Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753791AbdGJIos (ORCPT ); Mon, 10 Jul 2017 04:44:48 -0400 Received: from mail-oi0-f41.google.com ([209.85.218.41]:33893 "EHLO mail-oi0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753770AbdGJIor (ORCPT ); Mon, 10 Jul 2017 04:44:47 -0400 MIME-Version: 1.0 In-Reply-To: <20170706220114.142438-2-ghackmann@google.com> References: <20170706220114.142438-1-ghackmann@google.com> <20170706220114.142438-2-ghackmann@google.com> From: Dmitry Vyukov Date: Mon, 10 Jul 2017 10:44:15 +0200 Message-ID: Subject: Re: [PATCH 1/4] kasan: support alloca() poisoning To: Greg Hackmann Cc: Andrey Ryabinin , Alexander Potapenko , Masahiro Yamada , Michal Marek , LKML , kasan-dev , "linux-mm@kvack.org" , "open list:KERNEL BUILD + fi..." , Matthias Kaehlcke , Michael Davidson Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5255 Lines: 147 On Fri, Jul 7, 2017 at 12:01 AM, Greg Hackmann wrote: > clang's AddressSanitizer implementation adds redzones on either side of > alloca()ed buffers. These redzones are 32-byte aligned and at least 32 > bytes long. > > __asan_alloca_poison() is passed the size and address of the allocated > buffer, *excluding* the redzones on either side. The left redzone will > always be to the immediate left of this buffer; but AddressSanitizer may > need to add padding between the end of the buffer and the right redzone. > If there are any 8-byte chunks inside this padding, we should poison > those too. > > __asan_allocas_unpoison() is just passed the top and bottom of the > dynamic stack area, so unpoisoning is simpler. > > Signed-off-by: Greg Hackmann > --- > lib/test_kasan.c | 22 ++++++++++++++++++++++ > mm/kasan/kasan.c | 26 ++++++++++++++++++++++++++ > mm/kasan/kasan.h | 8 ++++++++ > mm/kasan/report.c | 3 +++ > 4 files changed, 59 insertions(+) > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c > index a25c9763fce1..f774fcafb696 100644 > --- a/lib/test_kasan.c > +++ b/lib/test_kasan.c > @@ -473,6 +473,26 @@ static noinline void __init use_after_scope_test(void) > p[1023] = 1; > } > > +static noinline void __init kasan_alloca_oob_left(void) > +{ > + volatile int i = 10; > + char alloca_array[i]; > + char *p = alloca_array - 1; > + > + pr_info("out-of-bounds to left on alloca\n"); > + *(volatile char *)p; > +} > + > +static noinline void __init kasan_alloca_oob_right(void) > +{ > + volatile int i = 10; > + char alloca_array[i]; > + char *p = alloca_array + round_up(i, 8); > + > + pr_info("out-of-bounds to right on alloca\n"); > + *(volatile char *)p; > +} > + > static int __init kmalloc_tests_init(void) > { > /* > @@ -503,6 +523,8 @@ static int __init kmalloc_tests_init(void) > memcg_accounted_kmem_cache(); > kasan_stack_oob(); > kasan_global_oob(); > + kasan_alloca_oob_left(); > + kasan_alloca_oob_right(); > ksize_unpoisons_memory(); > copy_user_test(); > use_after_scope_test(); > diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c > index c81549d5c833..892b626f564b 100644 > --- a/mm/kasan/kasan.c > +++ b/mm/kasan/kasan.c > @@ -802,6 +802,32 @@ void __asan_unpoison_stack_memory(const void *addr, size_t size) > } > EXPORT_SYMBOL(__asan_unpoison_stack_memory); > > +/* Emitted by compiler to poison alloca()ed objects. */ > +void __asan_alloca_poison(unsigned long addr, size_t size) > +{ > + size_t rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE); > + size_t padding_size = round_up(size, KASAN_ALLOCA_REDZONE_SIZE) - > + round_up(size, KASAN_SHADOW_SCALE_SIZE); Perhaps s/round_up(size, KASAN_SHADOW_SCALE_SIZE)/rounded_up_size/ because we already calculated that. > + > + const void *left_redzone = (const void *)(addr - > + KASAN_ALLOCA_REDZONE_SIZE); > + const void *right_redzone = (const void *)(addr + rounded_up_size); Please check that size is rounded to KASAN_ALLOCA_REDZONE_SIZE. That's the expectation, right? That can change is clang silently. > + kasan_poison_shadow(left_redzone, KASAN_ALLOCA_REDZONE_SIZE, > + KASAN_ALLOCA_LEFT); > + kasan_poison_shadow(right_redzone, > + padding_size + KASAN_ALLOCA_REDZONE_SIZE, > + KASAN_ALLOCA_RIGHT); We also need to poison the unaligned part at the end of the object from size to rounded_up_size. You can see how we do it for heap objects. > +} > +EXPORT_SYMBOL(__asan_alloca_poison); > +/* Emitted by compiler to unpoison alloca()ed areas when the stack unwinds. */ > +void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom) > +{ > + kasan_unpoison_shadow(stack_top, stack_bottom - stack_top); > +} > +EXPORT_SYMBOL(__asan_allocas_unpoison); > + > #ifdef CONFIG_MEMORY_HOTPLUG > static int kasan_mem_notifier(struct notifier_block *nb, > unsigned long action, void *data) > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > index 1229298cce64..b857dc70d6a2 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -23,6 +23,14 @@ > #define KASAN_STACK_PARTIAL 0xF4 > #define KASAN_USE_AFTER_SCOPE 0xF8 > > +/* > + * alloca redzone shadow values > + */ > +#define KASAN_ALLOCA_LEFT 0xCA > +#define KASAN_ALLOCA_RIGHT 0xCB > + > +#define KASAN_ALLOCA_REDZONE_SIZE 32 > + > /* Don't break randconfig/all*config builds */ > #ifndef KASAN_ABI_VERSION > #define KASAN_ABI_VERSION 1 > diff --git a/mm/kasan/report.c b/mm/kasan/report.c > index beee0e980e2d..c6a5b7ab9e3a 100644 > --- a/mm/kasan/report.c > +++ b/mm/kasan/report.c > @@ -101,6 +101,9 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info) > break; > case KASAN_USE_AFTER_SCOPE: > bug_type = "use-after-scope"; > + case KASAN_ALLOCA_LEFT: > + case KASAN_ALLOCA_RIGHT: > + bug_type = "alloca-out-of-bounds"; > break; > } > > -- > 2.13.2.725.g09c95d1e9-goog >