[PATCH] RISC-V: Add STACKLEAK erasing the kernel stack at the end of syscalls

[Conor.Dooley at microchip.com]

On 03/09/2022 17:23, guoren at kernel.org wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> From: Xianting Tian <xianting.tian at linux.alibaba.com>
> 
> This adds support for the STACKLEAK gcc plugin to RISC-V and disables
> the plugin in EFI stub code, which is out of scope for the protection.
> 
> For the benefits of STACKLEAK feature, please check the commit
> afaef01c0015 ("x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls")
> 
> Performance impact (tested on qemu env with 1 riscv64 hart, 1GB mem)
>     hackbench -s 512 -l 200 -g 15 -f 25 -P
>     2.0% slowdown
> 
> Signed-off-by: Xianting Tian <xianting.tian at linux.alibaba.com>

What changed since Xianting posted it himself a week ago:
https://lore.kernel.org/linux-riscv/20220828135407.3897717-1-xianting.tian@linux.alibaba.com/

There's an older patch from Du Lao adding STACKLEAK too:
https://lore.kernel.org/linux-riscv/20220615213834.3116135-1-daolu@rivosinc.com/

But since there's been no activity there since June...

> ---
>  arch/riscv/Kconfig                    | 1 +
>  arch/riscv/include/asm/processor.h    | 4 ++++
>  arch/riscv/kernel/entry.S             | 3 +++
>  drivers/firmware/efi/libstub/Makefile | 2 +-
>  4 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index ed66c31e4655..61fd0dad4463 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -85,6 +85,7 @@ config RISCV
>         select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
>         select HAVE_ARCH_THREAD_STRUCT_WHITELIST
>         select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
> +       select HAVE_ARCH_STACKLEAK
>         select HAVE_ASM_MODVERSIONS
>         select HAVE_CONTEXT_TRACKING_USER
>         select HAVE_DEBUG_KMEMLEAK
> 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
> 
> --
> 2.17.1
> 
> 
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