Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752085AbdLCMXZ (ORCPT ); Sun, 3 Dec 2017 07:23:25 -0500 Received: from mail-pf0-f193.google.com ([209.85.192.193]:44870 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750994AbdLCMXW (ORCPT ); Sun, 3 Dec 2017 07:23:22 -0500 X-Google-Smtp-Source: AGs4zMaf417nISlodJ6a7yZcraOlFIrtI5iZNa9LQ+nrWP56c2ePJGvo6Gp3Rn7LcrYQCLfr2+lQwX3jMdi4Nz/O+mY= MIME-Version: 1.0 In-Reply-To: <20171201213643.2506-4-paullawrence@google.com> References: <20171201213643.2506-1-paullawrence@google.com> <20171201213643.2506-4-paullawrence@google.com> From: Dmitry Vyukov Date: Sun, 3 Dec 2017 13:23:00 +0100 Message-ID: Subject: Re: [PATCH v3 3/5] kasan: support alloca() poisoning To: Paul Lawrence Cc: Andrey Ryabinin , Alexander Potapenko , Masahiro Yamada , LKML , kasan-dev , Linux-MM , "open list:KERNEL BUILD + fi..." , Matthias Kaehlcke , Michael Davidson , Greg Hackmann 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: 4724 Lines: 120 On Fri, Dec 1, 2017 at 10:36 PM, Paul Lawrence 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 > Signed-off-by: Paul Lawrence > --- > mm/kasan/kasan.c | 34 ++++++++++++++++++++++++++++++++++ > mm/kasan/kasan.h | 8 ++++++++ > mm/kasan/report.c | 4 ++++ > scripts/Makefile.kasan | 3 ++- > 4 files changed, 48 insertions(+), 1 deletion(-) > > diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c > index 405bba487df5..d96b36088b2f 100644 > --- a/mm/kasan/kasan.c > +++ b/mm/kasan/kasan.c > @@ -736,6 +736,40 @@ 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) - > + rounded_up_size; > + size_t rounded_down_size = round_down(size, KASAN_SHADOW_SCALE_SIZE); > + > + const void *left_redzone = (const void *)(addr - > + KASAN_ALLOCA_REDZONE_SIZE); > + const void *right_redzone = (const void *)(addr + rounded_up_size); > + > + WARN_ON(!IS_ALIGNED(addr, KASAN_ALLOCA_REDZONE_SIZE)); > + > + kasan_unpoison_shadow((const void *)(addr + rounded_down_size), > + size - rounded_down_size); > + 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); > +} > +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) > +{ > + if (unlikely(!stack_top || stack_top > stack_bottom)) > + return; > + > + kasan_unpoison_shadow(stack_top, stack_bottom - stack_top); > +} > +EXPORT_SYMBOL(__asan_allocas_unpoison); > + > #ifdef CONFIG_MEMORY_HOTPLUG > static int __meminit 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 c70851a9a6a4..7c0bcd1f4c0d 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -24,6 +24,14 @@ > #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 410c8235e671..eff12e040498 100644 > --- a/mm/kasan/report.c > +++ b/mm/kasan/report.c > @@ -102,6 +102,10 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info) > case KASAN_USE_AFTER_SCOPE: > bug_type = "use-after-scope"; > break; > + case KASAN_ALLOCA_LEFT: > + case KASAN_ALLOCA_RIGHT: > + bug_type = "alloca-out-of-bounds"; > + break; > } > > return bug_type; > diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan > index 7c00be9216f4..b4983cf8a9d4 100644 > --- a/scripts/Makefile.kasan > +++ b/scripts/Makefile.kasan > @@ -32,7 +32,8 @@ else > $(call cc-param,asan-globals=1) \ > $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \ > $(call cc-param,asan-stack=1) \ > - $(call cc-param,asan-use-after-scope=1) > + $(call cc-param,asan-use-after-scope=1) \ > + $(call cc-param,asan-instrument-allocas=1) > endif > > endif Reviewed-by: Dmitry Vyukov