Re: [PATCH 2/2] arm64: Clear the stack

From: Mark Rutland
Date: Thu Jul 19 2018 - 07:41:43 EST

On Wed, Jul 18, 2018 at 02:10:13PM -0700, Laura Abbott wrote:
>
> Implementation of stackleak based heavily on the x86 version
>
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> ---
> Since last time: Minor style cleanups. Re-wrote check_alloca to
> correctly handle all stack types. While doing that, I also realized
> current_top_of_stack was incorrect so I fixed that as well.
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/processor.h | 17 ++++++++++++++
> arch/arm64/kernel/entry.S | 7 ++++++
> arch/arm64/kernel/process.c | 32 +++++++++++++++++++++++++++
> arch/arm64/kvm/hyp/Makefile | 3 ++-
> drivers/firmware/efi/libstub/Makefile | 3 ++-
> include/linux/stackleak.h | 1 +
> 7 files changed, 62 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 42c090cf0292..216d36a49ab5 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -96,6 +96,7 @@ 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 a73ae1e49200..4f3062ee22c6 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -266,5 +266,22 @@ extern void __init minsigstksz_setup(void);
> #define SVE_SET_VL(arg) sve_set_current_vl(arg)
> #define SVE_GET_VL() sve_get_current_vl()
>
> +/*
> + * For CONFIG_STACKLEAK
> + *
> + * 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() \
> +({ \
> + unsigned long _low = 0; \
> + unsigned long _high = 0; \
> + \
> + current_stack_type(current, current_stack_pointer, &_low, &_high); \
> + _high; \
> +})

... with the info changes, this could be:

#define current_top_of_stack() \
({ \
struct stack_info _info; \
BUG_ON(!on_accessible_stack(current_stack_pinter, &_info)); \
_info->high; \
})

> +#define on_thread_stack() (on_task_stack(current, current_stack_pointer, NULL, NULL))

... and one fewer NULL here.

> +
> #endif /* __ASSEMBLY__ */
> #endif /* __ASM_PROCESSOR_H */
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 28ad8799406f..67d12016063d 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -431,6 +431,11 @@ tsk .req x28 // current thread_info
>
> .text
>
> + .macro stackleak_erase
> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
> + bl stackleak_erase
> +#endif
> + .endm
> /*
> * Exception vectors.
> */
> @@ -910,6 +915,7 @@ 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
> @@ -936,6 +942,7 @@ 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 e10bc363f533..904defa36689 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -493,3 +493,35 @@ void arch_setup_new_exec(void)
> {
> current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
> }
> +
> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
> +void __used stackleak_check_alloca(unsigned long size)
> +{
> + unsigned long stack_left;
> + enum stack_type type;
> + unsigned long current_sp = current_stack_pointer;
> + unsigned long low, high;
> +
> + type = current_stack_type(current, current_sp, &low, &high);
> + BUG_ON(type == STACK_TYPE_UNKNOWN);
> +
> + stack_left = current_sp - low;

... similarly with the info changes, this could be:

unsigned long current_sp = current_stack_pointer;
unsigned long stack_left;
struct stack_info info;

BUG_ON(!on_accessible_stack(current, current_sp, &info));

stack_lead = current_sp - info->low;

Otherwise, this looks good to me.

Thanks,
Mark.

> +
> + if (size >= stack_left) {
> + /*
> + * Kernel stack depth overflow is detected, let's report that.
> + * If CONFIG_VMAP_STACK is enabled, we can safely use BUG().
> + * If CONFIG_VMAP_STACK is disabled, BUG() handling can corrupt
> + * the neighbour memory. CONFIG_SCHED_STACK_END_CHECK calls
> + * panic() in a similar situation, so let's do the same if that
> + * option is on. Otherwise just use BUG() and hope for the best.
> + */
> +#if !defined(CONFIG_VMAP_STACK) && defined(CONFIG_SCHED_STACK_END_CHECK)
> + panic("alloca() over the kernel stack boundary\n");
> +#else
> + BUG();
> +#endif
> + }
> +}
> +EXPORT_SYMBOL(stackleak_check_alloca);
> +#endif
> 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 b911b973d328..08420ec6b7c3 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.
> --
> 2.17.1
>