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, 64 insertions, 0 deletions

diff --git a/tools/perf/util/expr.h b/tools/perf/util/expr.h
new file mode 100644
index 000000000..ed12e4007
--- /dev/null
+++ b/tools/perf/util/expr.h
@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef PARSE_CTX_H
+#define PARSE_CTX_H 1
+
+struct hashmap;
+struct metric_ref;
+
+struct expr_scanner_ctx {
+	char *user_requested_cpu_list;
+	int runtime;
+	bool system_wide;
+	bool is_test;
+};
+
+struct expr_parse_ctx {
+	struct hashmap	*ids;
+	struct expr_scanner_ctx sctx;
+};
+
+struct expr_id_data;
+
+struct hashmap *ids__new(void);
+void ids__free(struct hashmap *ids);
+int ids__insert(struct hashmap *ids, const char *id);
+/*
+ * Union two sets of ids (hashmaps) and construct a third, freeing ids1 and
+ * ids2.
+ */
+struct hashmap *ids__union(struct hashmap *ids1, struct hashmap *ids2);
+
+struct expr_parse_ctx *expr__ctx_new(void);
+void expr__ctx_clear(struct expr_parse_ctx *ctx);
+void expr__ctx_free(struct expr_parse_ctx *ctx);
+
+void expr__del_id(struct expr_parse_ctx *ctx, const char *id);
+int expr__add_id(struct expr_parse_ctx *ctx, const char *id);
+int expr__add_id_val(struct expr_parse_ctx *ctx, const char *id, double val);
+int expr__add_id_val_source_count(struct expr_parse_ctx *ctx, const char *id,
+				  double val, int source_count);
+int expr__add_id_val_source_count_aggr_nr(struct expr_parse_ctx *ctx, const char *id,
+					  double val, int source_count, int aggr_nr);
+int expr__add_ref(struct expr_parse_ctx *ctx, struct metric_ref *ref);
+int expr__get_id(struct expr_parse_ctx *ctx, const char *id,
+		 struct expr_id_data **data);
+bool expr__subset_of_ids(struct expr_parse_ctx *haystack,
+			 struct expr_parse_ctx *needles);
+int expr__resolve_id(struct expr_parse_ctx *ctx, const char *id,
+		     struct expr_id_data **datap);
+
+int expr__parse(double *final_val, struct expr_parse_ctx *ctx,
+		const char *expr);
+
+int expr__find_ids(const char *expr, const char *one,
+		   struct expr_parse_ctx *ids);
+
+double expr_id_data__value(const struct expr_id_data *data);
+double expr_id_data__source_count(const struct expr_id_data *data);
+double expr_id_data__aggr_nr(const struct expr_id_data *data);
+
+double expr__get_literal(const char *literal, const struct expr_scanner_ctx *ctx);
+double expr__has_event(const struct expr_parse_ctx *ctx, bool compute_ids, const char *id);
+double expr__strcmp_cpuid_str(const struct expr_parse_ctx *ctx, bool compute_ids, const char *id);
+
+#endif