Re: [PATCH v8 2/2] target/s390x: support PRNO_TRNG instruction

[Thomas Huth <thuth@redhat.com>]

On 21/09/2022 12.07, Jason A. Donenfeld wrote:
> In order for hosts running inside of TCG to initialize the kernel's
> random number generator, we should support the PRNO_TRNG instruction,
> backed in the usual way with the qemu_guest_getrandom helper. This is
> confirmed working on Linux 5.19.
> 
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Cc: Harald Freudenberger <freude@linux.ibm.com>
> Cc: Holger Dengler <dengler@linux.ibm.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>   target/s390x/gen-features.c      |  1 +
>   target/s390x/tcg/crypto_helper.c | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 31 insertions(+)
> 
> diff --git a/target/s390x/gen-features.c b/target/s390x/gen-features.c
> index 14a7f2ae90..aaade67574 100644
> --- a/target/s390x/gen-features.c
> +++ b/target/s390x/gen-features.c
> @@ -754,6 +754,7 @@ static uint16_t qemu_MAX[] = {
>       S390_FEAT_MSA_EXT_5,
>       S390_FEAT_KIMD_SHA_512,
>       S390_FEAT_KLMD_SHA_512,
> +    S390_FEAT_PRNO_TRNG,
>   };
>   
>   /****** END FEATURE DEFS ******/
> diff --git a/target/s390x/tcg/crypto_helper.c b/target/s390x/tcg/crypto_helper.c
> index 02073ec70b..0daa9a2dd9 100644
> --- a/target/s390x/tcg/crypto_helper.c
> +++ b/target/s390x/tcg/crypto_helper.c
> @@ -14,6 +14,7 @@
>   
>   #include "qemu/osdep.h"
>   #include "qemu/main-loop.h"
> +#include "qemu/guest-random.h"
>   #include "s390x-internal.h"
>   #include "tcg_s390x.h"
>   #include "exec/helper-proto.h"
> @@ -173,6 +174,31 @@ static int klmd_sha512(CPUS390XState *env, uintptr_t ra, uint64_t parameter_bloc
>       return 0;
>   }
>   
> +static void fill_buf_random(CPUS390XState *env, uintptr_t ra,
> +                            uint64_t *buf_reg, uint64_t *len_reg)
> +{
> +    uint8_t tmp[256];
> +    uint64_t len = *len_reg;
> +    int buf_reg_len = 64;
> +
> +    if (!(env->psw.mask & PSW_MASK_64)) {
> +        len = (uint32_t)len;
> +        buf_reg_len = (env->psw.mask & PSW_MASK_32) ? 32 : 24;
> +    }
> +
> +    while (len) {
> +        size_t block = MIN(len, sizeof(tmp));
> +
> +        qemu_guest_getrandom_nofail(tmp, block);
> +        for (size_t i = 0; i < block; ++i) {
> +            cpu_stb_data_ra(env, wrap_address(env, *buf_reg), tmp[i], ra);
> +            *buf_reg = deposit64(*buf_reg, 0, buf_reg_len, *buf_reg + 1);
> +            --*len_reg;
> +        }
> +        len -= block;
> +    }
> +}
> +
>   uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3,
>                        uint32_t type)
>   {
> @@ -215,6 +241,10 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3,
>               return klmd_sha512(env, ra, env->regs[1], &env->regs[r2], &env->regs[r2 + 1]);
>           }
>           break;
> +    case 114: /* CPACF_PRNO_TRNG */
> +        fill_buf_random(env, ra, &env->regs[r1], &env->regs[r1 + 1]);
> +        fill_buf_random(env, ra, &env->regs[r2], &env->regs[r2 + 1]);
> +        break;

Thanks, patch looks fine to me!

(if we ever have another instruction that uses fc 114, we might want to 
check "type" here, too, but that can also be added later, of course)

  Thomas