parse_for_ranges(const char *str, struct perf_session *session,
+				struct perf_time_interval **ranges,
+				int *range_size, int *range_num);
+
+int timestamp__scnprintf_usec(u64 timestamp, char *buf, size_t sz);
+int timestamp__scnprintf_nsec(u64 timestamp, char *buf, size_t sz);
+
+int fetch_current_timestamp(char *buf, size_t sz);
+
+static inline unsigned long long rdclock(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return ts.tv_sec * 1000000000ULL + ts.tv_nsec;
+}
+
+#endif