Re: [PATCH v11 12/14] target/riscv: rvk: add CSR support for Zkr

[Alistair Francis]

On Tue, Apr 19, 2022 at 12:06 PM Weiwei Li <liweiwei@iscas.ac.cn> wrote:
>
>  - add SEED CSR which must be accessed with a read-write instruction:
>    A read-only instruction such as CSRRS/CSRRC with rs1=x0 or CSRRSI/CSRRCI
> with uimm=0 will raise an illegal instruction exception.
>  - add USEED, SSEED fields for MSECCFG CSR
>
> Co-authored-by: Ruibo Lu <luruibo2000@163.com>
> Co-authored-by: Zewen Ye <lustrew@foxmail.com>
> Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
> Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_bits.h  |  9 +++++
>  target/riscv/csr.c       | 80 ++++++++++++++++++++++++++++++++++++++++
>  target/riscv/op_helper.c |  9 +++++
>  target/riscv/pmp.h       |  8 ++--
>  4 files changed, 103 insertions(+), 3 deletions(-)
>
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index bb47cf7e77..d401100f47 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -458,6 +458,9 @@
>  #define CSR_VSPMMASK        0x2c1
>  #define CSR_VSPMBASE        0x2c2
>
> +/* Crypto Extension */
> +#define CSR_SEED            0x015
> +
>  /* mstatus CSR bits */
>  #define MSTATUS_UIE         0x00000001
>  #define MSTATUS_SIE         0x00000002
> @@ -800,4 +803,10 @@ typedef enum RISCVException {
>  #define HVICTL_VALID_MASK                  \
>      (HVICTL_VTI | HVICTL_IID | HVICTL_IPRIOM | HVICTL_IPRIO)
>
> +/* seed CSR bits */
> +#define SEED_OPST                        (0b11 << 30)
> +#define SEED_OPST_BIST                   (0b00 << 30)
> +#define SEED_OPST_WAIT                   (0b01 << 30)
> +#define SEED_OPST_ES16                   (0b10 << 30)
> +#define SEED_OPST_DEAD                   (0b11 << 30)
>  #endif
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index e10f691a99..865ffb36ce 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -24,6 +24,8 @@
>  #include "qemu/main-loop.h"
>  #include "exec/exec-all.h"
>  #include "sysemu/cpu-timers.h"
> +#include "qemu/guest-random.h"
> +#include "qapi/error.h"
>
>  /* CSR function table public API */
>  void riscv_get_csr_ops(int csrno, riscv_csr_operations *ops)
> @@ -301,6 +303,46 @@ static RISCVException debug(CPURISCVState *env, int 
> csrno)
>  }
>  #endif
>
> +static RISCVException seed(CPURISCVState *env, int csrno)
> +{
> +    RISCVCPU *cpu = env_archcpu(env);
> +
> +    if (!cpu->cfg.ext_zkr) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
> +#if !defined(CONFIG_USER_ONLY)
> +    /*
> +     * With a CSR read-write instruction:
> +     * 1) The seed CSR is always available in machine mode as normal.
> +     * 2) Attempted access to seed from virtual modes VS and VU always raises
> +     * an exception(virtual instruction exception only if mseccfg.sseed=1).
> +     * 3) Without the corresponding access control bit set to 1, any 
> attempted
> +     * access to seed from U, S or HS modes will raise an illegal instruction
> +     * exception.
