Re: [PATCH v2] riscv: enable HAVE_ARCH_STACKLEAK

[Charlie Jenkins <charlie@rivosinc.com>]

On Mon, Jun 24, 2024 at 07:53:16AM +0800, Jisheng Zhang wrote:
> Add support for the stackleak feature. Whenever the kernel returns to user
> space the kernel stack is filled with a poison value.
> 
> At the same time, disables the plugin in EFI stub code because EFI stub
> is out of scope for the protection.
> 
> Tested on qemu and milkv duo:
> / # echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT
> [   38.675575] lkdtm: Performing direct entry STACKLEAK_ERASING
> [   38.678448] lkdtm: stackleak stack usage:
> [   38.678448]   high offset: 288 bytes
> [   38.678448]   current:     496 bytes
> [   38.678448]   lowest:      1328 bytes
> [   38.678448]   tracked:     1328 bytes
> [   38.678448]   untracked:   448 bytes
> [   38.678448]   poisoned:    14312 bytes
> [   38.678448]   low offset:  8 bytes
> [   38.689887] lkdtm: OK: the rest of the thread stack is properly erased
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
> 
> since v2:
>  - add #include <linux/sizes.h> to fixing compiler error found by
>    Charlie

Thanks!

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>

> 
>  arch/riscv/Kconfig                    | 1 +
>  arch/riscv/include/asm/thread_info.h  | 1 +
>  arch/riscv/kernel/entry.S             | 4 ++++
>  drivers/firmware/efi/libstub/Makefile | 3 ++-
>  4 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 0525ee2d63c7..9cbfdffec96c 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -118,6 +118,7 @@ config RISCV
>  	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>  	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
>  	select HAVE_ARCH_SECCOMP_FILTER
> +	select HAVE_ARCH_STACKLEAK
>  	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
>  	select HAVE_ARCH_TRACEHOOK
>  	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> index 5d473343634b..fca5c6be2b81 100644
> --- a/arch/riscv/include/asm/thread_info.h
> +++ b/arch/riscv/include/asm/thread_info.h
> @@ -10,6 +10,7 @@
>  
>  #include <asm/page.h>
>  #include <linux/const.h>
> +#include <linux/sizes.h>
>  
>  /* thread information allocation */
>  #define THREAD_SIZE_ORDER	CONFIG_THREAD_SIZE_ORDER
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 68a24cf9481a..80ff55a26d13 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -130,6 +130,10 @@ SYM_CODE_START_NOALIGN(ret_from_exception)
>  #endif
>  	bnez s0, 1f
>  
> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
> +	call	stackleak_erase_on_task_stack
> +#endif
> +
>  	/* Save unwound kernel stack pointer in thread_info */
>  	addi s0, sp, PT_SIZE_ON_STACK
>  	REG_S s0, TASK_TI_KERNEL_SP(tp)
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 06f0428a723c..3a9521c57641 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -28,7 +28,8 @@ cflags-$(CONFIG_ARM)		+= -DEFI_HAVE_STRLEN -DEFI_HAVE_STRNLEN \
>  				   -DEFI_HAVE_MEMCHR -DEFI_HAVE_STRRCHR \
>  				   -DEFI_HAVE_STRCMP -fno-builtin -fpic \
>  				   $(call cc-option,-mno-single-pic-base)
> -cflags-$(CONFIG_RISCV)		+= -fpic -DNO_ALTERNATIVE -mno-relax
> +cflags-$(CONFIG_RISCV)		+= -fpic -DNO_ALTERNATIVE -mno-relax \
> +				   $(DISABLE_STACKLEAK_PLUGIN)
>  cflags-$(CONFIG_LOONGARCH)	+= -fpie
>  
>  cflags-$(CONFIG_EFI_PARAMS_FROM_FDT)	+= -I$(srctree)/scripts/dtc/libfdt
> -- 
> 2.43.0
>