Re: [PATCH] arch/riscv: Add support for STACKLEAK gcc plugin

[Kees Cook <keescook@chromium.org>]

On Wed, Jun 15, 2022 at 02:38:29PM -0700, Dao Lu wrote:
> This adds support for STACKLEAK gcc plugin to ricv by implementing

typo: riscv

> stackleak_check_alloca, based heavily on the arm64 version, and adding

stackleak_check_alloca does not exist. Was this maybe from an older
commit log?

> the two helpers used by the stackleak common code:
> current_top_of_stack() and on_thread_stack(). This also adds the missing
> helper functions for riscv, on_stack() and on_task_stack().
> Additionally, this disables the plugin for EFI stub code for riscv.

I can't speak to the arch-specific bits here, but if this passes the
current LKDTM tests, then that should be a good indication that it's
working. :)

> 
> Signed-off-by: Dao Lu <daolu@rivosinc.com>
> ---
>  arch/riscv/Kconfig                    |  1 +
>  arch/riscv/include/asm/processor.h    | 18 ++++++++++++++++++
>  arch/riscv/include/asm/stacktrace.h   | 27 +++++++++++++++++++++++++++
>  arch/riscv/kernel/entry.S             |  3 +++
>  drivers/firmware/efi/libstub/Makefile |  2 +-
>  5 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index c22f58155948..22aa146acd25 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -80,6 +80,7 @@ config RISCV
>  	select HAVE_ARCH_MMAP_RND_BITS if MMU
>  	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>  	select HAVE_ARCH_SECCOMP_FILTER
> +	select HAVE_ARCH_STACKLEAK
>  	select HAVE_ARCH_TRACEHOOK
>  	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
>  	select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index 21c8072dce17..3a7505ab7f58 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -85,6 +85,24 @@ int riscv_of_parent_hartid(struct device_node *node);
>  extern void riscv_fill_hwcap(void);
>  extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
>  
> +/*
> + * For CONFIG_GCC_PLUGIN_STACKLEAK
> + *
> + * These need to be macros because otherwise we get stuck in a nightmare
> + * of header definitions for the use of task_stack_page.
> + */
> +
> +struct stack_info {
> +	unsigned long low;
> +	unsigned long high;
> +};
> +
> +/*
> + * The top of the current task's task stack
> + */
> +#define current_top_of_stack()	((unsigned long)current->stack + THREAD_SIZE)
> +#define on_thread_stack()	(on_task_stack(current, current_stack_pointer, 1, NULL))
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_RISCV_PROCESSOR_H */
> diff --git a/arch/riscv/include/asm/stacktrace.h b/arch/riscv/include/asm/stacktrace.h
> index 3450c1912afd..afb66b677b6a 100644
> --- a/arch/riscv/include/asm/stacktrace.h
> +++ b/arch/riscv/include/asm/stacktrace.h
> @@ -16,4 +16,31 @@ extern void notrace walk_stackframe(struct task_struct *task, struct pt_regs *re
>  extern void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
>  			   const char *loglvl);
>  
> +static inline bool on_stack(unsigned long sp, unsigned long size,
> +			    unsigned long low, unsigned long high,
> +			    struct stack_info *info)
> +{
> +	if (!low)
> +		return false;
> +
> +	if (sp < low || sp + size < sp || sp + size > high)
> +		return false;
> +
> +	if (info) {
> +		info->low = low;
> +		info->high = high;
> +	}
> +	return true;
> +}
> +
> +static inline bool on_task_stack(const struct task_struct *tsk,
> +				 unsigned long sp, unsigned long size,
> +				 struct stack_info *info)
> +{
> +	unsigned long low = (unsigned long)task_stack_page(tsk);
> +	unsigned long high = low + THREAD_SIZE;
> +
> +	return on_stack(sp, size, low, high, info);
> +}
> +
>  #endif /* _ASM_RISCV_STACKTRACE_H */
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 2e5b88ca11ce..65d441cb560f 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -264,6 +264,9 @@ ret_from_exception:
>  	bnez s0, resume_kernel
>  
>  resume_userspace:
> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
> +	call stackleak_erase
> +#endif
>  	/* Interrupts must be disabled here so flags are checked atomically */
>  	REG_L s0, TASK_TI_FLAGS(tp) /* current_thread_info->flags */
>  	andi s1, s0, _TIF_WORK_MASK
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index d0537573501e..5e1fc4f82883 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -25,7 +25,7 @@ cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
>  				   -fno-builtin -fpic \
>  				   $(call cc-option,-mno-single-pic-base)
>  cflags-$(CONFIG_RISCV)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> -				   -fpic
> +				   -fpic $(DISABLE_STACKLEAK_PLUGIN)
>  
>  cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
>  
> -- 
> 2.25.1
> 

-- 
Kees Cook