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 <th...@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;
> +}
>
