From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751633AbeEBVb0 (ORCPT ); Wed, 2 May 2018 17:31:26 -0400 Received: from mail-ua0-f194.google.com ([209.85.217.194]:34721 "EHLO mail-ua0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750970AbeEBVbT (ORCPT ); Wed, 2 May 2018 17:31:19 -0400 X-Google-Smtp-Source: AB8JxZqd7k2GxW331o8QDAzLTz2oyVOweX2orB71tOQHVXcvE/3JQoiwFjejG1RfKWZbkMIrY2EQqmb2XNJYkLImIfc= MIME-Version: 1.0 In-Reply-To: <20180502203326.9491-3-labbott@redhat.com> References: <20180502203326.9491-1-labbott@redhat.com> <20180502203326.9491-3-labbott@redhat.com> From: Kees Cook Date: Wed, 2 May 2018 14:31:16 -0700 X-Google-Sender-Auth: gxOoiHBonHFXkTN62GcLzshS03I Message-ID: Subject: Re: [PATCH 2/2] arm64: Clear the stack To: Laura Abbott Cc: Alexander Popov , Mark Rutland , Ard Biesheuvel , Kernel Hardening , linux-arm-kernel , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 2, 2018 at 1:33 PM, Laura Abbott wrote: > > Implementation of stackleak based heavily on the x86 version Awesome! Notes below for both you and Alexander, since I think we can create a common code base instead of having near-duplicates in the arch/ trees... > > Signed-off-by: Laura Abbott > --- > Now written in C instead of a bunch of assembly. > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/processor.h | 6 ++++ > arch/arm64/kernel/Makefile | 3 ++ > arch/arm64/kernel/entry.S | 6 ++++ > arch/arm64/kernel/erase.c | 55 +++++++++++++++++++++++++++++++++++ > arch/arm64/kernel/process.c | 16 ++++++++++ > drivers/firmware/efi/libstub/Makefile | 3 +- > scripts/Makefile.gcc-plugins | 5 +++- > 8 files changed, 93 insertions(+), 2 deletions(-) > create mode 100644 arch/arm64/kernel/erase.c > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index eb2cf4938f6d..b0221db95dc9 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -92,6 +92,7 @@ config ARM64 > select HAVE_ARCH_MMAP_RND_BITS > select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT > select HAVE_ARCH_SECCOMP_FILTER > + select HAVE_ARCH_STACKLEAK > select HAVE_ARCH_THREAD_STRUCT_WHITELIST > select HAVE_ARCH_TRACEHOOK > select HAVE_ARCH_TRANSPARENT_HUGEPAGE > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 767598932549..d31ab80ff647 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -124,6 +124,12 @@ struct thread_struct { > unsigned long fault_address; /* fault info */ > unsigned long fault_code; /* ESR_EL1 value */ > struct debug_info debug; /* debugging */ > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + unsigned long lowest_stack; > +#ifdef CONFIG_STACKLEAK_METRICS > + unsigned long prev_lowest_stack; > +#endif > +#endif I wonder if x86 and arm64 could include a common struct here that was empty when the plugin is disabled... it would keep the ifdefs in one place. Maybe include/linux/stackleak.h could be: ---start--- /* Poison value points to the unused hole in the virtual memory map */ #define STACKLEAK_POISON -0xBEEF #define STACKLEAK_POISON_CHECK_DEPTH 128 struct stackleak { #ifdef CONFIG_GCC_PLUGIN_STACKLEAK unsigned long lowest; #ifdef CONFIG_STACKLEAK_METRICS unsigned long prev_lowest; #endif #endif }; asmlinkage void erase_kstack(void); ---eof--- and arch/*/include/asm/processor.h could do: @@ -124,6 +124,12 @@ struct thread_struct { unsigned long fault_address; /* fault info */ unsigned long fault_code; /* ESR_EL1 value */ struct debug_info debug; /* debugging */ + struct stackleak stackleak; and arch/x86/entry/erase.c could move to maybe kernel/stackleak.c? (Oh, I notice this needs an SPDX line too.) > static inline void arch_thread_struct_whitelist(unsigned long *offset, > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index bf825f38d206..0ceea613c65b 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -55,6 +55,9 @@ arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o > arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o > arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o > > +arm64-obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += erase.o > +KASAN_SANITIZE_erase.o := n > + > obj-y += $(arm64-obj-y) vdso/ probes/ > obj-m += $(arm64-obj-m) > head-y := head.o > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index ec2ee720e33e..3144f1ebdc18 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -401,6 +401,11 @@ tsk .req x28 // current thread_info > > .text > > + .macro ERASE_KSTACK > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + bl erase_kstack > +#endif > + .endm > /* > * Exception vectors. > */ > @@ -906,6 +911,7 @@ ret_to_user: > cbnz x2, work_pending > finish_ret_to_user: > enable_step_tsk x1, x2 > + ERASE_KSTACK > kernel_exit 0 > ENDPROC(ret_to_user) Nice. All of the return paths end up here (I went looking for ret_from_fork's path). :) > > diff --git a/arch/arm64/kernel/erase.c b/arch/arm64/kernel/erase.c > new file mode 100644 > index 000000000000..b8b5648d893b > --- /dev/null > +++ b/arch/arm64/kernel/erase.c > @@ -0,0 +1,55 @@ > +#include > +#include > +#include > +#include > +#include > + > +asmlinkage void erase_kstack(void) > +{ > + unsigned long p = current->thread.lowest_stack; > + unsigned long boundary = p & ~(THREAD_SIZE - 1); > + unsigned long poison = 0; > + const unsigned long check_depth = STACKLEAK_POISON_CHECK_DEPTH / > + sizeof(unsigned long); > + > + /* > + * Let's search for the poison value in the stack. > + * Start from the lowest_stack and go to the bottom. > + */ > + while (p > boundary && poison <= check_depth) { > + if (*(unsigned long *)p == STACKLEAK_POISON) > + poison++; > + else > + poison = 0; > + > + p -= sizeof(unsigned long); > + } > + > + /* > + * One long int at the bottom of the thread stack is reserved and > + * should not be poisoned (see CONFIG_SCHED_STACK_END_CHECK). > + */ > + if (p == boundary) > + p += sizeof(unsigned long); > + > +#ifdef CONFIG_STACKLEAK_METRICS > + current->thread.prev_lowest_stack = p; > +#endif > + > + /* > + * So let's write the poison value to the kernel stack. > + * Start from the address in p and move up till the new boundary. > + */ > + boundary = current_stack_pointer; This is the only difference between x86 and arm64 in this code. What do you think about implementing on_thread_stack() to match x86: if (on_thread_stack()) boundary = current_stack_pointer; else boundary = current_top_of_stack(); then we could make this common code too instead of having two copies in arch/? > + BUG_ON(boundary - p >= THREAD_SIZE); > + > + while (p < boundary) { > + *(unsigned long *)p = STACKLEAK_POISON; > + p += sizeof(unsigned long); > + } > + > + /* Reset the lowest_stack value for the next syscall */ > + current->thread.lowest_stack = current_stack_pointer; > +} > + > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index f08a2ed9db0d..156fa0a0da19 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -364,6 +364,9 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > p->thread.cpu_context.pc = (unsigned long)ret_from_fork; > p->thread.cpu_context.sp = (unsigned long)childregs; > > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + p->thread.lowest_stack = (unsigned long)task_stack_page(p); > +#endif > ptrace_hw_copy_thread(p); > > return 0; > @@ -493,3 +496,16 @@ void arch_setup_new_exec(void) > { > current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0; > } > + > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > +void __used check_alloca(unsigned long size) > +{ > + unsigned long sp, stack_left; > + > + sp = current_stack_pointer; > + > + stack_left = sp & (THREAD_SIZE - 1); > + BUG_ON(stack_left < 256 || size >= stack_left - 256); > +} > +EXPORT_SYMBOL(check_alloca); This is pretty different from x86. Is this just an artifact of ORC, or something else? > +#endif > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile > index a34e9290a699..25dd2a14560d 100644 > --- a/drivers/firmware/efi/libstub/Makefile > +++ b/drivers/firmware/efi/libstub/Makefile > @@ -20,7 +20,8 @@ cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt > KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \ > -D__NO_FORTIFY \ > $(call cc-option,-ffreestanding) \ > - $(call cc-option,-fno-stack-protector) > + $(call cc-option,-fno-stack-protector) \ > + $(DISABLE_STACKLEAK_PLUGIN) > > GCOV_PROFILE := n > KASAN_SANITIZE := n > diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins > index 8d6070fc538f..6cc0e35d3324 100644 > --- a/scripts/Makefile.gcc-plugins > +++ b/scripts/Makefile.gcc-plugins > @@ -37,11 +37,14 @@ ifdef CONFIG_GCC_PLUGINS > > gcc-plugin-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak_plugin.so > gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STACKLEAK) += -DSTACKLEAK_PLUGIN -fplugin-arg-stackleak_plugin-track-min-size=$(CONFIG_STACKLEAK_TRACK_MIN_SIZE) > + ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + DISABLE_STACKLEAK_PLUGIN += -fplugin-arg-stackleak_plugin-disable > + endif > > GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y)) > > export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR > - export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN > + export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN DISABLE_STACKLEAK_PLUGIN > > ifneq ($(PLUGINCC),) > # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication. > -- > 2.14.3 > -Kees -- Kees Cook Pixel Security From mboxrd@z Thu Jan 1 00:00:00 1970 From: keescook@chromium.org (Kees Cook) Date: Wed, 2 May 2018 14:31:16 -0700 Subject: [PATCH 2/2] arm64: Clear the stack In-Reply-To: <20180502203326.9491-3-labbott@redhat.com> References: <20180502203326.9491-1-labbott@redhat.com> <20180502203326.9491-3-labbott@redhat.