[PATCH v12 23/28] riscv: kernel command line option to opt out of user cfi

[Radim Krčmář]

2025-03-14T14:39:42-07:00, Deepak Gupta <debug at rivosinc.com>:
> This commit adds a kernel command line option using which user cfi can be
> disabled.
>
> Signed-off-by: Deepak Gupta <debug at rivosinc.com>
> ---
>  arch/riscv/kernel/usercfi.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
> index d31d89618763..813162ce4f15 100644
> --- a/arch/riscv/kernel/usercfi.c
> +++ b/arch/riscv/kernel/usercfi.c
> @@ -17,6 +17,8 @@
>  #include <asm/csr.h>
>  #include <asm/usercfi.h>
>  
> +bool disable_riscv_usercfi;
> +
>  #define SHSTK_ENTRY_SIZE sizeof(void *)
>  
>  bool is_shstk_enabled(struct task_struct *task)
> @@ -396,6 +398,9 @@ int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
>  	unsigned long size = 0, addr = 0;
>  	bool enable_shstk = false;
>  
> +	if (disable_riscv_usercfi)
> +		return 0;
> +
>  	if (!cpu_supports_shadow_stack())
>  		return -EINVAL;
>  
> @@ -475,6 +480,9 @@ int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status)
>  {
>  	bool enable_indir_lp = false;
>  
> +	if (disable_riscv_usercfi)
> +		return 0;
> +
>  	if (!cpu_supports_indirect_br_lp_instr())
>  		return -EINVAL;
>  
> @@ -507,3 +515,16 @@ int arch_lock_indir_br_lp_status(struct task_struct *task,
>  
>  	return 0;
>  }
> +
> +static int __init setup_global_riscv_enable(char *str)
> +{
> +	if (strcmp(str, "true") == 0)
> +		disable_riscv_usercfi = true;
> +
> +	pr_info("Setting riscv usercfi to be %s\n",
> +		(disable_riscv_usercfi ? "disabled" : "enabled"));
> +
> +	return 1;
> +}
> +
> +__setup("disable_riscv_usercfi=", setup_global_riscv_enable);

I'd prefer two command line options instead.

In any case, I think we still document params in kernel-parameters.txt.