> +     */
> +    if (env->priv == PRV_M) {
> +        return RISCV_EXCP_NONE;
> +    } else if (riscv_cpu_virt_enabled(env)) {
> +        if (env->mseccfg & MSECCFG_SSEED) {
> +            return RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
> +        } else {
> +            return RISCV_EXCP_ILLEGAL_INST;
> +        }
> +    } else {
> +        if (env->priv == PRV_S && (env->mseccfg & MSECCFG_SSEED)) {
> +            return RISCV_EXCP_NONE;
> +        } else if (env->priv == PRV_U && (env->mseccfg & MSECCFG_USEED)) {
> +            return RISCV_EXCP_NONE;
> +        } else {
> +            return RISCV_EXCP_ILLEGAL_INST;
> +        }
> +    }
> +#else
> +    return RISCV_EXCP_NONE;
> +#endif
> +}
> +
>  /* User Floating-Point CSRs */
>  static RISCVException read_fflags(CPURISCVState *env, int csrno,
>                                    target_ulong *val)
> @@ -3014,6 +3056,41 @@ static RISCVException write_upmbase(CPURISCVState 
> *env, int csrno,
>
>  #endif
>
> +/* Crypto Extension */
> +static RISCVException rmw_seed(CPURISCVState *env, int csrno,
> +                               target_ulong *ret_value,
> +                               target_ulong new_value,
> +                               target_ulong write_mask)
> +{
> +    uint16_t random_v;
> +    Error *random_e = NULL;
> +    int random_r;
> +    target_ulong rval;
> +
> +    random_r = qemu_guest_getrandom(&random_v, 2, &random_e);
> +    if (unlikely(random_r < 0)) {
> +        /*
> +         * Failed, for unknown reasons in the crypto subsystem.
> +         * The best we can do is log the reason and return a
> +         * failure indication to the guest.  There is no reason
> +         * we know to expect the failure to be transitory, so
> +         * indicate DEAD to avoid having the guest spin on WAIT.
> +         */
> +        qemu_log_mask(LOG_UNIMP, "%s: Crypto failure: %s",
> +                      __func__, error_get_pretty(random_e));
> +        error_free(random_e);
> +        rval = SEED_OPST_DEAD;
> +    } else {
> +        rval = random_v | SEED_OPST_ES16;
> +    }
> +
> +    if (ret_value) {
> +        *ret_value = rval;
> +    }
> +
> +    return RISCV_EXCP_NONE;
> +}
> +
>  /*
>   * riscv_csrrw - read and/or update control and status register
>   *
> @@ -3258,6 +3335,9 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
>      [CSR_TIME]  = { "time",  ctr,   read_time  },
>      [CSR_TIMEH] = { "timeh", ctr32, read_timeh },
>
> +    /* Crypto Extension */
> +    [CSR_SEED] = { "seed", seed, NULL, NULL, rmw_seed },
> +
>  #if !defined(CONFIG_USER_ONLY)
>      /* Machine Timers and Counters */
>      [CSR_MCYCLE]    = { "mcycle",    any,   read_instret  },
> diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
> index e0d708091e..3d8443416d 100644
> --- a/target/riscv/op_helper.c
> +++ b/target/riscv/op_helper.c
> @@ -39,6 +39,15 @@ void helper_raise_exception(CPURISCVState *env, uint32_t 
> exception)
>
>  target_ulong helper_csrr(CPURISCVState *env, int csr)
>  {
> +    /*
> +     * The seed CSR must be accessed with a read-write instruction. A
> +     * read-only instruction such as CSRRS/CSRRC with rs1=x0 or CSRRSI/
> +     * CSRRCI with uimm=0 will raise an illegal instruction exception.
> +     */
> +    if (csr == CSR_SEED) {
> +        riscv_raise_exception(env, RISCV_EXCP_ILLEGAL_INST, GETPC());
> +    }
> +
>      target_ulong val = 0;
>      RISCVException ret = riscv_csrrw(env, csr, &val, 0, 0, false);
>
> diff --git a/target/riscv/pmp.h b/target/riscv/pmp.h
> index fcb6b7c467..a8dd797476 100644
> --- a/target/riscv/pmp.h
> +++ b/target/riscv/pmp.h
> @@ -39,9 +39,11 @@ typedef enum {
>  } pmp_am_t;
>
>  typedef enum {
> -    MSECCFG_MML  = 1 << 0,
> -    MSECCFG_MMWP = 1 << 1,
> -    MSECCFG_RLB  = 1 << 2
> +    MSECCFG_MML   = 1 << 0,
> +    MSECCFG_MMWP  = 1 << 1,
> +    MSECCFG_RLB   = 1 << 2,
> +    MSECCFG_USEED = 1 << 8,
> +    MSECCFG_SSEED = 1 << 9
>  } mseccfg_field_t;
>
>  typedef struct {
> --
> 2.17.1
>
>