From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A6148C433EF for ; Thu, 9 Jun 2022 12:17:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245313AbiFIMRd (ORCPT ); Thu, 9 Jun 2022 08:17:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41740 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237980AbiFIMR2 (ORCPT ); Thu, 9 Jun 2022 08:17:28 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90AFD305451 for ; Thu, 9 Jun 2022 05:17:23 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 38EE2B82D59 for ; Thu, 9 Jun 2022 12:17:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 160BCC34114; Thu, 9 Jun 2022 12:17:20 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="SBU4gzxG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1654777038; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=22Iuiuo76qv+0jlpTHCLD62sTQIyeIIPIjWm3iFwPNY=; b=SBU4gzxGLjm86tu6IhpPN6A2mxJHwBPDNxHvfJmB8KR9siYTWTdhgamlGEmURCj5NG0H0M /H/VAeROdJh9/vcJkptTg84PrLi2Ur985cOnyqOZDNwvC3D7jdNYGbUnW/xHMTeOnCpGZK 7V1I+MwcyuC5PR/mmHGP4RJiwX8ORjc= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 1ad02f64 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Thu, 9 Jun 2022 12:17:18 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: "Jason A. Donenfeld" , John Ogness , Alexander Potapenko , Marco Elver , Dmitry Vyukov , Geert Uytterhoeven Subject: [PATCH] mm/kfence: select random number before taking raw lock Date: Thu, 9 Jun 2022 14:17:09 +0200 Message-Id: <20220609121709.12939-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: John Ogness Cc: Alexander Potapenko Cc: Marco Elver Cc: Dmitry Vyukov Reported-by: Geert Uytterhoeven Signed-off-by: Jason A. Donenfeld --- mm/kfence/core.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 4e7cd4c8e687..6322b7729b50 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; + bool random_right_allocate = prandom_u32_max(2); + 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]); -- 2.35.1