Re: [Qemu-devel] [Qemu-ppc] [RFC PATCH] ppc/spapr_hcall: Implement H_RANDOM hypercall

[Laurent Vivier <lvivier@redhat.com>]

Hi,

As "/dev/random" can be blocking perhaps it is possible/better to use
the QEMU rng backend instead ?

Laurent

On 06/08/2015 10:23, Thomas Huth wrote:
> The spapr firmware SLOF likely needs a way to get random numbers
> soon. Instead of re-inventing the wheel there, we could simply
> use the H_RANDOM hypercall to get the random numbers from QEMU.
> For this the H_RANDOM hypercall needs to be implemented first, of
> course.
> So this patch introduces an OS-specifc helper function called
> qemu_random() to get "good" random numbers (from /dev/random on
> POSIX systems and via CryptGenRandom() on Windows), and then uses
> this helper functions to provide random data to the guest via the
> H_RANDOM hypercall.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  Note: Since I do not have access to the SPAPR spec, I figured out
>  the calling conventions of the hypercall by looking at the way
>  the Linux kernel is using this call to retriev random data. So
>  there might be some bugs or missing pieces here.
> 
>  Also note that the Windows version of qemu_random() is
>  compile-tested only (with a MinGW cross-compiler), since I do not
>  have access to a Windows  system right now.
> 
>  hw/ppc/spapr_hcall.c   | 12 ++++++++++++
>  include/hw/ppc/spapr.h |  1 +
>  include/qemu/osdep.h   | 11 +++++++++++
>  util/oslib-posix.c     | 16 ++++++++++++++++
>  util/oslib-win32.c     | 17 +++++++++++++++++
>  5 files changed, 57 insertions(+)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index fcfb50c..30f4359 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -931,6 +931,15 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu_,
>      return H_SUCCESS;
>  }
>  
> +static target_ulong h_random(PowerPCCPU *cpu, sPAPRMachineState *spapr,
> +                             target_ulong opcode, target_ulong *args)
> +{
> +    if (qemu_random(&args[0], sizeof(args[0]))) {
> +        return H_HARDWARE;
> +    }
> +    return H_SUCCESS;
> +}
> +
>  static spapr_hcall_fn papr_hypercall_table[(MAX_HCALL_OPCODE / 4) + 1];
>  static spapr_hcall_fn kvmppc_hypercall_table[KVMPPC_HCALL_MAX - KVMPPC_HCALL_BASE + 1];
>  
> @@ -1016,6 +1025,9 @@ static void hypercall_register_types(void)
>  
>      /* ibm,client-architecture-support support */
>      spapr_register_hypercall(KVMPPC_H_CAS, h_client_architecture_support);
> +
> +    /* misc */
> +    spapr_register_hypercall(H_RANDOM, h_random);
>  }
>  
>  type_init(hypercall_register_types)
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 46e9704..232cda1 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -331,6 +331,7 @@ struct sPAPRMachineState {
>  #define H_SET_MPP               0x2D0
>  #define H_GET_MPP               0x2D4
>  #define H_XIRR_X                0x2FC
> +#define H_RANDOM                0x300
>  #define H_SET_MODE              0x31C
>  #define MAX_HCALL_OPCODE        H_SET_MODE
>  
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 3247364..1ef0f11 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -261,4 +261,15 @@ void os_mem_prealloc(int fd, char *area, size_t sz);
>  
>  int qemu_read_password(char *buf, int buf_size);
>  
> +/**
> + * qemu_random:
> + * @buf: pointer to the buffer where the values should be stored
> + * @size: amount of bytes that should be stored
> + *
> + * Retrieve random numbers, store them in @buf.
> + *
> + * Returns: 0 on success, error code otherwise
> + */
> +int qemu_random(void *buf, int size);
> +
>  #endif
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 3ae4987..43f5a51 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -482,3 +482,19 @@ int qemu_read_password(char *buf, int buf_size)
>      printf("\n");
>      return ret;
>  }
> +
> +int qemu_random(void *buf, int size)
> +{
> +    FILE *fh;
> +
> +    fh = fopen("/dev/random", "rb");
> +    if (!fh) {
> +        return -errno;
> +    }
> +    if (fread(buf, 1, size, fh) != size) {
> +        return -EIO;
> +    }
> +    fclose(fh);
> +
> +    return 0;
> +}
> diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> index 730a670..63f0a94 100644
> --- a/util/oslib-win32.c
> +++ b/util/oslib-win32.c
> @@ -494,3 +494,20 @@ int qemu_read_password(char *buf, int buf_size)
>      buf[i] = '\0';
>      return 0;
>  }
> +
> +int qemu_random(void *buf, int size)
> +{
> +    HCRYPTPROV hprov = 0;
> +    int ret = 0;
> +
> +    if (!CryptAcquireContext(&hprov, NULL, NULL, PROV_RSA_FULL,
> +                             CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
> +        return -EINVAL;
> +    }
> +    if (!CryptGenRandom(hprov, size, buf)) {
> +        ret = -EIO;
> +    }
> +    CryptReleaseContext(hprov, 0);
> +
> +    return ret;
> +}
>