[PATCH 05/11] riscv: enable landing pad enforcement

[Heinrich Schuchardt]

On 25.07.25 01:36, Deepak Gupta wrote:
> Enables landing pad enforcement by invoking a SBI FWFT call.
> 
> Signed-off-by: Deepak Gupta <debug at rivosinc.com>
> ---
>   arch/riscv/kernel/asm-offsets.c |  1 +
>   arch/riscv/kernel/head.S        | 19 +++++++++++++++++++
>   2 files changed, 20 insertions(+)
> 
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index e4d55126dc3e..e6a9fad86fae 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -536,6 +536,7 @@ void asm_offsets(void)
>   	DEFINE(SBI_EXT_FWFT, SBI_EXT_FWFT);
>   	DEFINE(SBI_EXT_FWFT_SET, SBI_EXT_FWFT_SET);
>   	DEFINE(SBI_FWFT_SHADOW_STACK, SBI_FWFT_SHADOW_STACK);
> +	DEFINE(SBI_FWFT_LANDING_PAD, SBI_FWFT_LANDING_PAD);
>   	DEFINE(SBI_FWFT_SET_FLAG_LOCK, SBI_FWFT_SET_FLAG_LOCK);
>   #endif
>   }
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 9c99c5ad6fe8..59af044bf85c 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -185,6 +185,16 @@ secondary_start_sbi:
>   1:
>   #endif
>   	scs_load_current
> +
> +#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_KERNEL_CFI)
> +	li a7, SBI_EXT_FWFT
> +	li a6, SBI_EXT_FWFT_SET
> +	li a0, SBI_FWFT_LANDING_PAD
> +	li a1, 1 /* enable landing pad for supervisor */
> +	li a2, SBI_FWFT_SET_FLAG_LOCK
> +	ecall	/* check for error condition and take appropriate action */
> +#endif
> +
>   	call smp_callin
>   #endif /* CONFIG_SMP */
>   
> @@ -359,6 +369,15 @@ SYM_CODE_START(_start_kernel)
>   #endif
>   	scs_load_current
>   
> +#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_KERNEL_CFI)
> +	li a7, SBI_EXT_FWFT
> +	li a6, SBI_EXT_FWFT_SET
> +	li a0, SBI_FWFT_LANDING_PAD
> +	li a1, 1 /* enable landing pad for supervisor */

The SBI specification calls BIT(0) "LOCK".
Shouldn't we define a constant for the lock bit instead of using a magic 
value?

Best regards

Heinrich

> +	li a2, SBI_FWFT_SET_FLAG_LOCK
> +	ecall	/* check for error condition and take appropriate action */
> +#endif
> +
>   #ifdef CONFIG_KASAN
>   	call kasan_early_init
>   #endif
>