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https://github.com/GrapheneOS/hardened_malloc.git
synced 2024-10-01 01:36:01 -04:00
randomize slab slot choice
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parent
965c3202b4
commit
f08d4d31db
22
malloc.c
22
malloc.c
@ -248,19 +248,35 @@ static bool get_slot(struct slab_metadata *metadata, size_t index) {
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}
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static uint64_t get_mask(size_t slots) {
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if (slots > 64) return 0; // TODO: implement multi-word bitmaps
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return slots < 64 ? ~0UL << slots : 0;
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}
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static size_t first_free_slot(size_t slots, struct slab_metadata *metadata) {
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static size_t get_free_slot(struct random_state *rng, size_t slots, struct slab_metadata *metadata) {
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if (slots > 64) {
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slots = 64;
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}
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uint64_t masked = metadata->bitmap | get_mask(slots);
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if (masked == ~0UL) {
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fatal_error("no zero bits");
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}
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// randomize start location for linear search (uniform random choice is too slow)
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uint64_t random_split = ~0UL >> get_random_size_uniform(rng, slots);
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size_t slot = __builtin_ffsl(~(masked | random_split));
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if (slot) {
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return slot - 1;
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} else {
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return __builtin_ffsl(~masked) - 1;
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}
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}
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static bool has_free_slots(size_t slots, struct slab_metadata *metadata) {
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if (slots > 64) {
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slots = 64;
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}
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uint64_t masked = metadata->bitmap | get_mask(slots);
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return masked != ~0UL;
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}
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@ -348,7 +364,7 @@ static void *slab_allocate(size_t requested_size) {
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}
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struct slab_metadata *metadata = c->partial_slabs;
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size_t slot = first_free_slot(slots, metadata);
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size_t slot = get_free_slot(&c->rng, slots, metadata);
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set_slot(metadata, slot);
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if (!has_free_slots(slots, metadata)) {
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