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

[Deepak Gupta]

On Tue, Sep 10, 2024 at 08:59:00AM +0200, Clément Léger wrote:
>
>
>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.
>

Since you've thoughts on this on how to handle it, I'll leave it for you.

>But that's really optional for you.
>
>Reviewed-by: Clément Léger <cleger at rivosinc.com>

Thanks.