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Fri, 07 Aug 2020 10:20:54 -0700 (PDT) Date: Fri, 7 Aug 2020 19:20:48 +0200 From: Marco Elver To: Kees Cook 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: <20200807172048.GB1467156@elver.google.com> References: <20200807160627.GA1420741@elver.google.com> <202008071010.69B612E@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202008071010.69B612E@keescook> User-Agent: Mutt/1.14.4 (2020-06-18) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 07, 2020 at 10:16AM -0700, Kees Cook wrote: > 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? Sorry, didn't see this before I replied to the other -- it's here: https://lkml.kernel.org/r/20200807171849.GA1467156@elver.google.com Thanks, -- Marco