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, 332 insertions, 0 deletions

diff --git a/tools/perf/util/block-range.c b/tools/perf/util/block-range.c
new file mode 100644
index 000000000..7c559fcfd
--- /dev/null
+++ b/tools/perf/util/block-range.c
@@ -0,0 +1,332 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "block-range.h"
+#include "annotate.h"
+#include <assert.h>
+#include <stdlib.h>
+
+static struct {
+	struct rb_root root;
+	u64 blocks;
+} block_ranges;
+
+static void block_range__debug(void)
+{
+#ifndef NDEBUG
+	struct rb_node *rb;
+	u64 old = 0; /* NULL isn't executable */
+
+	for (rb = rb_first(&block_ranges.root); rb; rb = rb_next(rb)) {
+		struct block_range *entry = rb_entry(rb, struct block_range, node);
+
+		assert(old < entry->start);
+		assert(entry->start <= entry->end); /* single instruction block; jump to a jump */
+
+		old = entry->end;
+	}
+#endif
+}
+
+struct block_range *block_range__find(u64 addr)
+{
+	struct rb_node **p = &block_ranges.root.rb_node;
+	struct rb_node *parent = NULL;
+	struct block_range *entry;
+
+	while (*p != NULL) {
+		parent = *p;
+		entry = rb_entry(parent, struct block_range, node);
+
+		if (addr < entry->start)
+			p = &parent->rb_left;
+		else if (addr > entry->end)
+			p = &parent->rb_right;
+		else
+			return entry;
+	}
+
+	return NULL;
+}
+
+static inline void rb_link_left_of_node(struct rb_node *left, struct rb_node *node)
+{
+	struct rb_node **p = &node->rb_left;
+	while (*p) {
+		node = *p;
+		p = &node->rb_right;
+	}
+	rb_link_node(left, node, p);
+}
+
+static inline void rb_link_right_of_node(struct rb_node *right, struct rb_node *node)
+{
+	struct rb_node **p = &node->rb_right;
+	while (*p) {
+		node = *p;
+		p = &node->rb_left;
+	}
+	rb_link_node(right, node, p);
+}
+
+/**
+ * block_range__create
+ * @start: branch target starting this basic block
+ * @end:   branch ending this basic block
+ *
+ * Create all the required block ranges to precisely span the given range.
+ */
+struct block_range_iter block_range__create(u64 start, u64 end)
+{
+	struct rb_node **p = &block_ranges.root.rb_node;
+	struct rb_node *n, *parent = NULL;
+	struct block_range *next, *entry = NULL;
+	struct block_range_iter iter = { NULL, NULL };
+
+	while (*p != NULL) {
+		parent = *p;
+		entry = rb_entry(parent, struct block_range, node);
+
+		if (start < entry->start)
+			p = &parent->rb_left;
+		else if (start > entry->end)
+			p = &parent->rb_right;
+		else
+			break;
+	}
+
+	/*
+	 * Didn't find anything.. there's a hole at @start, however @end might
+	 * be inside/behind the next range.
+	 */
+	if (!*p) {
+		if (!entry) /* tree empty */
+			goto do_whole;
+
+		/*
+		 * If the last node is before, advance one to find the next.
+		 */
+		n = parent;
+		if (entry->end < start) {
+			n = rb_next(n);
+			if (!n)
+				goto do_whole;
+		}
+		next = rb_entry(n, struct block_range, node);
+
+		if (next->start <= end) { /* add head: [start...][n->start...] */
+			struct block_range *head = malloc(sizeof(struct block_range));
+			if (!head)
+				return iter;
+
+			*head = (struct block_range){
+				.start		= start,
+				.end		= next->start - 1,
+				.is_target	= 1,
+				.is_branch	= 0,
+			};
+
+			rb_link_left_of_node(&head->node, &next->node);
+			rb_insert_color(&head->node, &block_ranges.root);
+			block_range__debug();
+
+			iter.start = head;
+			goto do_tail;
+		}
+
+do_whole:
+		/*
+		 * The whole [start..end] range is non-overlapping.
+		 */
+		entry = malloc(sizeof(struct block_range));
+		if (!entry)
+			return iter;
+
+		*entry = (struct block_range){
+			.start		= start,
+			.end		= end,
+			.is_target	= 1,
+			.is_branch	= 1,
+		};
+
+		rb_link_node(&entry->node, parent, p);
+		rb_insert_color(&entry->node, &block_ranges.root);
+		block_range__debug();
+
+		iter.start = entry;
+		iter.end   = entry;
+		goto done;
+	}
+
+	/*
+	 * We found a range that overlapped with ours, split if needed.