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, May 2, 2018 at 1:33 PM, Laura Abbott wrote: > > Implementation of stackleak based heavily on the x86 version Awesome! Notes below for both you and Alexander, since I think we can create a common code base instead of having near-duplicates in the arch/ trees... > > Signed-off-by: Laura Abbott > --- > Now written in C instead of a bunch of assembly. > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/processor.h | 6 ++++ > arch/arm64/kernel/Makefile | 3 ++ > arch/arm64/kernel/entry.S | 6 ++++ > arch/arm64/kernel/erase.c | 55 +++++++++++++++++++++++++++++++++++ > arch/arm64/kernel/process.c | 16 ++++++++++ > drivers/firmware/efi/libstub/Makefile | 3 +- > scripts/Makefile.gcc-plugins | 5 +++- > 8 files changed, 93 insertions(+), 2 deletions(-) > create mode 100644 arch/arm64/kernel/erase.c > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index eb2cf4938f6d..b0221db95dc9 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -92,6 +92,7 @@ config ARM64 > select HAVE_ARCH_MMAP_RND_BITS > select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT > select HAVE_ARCH_SECCOMP_FILTER > + select HAVE_ARCH_STACKLEAK > select HAVE_ARCH_THREAD_STRUCT_WHITELIST > select HAVE_ARCH_TRACEHOOK > select HAVE_ARCH_TRANSPARENT_HUGEPAGE > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 767598932549..d31ab80ff647 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -124,6 +124,12 @@ struct thread_struct { > unsigned long fault_address; /* fault info */ > unsigned long fault_code; /* ESR_EL1 value */ > struct debug_info debug; /* debugging */ > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + unsigned long lowest_stack; > +#ifdef CONFIG_STACKLEAK_METRICS > + unsigned long prev_lowest_stack; > +#endif > +#endif I wonder if x86 and arm64 could include a common struct here that was empty when the plugin is disabled... it would keep the ifdefs in one place. Maybe include/linux/stackleak.h could be: ---start--- /* Poison value points to the unused hole in the virtual memory map */ #define STACKLEAK_POISON -0xBEEF #define STACKLEAK_POISON_CHECK_DEPTH 128 struct stackleak { #ifdef CONFIG_GCC_PLUGIN_STACKLEAK unsigned long lowest; #ifdef CONFIG_STACKLEAK_METRICS unsigned long prev_lowest; #endif #endif }; asmlinkage void erase_kstack(void); ---eof--- and arch/*/include/asm/processor.h could do: @@ -124,6 +124,12 @@ struct thread_struct { unsigned long fault_address; /* fault info */ unsigned long fault_code; /* ESR_EL1 value */ struct debug_info debug; /* debugging */ + struct stackleak stackleak; and arch/x86/entry/erase.c could move to maybe kernel/stackleak.c? (Oh, I notice this needs an SPDX line too.) > static inline void arch_thread_struct_whitelist(unsigned long *offset, > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index bf825f38d206..0ceea613c65b 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -55,6 +55,9 @@ arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o > arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o > arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o > > +arm64-obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += erase.o > +KASAN_SANITIZE_erase.o := n > + > obj-y += $(arm64-obj-y) vdso/ probes/ > obj-m += $(arm64-obj-m) > head-y := head.o > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index ec2ee720e33e..3144f1ebdc18 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -401,6 +401,11 @@ tsk .req x28 // current thread_info > > .text > > + .macro ERASE_KSTACK > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + bl erase_kstack > +#endif > + .endm > /* > * Exception vectors. > */ > @@ -906,6 +911,7 @@ ret_to_user: > cbnz x2, work_pending > finish_ret_to_user: > enable_step_tsk x1, x2 > + ERASE_KSTACK > kernel_exit 0 > ENDPROC(ret_to_user) Nice. All of the return paths end up here (I went looking for ret_from_fork's path). :) > > diff --git