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Date: Mon, 2 Jul 2018 16:02:01 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Laura Abbott <labbott@...hat.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
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?
> + *
> + * 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?
> +#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.
By the way, different stacks on x86_64 have different sizes. Is it false for arm64?
> 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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