+	 */
+	if (entry->start < start) { /* split: [e->start...][start...] */
+		struct block_range *head = malloc(sizeof(struct block_range));
+		if (!head)
+			return iter;
+
+		*head = (struct block_range){
+			.start		= entry->start,
+			.end		= start - 1,
+			.is_target	= entry->is_target,
+			.is_branch	= 0,
+
+			.coverage	= entry->coverage,
+			.entry		= entry->entry,
+		};
+
+		entry->start		= start;
+		entry->is_target	= 1;
+		entry->entry		= 0;
+
+		rb_link_left_of_node(&head->node, &entry->node);
+		rb_insert_color(&head->node, &block_ranges.root);
+		block_range__debug();
+
+	} else if (entry->start == start)
+		entry->is_target = 1;
+
+	iter.start = entry;
+
+do_tail:
+	/*
+	 * At this point we've got: @iter.start = [@start...] but @end can still be
+	 * inside or beyond it.
+	 */
+	entry = iter.start;
+	for (;;) {
+		/*
+		 * If @end is inside @entry, split.
+		 */
+		if (end < entry->end) { /* split: [...end][...e->end] */
+			struct block_range *tail = malloc(sizeof(struct block_range));
+			if (!tail)
+				return iter;
+
+			*tail = (struct block_range){
+				.start		= end + 1,
+				.end		= entry->end,
+				.is_target	= 0,
+				.is_branch	= entry->is_branch,
+
+				.coverage	= entry->coverage,
+				.taken		= entry->taken,
+				.pred		= entry->pred,
+			};
+
+			entry->end		= end;
+			entry->is_branch	= 1;
+			entry->taken		= 0;
+			entry->pred		= 0;
+
+			rb_link_right_of_node(&tail->node, &entry->node);
+			rb_insert_color(&tail->node, &block_ranges.root);
+			block_range__debug();
+
+			iter.end = entry;
+			goto done;
+		}
+
+		/*
+		 * If @end matches @entry, done
+		 */
+		if (end == entry->end) {
+			entry->is_branch = 1;
+			iter.end = entry;
+			goto done;
+		}
+
+		next = block_range__next(entry);
+		if (!next)
+			goto add_tail;
+
+		/*
+		 * If @end is in beyond @entry but not inside @next, add tail.
+		 */
+		if (end < next->start) { /* add tail: [...e->end][...end] */
+			struct block_range *tail;
+add_tail:
+			tail = malloc(sizeof(struct block_range));
+			if (!tail)
+				return iter;
+
+			*tail = (struct block_range){
+				.start		= entry->end + 1,
+				.end		= end,
+				.is_target	= 0,
+				.is_branch	= 1,
+			};
+
+			rb_link_right_of_node(&tail->node, &entry->node);
+			rb_insert_color(&tail->node, &block_ranges.root);
+			block_range__debug();
+
+			iter.end = tail;
+			goto done;
+		}
+
+		/*
+		 * If there is a hole between @entry and @next, fill it.
+		 */
+		if (entry->end + 1 != next->start) {
+			struct block_range *hole = malloc(sizeof(struct block_range));
+			if (!hole)
+				return iter;
+
+			*hole = (struct block_range){
+				.start		= entry->end + 1,
+				.end		= next->start - 1,
+				.is_target	= 0,
+				.is_branch	= 0,
+			};
+
+			rb_link_left_of_node(&hole->node, &next->node);
+			rb_insert_color(&hole->node, &block_ranges.root);
+			block_range__debug();
+		}
+
+		entry = next;
+	}
+
+done:
+	assert(iter.start->start == start && iter.start->is_target);
+	assert(iter.end->end == end && iter.end->is_branch);
+
+	block_ranges.blocks++;
+
+	return iter;
+}
+
+
+/*
+ * Compute coverage as:
+ *
+ *    br->coverage / br->sym->max_coverage
+ *
+ * This ensures each symbol has a 100% spot, to reflect that each symbol has a
+ * most covered section.
+ *
+ * Returns [0-1] for coverage and -1 if we had no data what so ever or the
+ * symbol does not exist.
+ */
+double block_range__coverage(struct block_range *br)
+{
+	struct symbol *sym;
+	struct annotated_branch *branch;
+
+	if (!br) {
+		if (block_ranges.blocks)
+			return 0;
+
+		return -1;
+	}
+
+	sym = br->sym;
+	if (!sym)
+		return -1;
+
+	branch = symbol__annotation(sym)->branch;
+	if (!branch)
+		return -1;
+
+	return (double)br->coverage / branch->max_coverage;
+}