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, 90 insertions, 0 deletions

diff --git a/tools/perf/ui/util.c b/tools/perf/ui/util.c
new file mode 100644
index 000000000..1d38ddf01
--- /dev/null
+++ b/tools/perf/ui/util.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "util.h"
+#include "../util/debug.h"
+#include <stdio.h>
+
+/*
+ * Default error logging functions
+ */
+static int perf_stdio__error(const char *format, va_list args)
+{
+	fprintf(stderr, "Error:\n");
+	vfprintf(stderr, format, args);
+	return 0;
+}
+
+static int perf_stdio__warning(const char *format, va_list args)
+{
+	if (quiet)
+		return 0;
+
+	fprintf(stderr, "Warning:\n");
+	vfprintf(stderr, format, args);
+	return 0;
+}
+
+static struct perf_error_ops default_eops =
+{
+	.error		= perf_stdio__error,
+	.warning	= perf_stdio__warning,
+};
+
+static struct perf_error_ops *perf_eops = &default_eops;
+
+
+int ui__error(const char *format, ...)
+{
+	int ret;
+	va_list args;
+
+	va_start(args, format);
+	ret = perf_eops->error(format, args);
+	va_end(args);
+
+	return ret;
+}
+
+int ui__warning(const char *format, ...)
+{
+	int ret;
+	va_list args;
+	if (quiet)
+		return 0;
+
+	va_start(args, format);
+	ret = perf_eops->warning(format, args);
+	va_end(args);
+
+	return ret;
+}
+
+/**
+ * perf_error__register - Register error logging functions
+ * @eops: The pointer to error logging function struct
+ *
+ * Register UI-specific error logging functions. Before calling this,
+ * other logging functions should be unregistered, if any.
+ */
+int perf_error__register(struct perf_error_ops *eops)
+{
+	if (perf_eops != &default_eops)
+		return -1;
+
+	perf_eops = eops;
+	return 0;
+}
+
+/**
+ * perf_error__unregister - Unregister error logging functions
+ * @eops: The pointer to error logging function struct
+ *
+ * Unregister already registered error logging functions.
+ */
+int perf_error__unregister(struct perf_error_ops *eops)
+{
+	if (perf_eops != eops)
+		return -1;
+
+	perf_eops = &default_eops;
+	return 0;
+}