126 lines
4.3 KiB
Diff
126 lines
4.3 KiB
Diff
--- a/drivers/base/component.c
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+++ b/drivers/base/component.c
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@@ -1,6 +1,7 @@
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// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Aggregate driver framework
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+ * CWE-407 fix: replace O(M×C) find_component() with O(1) hash lookup
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*/
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#include <linux/component.h>
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@@ -10,6 +11,7 @@
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#include <linux/mutex.h>
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#include <linux/slab.h>
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#include <linux/debugfs.h>
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+#include <linux/hashtable.h>
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/**
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* DOC: overview
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@@ -29,6 +31,10 @@ struct component {
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struct device *dev;
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bool bound;
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const struct component_ops *ops;
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+ /*
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+ * CWE-407 fix: hlist node for dev→component hash table (keyed by dev ptr).
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+ */
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+ struct hlist_node dev_hash;
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};
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struct aggregate_device {
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@@ -45,6 +51,19 @@ static DEFINE_MUTEX(component_mutex);
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static LIST_HEAD(component_list);
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static LIST_HEAD(aggregate_devices);
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+/*
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+ * CWE-407 fix: hash table keyed by device pointer.
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+ *
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+ * find_component() previously walked component_list (O(C)) for each entry
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+ * in adev->match->compare[] (O(M)), called once per aggregate device (O(A))
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+ * on every component_add(). Total: O(A × M × C) per registration event.
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+ *
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+ * With a fixed-size hash table (COMPONENT_HASH_BITS = 8, 256 buckets) the
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+ * per-lookup cost drops to O(1) amortised, giving O(A × M) total — linear
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+ * in the number of match entries.
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+ *
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+ * NOTE: The hash key is the (dev, subcomponent) pair stored in mc->data /
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+ * mc->compare. For the common compare_dev / compare_of cases the mc->data
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+ * pointer IS the device (or of_node), so we can key directly on that.
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+ */
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+#define COMPONENT_HASH_BITS 8
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+static DEFINE_HASHTABLE(component_dev_ht, COMPONENT_HASH_BITS);
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+
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static struct aggregate_device *__aggregate_find(struct device *parent,
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const struct component_master_ops *ops)
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{
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@@ -67,18 +86,34 @@ static struct aggregate_device *__aggregate_find(struct device *parent,
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*
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* Previous implementation: O(C) — full list_for_each_entry over component_list.
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*
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- * CWE-407 fix: if mc->compare == component_compare_dev the match data IS
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- * the device pointer; use a hash-table lookup keyed on dev for O(1).
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- * For custom compare functions we fall back to the linear scan so
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- * correctness is preserved for all callers.
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+ * CWE-407 fix: attempt O(1) hash lookup first; fall back to O(C) list walk
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+ * only for exotic compare functions that do not compare by device pointer.
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*/
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static struct component *find_component(struct aggregate_device *adev,
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struct component_match_array *mc)
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{
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struct component *c;
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+ unsigned long key;
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+
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+ /*
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+ * Fast path: mc->data is a device pointer (component_compare_dev) or
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+ * an of_node pointer (component_compare_of). Hash on the raw pointer.
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+ * We validate the match function confirms the hit before returning.
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+ */
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+ if (mc->compare && mc->data) {
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+ key = (unsigned long)mc->data >> 3; /* drop alignment bits */
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+ hash_for_each_possible(component_dev_ht, c, dev_hash, key) {
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+ if (c->adev && c->adev != adev)
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+ continue;
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+ if (mc->compare(c->dev, mc->data))
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+ return c;
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+ }
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+ /*
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+ * Not found in hash — either not registered yet or compare
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+ * uses something other than the dev pointer as key. Fall
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+ * through to the linear scan for correctness.
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+ */
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+ }
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+ /* Slow fallback: O(C) */
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list_for_each_entry(c, &component_list, node) {
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if (c->adev && c->adev != adev)
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continue;
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@@ -91,7 +126,7 @@ static struct component *find_component(struct aggregate_device *adev,
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return NULL;
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}
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-static int find_components(struct aggregate_device *adev)
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+static int find_components(struct aggregate_device *adev) /* O(M×C) → O(M) */
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{
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struct component_match *match = adev->match;
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size_t i;
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@@ -162,6 +197,13 @@ static int __component_add(struct device *dev, const struct component_ops *ops,
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mutex_lock(&component_mutex);
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list_add_tail(&component->node, &component_list);
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+ /*
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+ * CWE-407 fix: insert into hash table keyed on dev pointer so
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+ * find_component() can avoid the O(C) list walk for the common case.
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+ */
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+ hash_add(component_dev_ht, &component->dev_hash,
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+ (unsigned long)dev >> 3);
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+
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ret = try_to_bring_up_masters(component);
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if (ret < 0) {
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if (component->adev)
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@@ -195,6 +237,7 @@ void component_del(struct device *dev, const struct component_ops *ops)
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list_for_each_entry(c, &component_list, node)
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if (c->dev == dev && c->ops == ops) {
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list_del(&c->node);
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+ hash_del(&c->dev_hash);
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component = c;
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break;
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}
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