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Date: Mon, 2 Jul 2018 11:48:05 -0700
From: Laura Abbott <labbott@...hat.com>
To: alex.popov@...ux.com, Kees Cook <keescook@...omium.org>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: kernel-hardening@...ts.openwall.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: Clear the stack
On 07/02/2018 06:02 AM, Alexander Popov wrote:
> Hello Laura,
>
> Thanks for your work!
> Please see my comments below.
>
> On 29.06.2018 22:05, Laura Abbott wrote:
>> Implementation of stackleak based heavily on the x86 version
>>
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>> Changes since last time:
>> - Minor name change in entry.S
>> - Converted to use the generic interfaces so there's minimal additions.
>> - Added the fast syscall path.
>> - Addition of on_thread_stack and current_top_of_stack
>> - Disable stackleak on hyp per suggestion
>> - Added a define for check_alloca. I'm still not sure about keeping it
>> since the x86 version got reworked?
>>
>> I've mostly kept this as one patch with a minimal commit text. I can
>> split it up and elaborate more before final merging.
>> ---
>> arch/arm64/Kconfig | 1 +
>> arch/arm64/include/asm/processor.h | 9 +++++++++
>> arch/arm64/kernel/entry.S | 7 +++++++
>> arch/arm64/kernel/process.c | 16 ++++++++++++++++
>> arch/arm64/kvm/hyp/Makefile | 3 ++-
>> drivers/firmware/efi/libstub/Makefile | 3 ++-
>> include/linux/stackleak.h | 1 +
>> scripts/Makefile.gcc-plugins | 5 ++++-
>> 8 files changed, 42 insertions(+), 3 deletions(-)
>>
>> 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..73914fd7e142 100644
>> --- a/arch/arm64/include/asm/processor.h
>> +++ b/arch/arm64/include/asm/processor.h
>> @@ -248,5 +248,14 @@ void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused);
>> #define SVE_SET_VL(arg) sve_set_current_vl(arg)
>> #define SVE_GET_VL() sve_get_current_vl()
>>
>> +/*
>> + * For stackleak
>
> May I ask you to call it STACKLEAK here and in other places for easier grep?
>
Sure
>> + *
>> + * These need to be macros because otherwise we get stuck in a nightmare
>> + * of header definitions for the use of task_stack_page.
>> + */
>> +#define current_top_of_stack() (task_stack_page(current) + THREAD_SIZE)
>> +#define on_thread_stack() (on_task_stack(current, current_stack_pointer))
>> +
>> #endif /* __ASSEMBLY__ */
>> #endif /* __ASM_PROCESSOR_H */
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index ec2ee720e33e..31c9da7d401e 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 stackleak_erase
>
> Could you rename the macro to STACKLEAK_ERASE for similarity with x86?
>
Mark Rutland had previously asked for this to be lowercase.
I really don't care one way or the other so I'll defer to
someone else to have the final word.
>> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>> + bl stackleak_erase_kstack
>> +#endif
>> + .endm
>> /*
>> * Exception vectors.
>> */
>> @@ -880,6 +885,7 @@ ret_fast_syscall:
>> and x2, x1, #_TIF_WORK_MASK
>> cbnz x2, work_pending
>> enable_step_tsk x1, x2
>> + stackleak_erase
>> kernel_exit 0
>> ret_fast_syscall_trace:
>> enable_daif
>> @@ -906,6 +912,7 @@ ret_to_user:
>> cbnz x2, work_pending
>> finish_ret_to_user:
>> enable_step_tsk x1, x2
>> + stackleak_erase
>> kernel_exit 0
>> ENDPROC(ret_to_user)
>>
>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>> index f08a2ed9db0d..9f0f135f8b66 100644
>> --- a/arch/arm64/kernel/process.c
>> +++ b/arch/arm64/kernel/process.c
>> @@ -493,3 +493,19 @@ void arch_setup_new_exec(void)
>> {
>> current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
>> }
>> +
>> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>> +#define MIN_STACK_LEFT 256
>> +
>> +void __used stackleak_check_alloca(unsigned long size)
>> +{
>> + unsigned long sp, stack_left;
>> +
>> + sp = current_stack_pointer;
>> +
>> + stack_left = sp & (THREAD_SIZE - 1);
>> + BUG_ON(stack_left < MIN_STACK_LEFT ||
>> + size >= stack_left - MIN_STACK_LEFT);
>> +}
>> +EXPORT_SYMBOL(stackleak_check_alloca);
>> +#endif
>
> This code should be updated.
> You may remember the troubles I had with MIN_STACK_LEFT:
> http://openwall.com/lists/kernel-hardening/2018/05/11/12
> Please see that thread where Mark Rutland and I worked out the solution.
>
Ah yeah, I missed the details in that thread. Thanks for
that pointer.
> By the way, different stacks on x86_64 have different sizes. Is it false for arm64?
>
Currently everything except the overflow stack looks to be
the same size but there's also another stack I missed. It might
be cleaner just to use on_accessible_stack and then another
function to get the top of stack. This also might just be
reimplementing what x86 already has? (Mark, Ard?)
Thanks,
Laura
>> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
>> index 4313f7475333..2fabc2dc1966 100644
>> --- a/arch/arm64/kvm/hyp/Makefile
>> +++ b/arch/arm64/kvm/hyp/Makefile
>> @@ -3,7 +3,8 @@
>> # Makefile for Kernel-based Virtual Machine module, HYP part
>> #
>>
>> -ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
>> +ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING \
>> + $(DISABLE_STACKLEAK_PLUGIN)
>>
>> KVM=../../../../virt/kvm
>>
>> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
>> index a34e9290a699..25dd2a14560d 100644
>> --- a/drivers/firmware/efi/libstub/Makefile
>> +++ b/drivers/firmware/efi/libstub/Makefile
>> @@ -20,7 +20,8 @@ cflags-$(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) \
>> + $(DISABLE_STACKLEAK_PLUGIN)
>>
>> GCOV_PROFILE := n
>> KASAN_SANITIZE := n
>> diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
>> index e2da99b3a191..00d62b302efb 100644
>> --- a/include/linux/stackleak.h
>> +++ b/include/linux/stackleak.h
>> @@ -5,6 +5,7 @@
>> #include <linux/sched.h>
>> #include <linux/sched/task_stack.h>
>>
>> +#include <asm/stacktrace.h>
>> /*
>> * Check that the poison value points to the unused hole in the
>> * virtual memory map for your platform.
>> diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
>> index a535742a1c06..972ce4ca7f6a 100644
>> --- a/scripts/Makefile.gcc-plugins
>> +++ b/scripts/Makefile.gcc-plugins
>> @@ -37,11 +37,14 @@ ifdef CONFIG_GCC_PLUGINS
>>
>> gcc-plugin-$(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.
>>
>
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