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

Radim Krčmář
2025-03-20T21:36:08Z

2025-03-14T14:39:42-07:00, Deepak Gupta <debug@rivosinc.com>:
> This commit adds a kernel command line option using which user cfi can be
> disabled.
>
> Signed-off-by: Deepak Gupta <debug@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.