From 327b18b7aaed5de3b548212e3ab75133bf323759 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 9 Jun 2022 14:33:19 +0200 Subject: mm/kfence: select random number before taking raw lock The RNG uses vanilla spinlocks, not raw spinlocks, so kfence should pick its random numbers before taking its raw spinlocks. This also has the nice effect of doing less work inside the lock. It should fix a splat that Geert saw with CONFIG_PROVE_RAW_LOCK_NESTING: dump_backtrace.part.0+0x98/0xc0 show_stack+0x14/0x28 dump_stack_lvl+0xac/0xec dump_stack+0x14/0x2c __lock_acquire+0x388/0x10a0 lock_acquire+0x190/0x2c0 _raw_spin_lock_irqsave+0x6c/0x94 crng_make_state+0x148/0x1e4 _get_random_bytes.part.0+0x4c/0xe8 get_random_u32+0x4c/0x140 __kfence_alloc+0x460/0x5c4 kmem_cache_alloc_trace+0x194/0x1dc __kthread_create_on_node+0x5c/0x1a8 kthread_create_on_node+0x58/0x7c printk_start_kthread.part.0+0x34/0xa8 printk_activate_kthreads+0x4c/0x54 do_one_initcall+0xec/0x278 kernel_init_freeable+0x11c/0x214 kernel_init+0x24/0x124 ret_from_fork+0x10/0x20 Link: https://lkml.kernel.org/r/20220609123319.17576-1-Jason@zx2c4.com Fixes: d4150779e60f ("random32: use real rng for non-deterministic randomness") Signed-off-by: Jason A. Donenfeld Reported-by: Geert Uytterhoeven Tested-by: Geert Uytterhoeven Reviewed-by: Marco Elver Reviewed-by: Petr Mladek Cc: John Ogness Cc: Alexander Potapenko Cc: Dmitry Vyukov Signed-off-by: Andrew Morton --- mm/kfence/core.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'mm/kfence') diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 4e7cd4c8e687..4b5e5a3d3a63 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -360,6 +360,9 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g unsigned long flags; struct slab *slab; void *addr; + const bool random_right_allocate = prandom_u32_max(2); + const bool random_fault = CONFIG_KFENCE_STRESS_TEST_FAULTS && + !prandom_u32_max(CONFIG_KFENCE_STRESS_TEST_FAULTS); /* Try to obtain a free object. */ raw_spin_lock_irqsave(&kfence_freelist_lock, flags); @@ -404,7 +407,7 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g * is that the out-of-bounds accesses detected are deterministic for * such allocations. */ - if (prandom_u32_max(2)) { + if (random_right_allocate) { /* Allocate on the "right" side, re-calculate address. */ meta->addr += PAGE_SIZE - size; meta->addr = ALIGN_DOWN(meta->addr, cache->align); @@ -444,7 +447,7 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g if (cache->ctor) cache->ctor(addr); - if (CONFIG_KFENCE_STRESS_TEST_FAULTS && !prandom_u32_max(CONFIG_KFENCE_STRESS_TEST_FAULTS)) + if (random_fault) kfence_protect(meta->addr); /* Random "faults" by protecting the object. */ atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]); -- cgit v1.2.3