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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id i7sm11565112pgh.58.2020.08.07.10.16.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2020 10:16:27 -0700 (PDT) Date: Fri, 7 Aug 2020 10:16:26 -0700 From: Kees Cook To: Marco Elver Cc: Alexander Potapenko , Andrew Morton , David Rientjes , Joonsoo Kim , Pekka Enberg , Christoph Lameter , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: Odd-sized kmem_cache_alloc and slub_debug=Z Message-ID: <202008071010.69B612E@keescook> References: <20200807160627.GA1420741@elver.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200807160627.GA1420741@elver.google.com> X-Rspamd-Queue-Id: 03F6210053C30 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 07, 2020 at 06:06:27PM +0200, Marco Elver wrote: > I found that the below debug-code using kmem_cache_alloc(), when using > slub_debug=Z, results in the following crash: > > general protection fault, probably for non-canonical address 0xcccccca41caea170: 0000 [#1] PREEMPT SMP PTI > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.8.0+ #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014 > RIP: 0010:freelist_dereference mm/slub.c:272 [inline] > RIP: 0010:get_freepointer mm/slub.c:278 [inline] That really looks like more fun from my moving the freelist pointer... > R13: cccccca41caea160 R14: ffffe7c6a072ba80 R15: ffffa3a41c96d540 Except that it's all cccc at the start, which doesn't look like "data" nor the hardened freelist obfuscation. > FS: 0000000000000000(0000) GS:ffffa3a41fc00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: ffffa3a051c01000 CR3: 000000045140a001 CR4: 0000000000770ef0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > PKRU: 00000000 > Call Trace: > ___slab_alloc+0x336/0x340 mm/slub.c:2690 > __slab_alloc mm/slub.c:2714 [inline] > slab_alloc_node mm/slub.c:2788 [inline] > slab_alloc mm/slub.c:2832 [inline] > kmem_cache_alloc+0x135/0x200 mm/slub.c:2837 > start_kernel+0x3d6/0x44e init/main.c:1049 > secondary_startup_64+0xb6/0xc0 arch/x86/kernel/head_64.S:243 > > Any ideas what might be wrong? > > This does not crash when redzones are not enabled. > > Thanks, > -- Marco > > ------ >8 ------ > > diff --git a/init/main.c b/init/main.c > index 15bd0efff3df..f4aa5bb3f2ec 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -1041,6 +1041,16 @@ asmlinkage __visible void __init start_kernel(void) > sfi_init_late(); > kcsan_init(); > > + /* DEBUG CODE */ > + { > + struct kmem_cache *c = kmem_cache_create("test", 21, 1, 0, NULL); > + char *buf; > + BUG_ON(!c); > + buf = kmem_cache_alloc(c, GFP_KERNEL); > + kmem_cache_free(c, buf); > + kmem_cache_destroy(c); > + } > + > /* Do the rest non-__init'ed, we're now alive */ > arch_call_rest_init(); > Which kernel version? Can you send your CONFIG too? -- Kees Cook