a/arch/arm64/kernel/erase.c b/arch/arm64/kernel/erase.c > new file mode 100644 > index 000000000000..b8b5648d893b > --- /dev/null > +++ b/arch/arm64/kernel/erase.c > @@ -0,0 +1,55 @@ > +#include > +#include > +#include > +#include > +#include > + > +asmlinkage void erase_kstack(void) > +{ > + unsigned long p = current->thread.lowest_stack; > + unsigned long boundary = p & ~(THREAD_SIZE - 1); > + unsigned long poison = 0; > + const unsigned long check_depth = STACKLEAK_POISON_CHECK_DEPTH / > + sizeof(unsigned long); > + > + /* > + * Let's search for the poison value in the stack. > + * Start from the lowest_stack and go to the bottom. > + */ > + while (p > boundary && poison <= check_depth) { > + if (*(unsigned long *)p == STACKLEAK_POISON) > + poison++; > + else > + poison = 0; > + > + p -= sizeof(unsigned long); > + } > + > + /* > + * One long int at the bottom of the thread stack is reserved and > + * should not be poisoned (see CONFIG_SCHED_STACK_END_CHECK). > + */ > + if (p == boundary) > + p += sizeof(unsigned long); > + > +#ifdef CONFIG_STACKLEAK_METRICS > + current->thread.prev_lowest_stack = p; > +#endif > + > + /* > + * So let's write the poison value to the kernel stack. > + * Start from the address in p and move up till the new boundary. > + */ > + boundary = current_stack_pointer; This is the only difference between x86 and arm64 in this code. What do you think about implementing on_thread_stack() to match x86: if (on_thread_stack()) boundary = current_stack_pointer; else boundary = current_top_of_stack(); then we could make this common code too instead of having two copies in arch/? > + BUG_ON(boundary - p >= THREAD_SIZE); > + > + while (p < boundary) { > + *(unsigned long *)p = STACKLEAK_POISON; > + p += sizeof(unsigned long); > + } > + > + /* Reset the lowest_stack value for the next syscall */ > + current->thread.lowest_stack = current_stack_pointer; > +} > + > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index f08a2ed9db0d..156fa0a0da19 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -364,6 +364,9 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > p->thread.cpu_context.pc = (unsigned long)ret_from_fork; > p->thread.cpu_context.sp = (unsigned long)childregs; > > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + p->thread.lowest_stack = (unsigned long)task_stack_page(p); > +#endif > ptrace_hw_copy_thread(p); > > return 0; > @@ -493,3 +496,16 @@ void arch_setup_new_exec(void) > { > current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0; > } > + > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > +void __used check_alloca(unsigned long size) > +{ > + unsigned long sp, stack_left; > + > + sp = current_stack_pointer; > + > + stack_left = sp & (THREAD_SIZE - 1); > + BUG_ON(stack_left < 256 || size >= stack_left - 256); > +} > +EXPORT_SYMBOL(check_alloca); This is pretty different from x86. Is this just an artifact of ORC, or something else? > +#endif > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile > index a34e9290a699..25dd2a14560d 100644 > --- a/drivers/firmware/efi/libstub/Makefile > +++ b/drivers/firmware/efi/libstub/Makefile > @@ -20,7 +20,8 @@ cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt > KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \ > -D__NO_FORTIFY \ > $(call cc-option,-ffreestanding) \ > - $(call cc-option,-fno-stack-protector) > + $(call cc-option,-fno-stack-protector) \ > + $(DISABLE_STACKLEAK_PLUGIN) > > GCOV_PROFILE := n > KASAN_SANITIZE := n > diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins > index 8d6070fc538f..6cc0e35d3324 100644 > --- a/scripts/Makefile.gcc-plugins > +++ b/scripts/Makefile.gcc-plugins > @@ -37,11 +37,14 @@ ifdef CONFIG_GCC_PLUGINS > > gcc-plugin-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak_plugin.so > gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STACKLEAK) += -DSTACKLEAK_PLUGIN -fplugin-arg-stackleak_plugin-track-min-size=$(CONFIG_STACKLEAK_TRACK_MIN_SIZE) > + ifdef CONFIG_GCC_PLUGIN_STACKLEAK > + DISABLE_STACKLEAK_PLUGIN += -fplugin-arg-stackleak_plugin-disable > + endif > > GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y)) > > export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR > - export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN > + export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN DISABLE_STACKLEAK_PLUGIN > > ifneq ($(PLUGINCC),) > # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication. > -- > 2.14.3 > -Kees -- Kees Cook Pixel Security