Commit 870ff192 authored by Pimyn Girgis's avatar Pimyn Girgis Committed by Andrew Morton
Browse files

mm/kfence: randomize the freelist on initialization 

Randomize the KFENCE freelist during pool initialization to make
allocation patterns less predictable.  This is achieved by shuffling the
order in which metadata objects are added to the freelist using
get_random_u32_below().

Additionally, ensure the error path correctly calculates the address range
to be reset if initialization fails, as the address increment logic has
been moved to a separate loop.

Link: https://lkml.kernel.org/r/20260120161510.3289089-1-pimyn@google.com


Fixes: 0ce20dd8 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: default avatarPimyn Girgis <pimyn@google.com>
Reviewed-by: default avatarAlexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Ernesto Martnez Garca <ernesto.martinezgarcia@tugraz.at>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Kees Cook <kees@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 412a32f0

mm/kfence/core.c

+19 −4
Original line number Diff line number Diff line
@@ -596,7 +596,7 @@ static void rcu_guarded_free(struct rcu_head *h) 
static unsigned long kfence_init_pool(void)

{

	unsigned long addr, start_pfn;

	int i;

	int i, rand;



	if (!arch_kfence_init_pool())

		return (unsigned long)__kfence_pool;
@@ -647,13 +647,27 @@ static unsigned long kfence_init_pool(void) 
		INIT_LIST_HEAD(&meta->list);

		raw_spin_lock_init(&meta->lock);

		meta->state = KFENCE_OBJECT_UNUSED;

		meta->addr = addr; /* Initialize for validation in metadata_to_pageaddr(). */

		list_add_tail(&meta->list, &kfence_freelist);

		/* Use addr to randomize the freelist. */

		meta->addr = i;



		/* Protect the right redzone. */

		if (unlikely(!kfence_protect(addr + PAGE_SIZE)))

		if (unlikely(!kfence_protect(addr + 2 * i * PAGE_SIZE + PAGE_SIZE)))

			goto reset_slab;

	}



	for (i = CONFIG_KFENCE_NUM_OBJECTS; i > 0; i--) {

		rand = get_random_u32_below(i);

		swap(kfence_metadata_init[i - 1].addr, kfence_metadata_init[rand].addr);

	}



	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {

		struct kfence_metadata *meta_1 = &kfence_metadata_init[i];

		struct kfence_metadata *meta_2 = &kfence_metadata_init[meta_1->addr];



		list_add_tail(&meta_2->list, &kfence_freelist);

	}

	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {

		kfence_metadata_init[i].addr = addr;

		addr += 2 * PAGE_SIZE;

	}
@@ -666,6 +680,7 @@ static unsigned long kfence_init_pool(void) 
	return 0;



reset_slab:

	addr += 2 * i * PAGE_SIZE;

	for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {

		struct page *page;