[PATCH v4 4/4] lib: sbi: fwft: implement landing pad and shadow stack fwft interface

[Clément Léger]

On 23/08/2024 20:47, Deepak Gupta wrote:
> Supervisor software can enable control flow integrity features for itself
> using fwft feature `SBI_FWFT_LANDING_PAD` and `SBI_FWFT_SHADOW_STACK`.
> This patch implements the mechanism to enable both these fwft.
> 
> Signed-off-by: Deepak Gupta <debug at rivosinc.com>
> ---
>  lib/sbi/sbi_fwft.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 74 insertions(+)
> 
> diff --git a/lib/sbi/sbi_fwft.c b/lib/sbi/sbi_fwft.c
> index ef881ef..747bc88 100644
> --- a/lib/sbi/sbi_fwft.c
> +++ b/lib/sbi/sbi_fwft.c
> @@ -145,6 +145,68 @@ static int fwft_get_adue(struct fwft_config *conf, unsigned long *value)
>  	return SBI_OK;
>  }
>  
> +static int fwft_lpad_supported(struct fwft_config *conf)
> +{
> +	if (!sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
> +				    SBI_HART_EXT_ZICFILP))
> +		return SBI_ENOTSUPP;
> +
> +	return SBI_OK;
> +}
> +
> +static int fwft_enable_lpad(struct fwft_config *conf, unsigned long value)
> +{
> +	if (value == 1)
> +		csr_set(CSR_MENVCFG, ENVCFG_LPE);
> +	else if (value == 0)
> +		csr_clear(CSR_MENVCFG, ENVCFG_LPE);
> +	else
> +		return SBI_EINVAL;
> +
> +	return SBI_OK;
> +}
> +
> +static int fwft_get_lpad(struct fwft_config *conf, unsigned long *value)
> +{
> +	unsigned long cfg;
> +
> +	cfg = csr_read(CSR_MENVCFG) & ENVCFG_LPE;
> +	*value = cfg != 0;
> +
> +	return SBI_OK;
> +}
> +
> +static int fwft_sstack_supported(struct fwft_config *conf)
> +{
> +	if (!sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
> +				    SBI_HART_EXT_ZICFISS))
> +		return SBI_ENOTSUPP;
> +
> +	return SBI_OK;
> +}
> +
> +static int fwft_enable_sstack(struct fwft_config *conf, unsigned long value)
> +{
> +	if (value == 1)
> +		csr_set(CSR_MENVCFG, ENVCFG_SSE);
> +	else if (value == 0)
> +		csr_clear(CSR_MENVCFG, ENVCFG_SSE);
> +	else
> +		return SBI_EINVAL;
> +
> +	return SBI_OK;
> +}
> +
> +static int fwft_get_sstack(struct fwft_config *conf, unsigned long *value)
> +{
> +	unsigned long cfg;
> +
> +	cfg = csr_read(CSR_MENVCFG) & ENVCFG_SSE;
> +	*value = cfg != 0;
> +
> +	return SBI_OK;
> +}
> +
>  static struct fwft_config* get_feature_config(enum sbi_fwft_feature_t feature)
>  {
>  	int i;
> @@ -236,6 +298,18 @@ static const struct fwft_feature features[] =
>  		.set = fwft_set_adue,
>  		.get = fwft_get_adue,
>  	},
> +	{
> +		.id = SBI_FWFT_LANDING_PAD,
> +		.supported = fwft_lpad_supported,
> +		.set = fwft_enable_lpad,
> +		.get = fwft_get_lpad,
> +	},
> +	{
> +		.id = SBI_FWFT_SHADOW_STACK,
> +		.supported = fwft_sstack_supported,
> +		.set = fwft_enable_sstack,
> +		.get = fwft_get_sstack,
> +	},
>  };
>  
>  int sbi_fwft_init(struct sbi_scratch *scratch, bool cold_boot)


Hey Deepak,

LGTM, the only thing that could be done (but I guess that'll be for me
when I submit the double trap feature) is factorizing the MENVCFG
read/write function since we'll have 3 features doing almost the same thing.

But that's really optional for you.

Reviewed-by: Clément Léger <cleger at rivosinc.com>