Re: [PATCH] hw/ppc: pass random seed to fdt

[Daniel Henrique Barboza]

On 7/12/22 10:51, Jason A. Donenfeld wrote:
> If the FDT contains /chosen/rng-seed, then the Linux RNG will use it to
> initialize early. Set this using the usual guest random number
> generation function. This is confirmed to successfully initialize the
> RNG on Linux 5.19-rc6. The rng-seed node is part of the DT spec. Set
> this on the paravirt platforms, spapr and e500, just as is done on other
> architectures with paravirt hardware.
>
> Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---

With current QEMU master, running a fedora 36 ppc64le guest with a
5.19.0-rc2-00054-g12ede8ffb103 kernel :

[root@fedora ~]# dmesg | grep -i rng
[    5.130623] random: crng init done
[root@fedora ~]#


After applying this patch:


[root@fedora ~]# dmesg | grep -i rng
[    0.000000] random: crng init done
[root@fedora ~]#



Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>




>   hw/ppc/e500.c  | 5 +++++
>   hw/ppc/spapr.c | 5 +++++
>   2 files changed, 10 insertions(+)
>
> diff --git a/hw/ppc/e500.c b/hw/ppc/e500.c
> index 7f7f5b3452..2f86eb490e 100644
> --- a/hw/ppc/e500.c
> +++ b/hw/ppc/e500.c
> @@ -17,6 +17,7 @@
>   #include "qemu/osdep.h"
>   #include "qemu/datadir.h"
>   #include "qemu/units.h"
> +#include "qemu/guest-random.h"
>   #include "qapi/error.h"
>   #include "e500.h"
>   #include "e500-ccsr.h"
> @@ -346,6 +347,7 @@ static int ppce500_load_device_tree(PPCE500MachineState 
> *pms,
>           };
>       const char *dtb_file = machine->dtb;
>       const char *toplevel_compat = machine->dt_compatible;
> +    uint8_t rng_seed[32];
>   
>       if (dtb_file) {
>           char *filename;
> @@ -403,6 +405,9 @@ static int ppce500_load_device_tree(PPCE500MachineState 
> *pms,
>       if (ret < 0)
>           fprintf(stderr, "couldn't set /chosen/bootargs\n");
>   
> +    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
> +    qemu_fdt_setprop(fdt, "/chosen", "rng-seed", rng_seed, sizeof(rng_seed));
> +
>       if (kvm_enabled()) {
>           /* Read out host's frequencies */
>           clock_freq = kvmppc_get_clockfreq();
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 9a5382d527..3a5112899e 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -27,6 +27,7 @@
>   #include "qemu/osdep.h"
>   #include "qemu/datadir.h"
>   #include "qemu/memalign.h"
> +#include "qemu/guest-random.h"
>   #include "qapi/error.h"
>   #include "qapi/qapi-events-machine.h"
>   #include "qapi/qapi-events-qdev.h"
> @@ -1014,6 +1015,7 @@ static void spapr_dt_chosen(SpaprMachineState *spapr, 
> void *fdt, bool reset)
>   {
>       MachineState *machine = MACHINE(spapr);
>       SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(machine);
> +    uint8_t rng_seed[32];
>       int chosen;
>   
>       _FDT(chosen = fdt_add_subnode(fdt, 0, "chosen"));
> @@ -1091,6 +1093,9 @@ static void spapr_dt_chosen(SpaprMachineState *spapr, 
> void *fdt, bool reset)
>           spapr_dt_ov5_platform_support(spapr, fdt, chosen);
>       }
>   
> +    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
> +    _FDT(fdt_setprop(fdt, chosen, "rng-seed", rng_seed, sizeof(rng_seed)));
> +
>       _FDT(spapr_dt_ovec(fdt, chosen, spapr->ov5_cas, 
> "ibm,architecture-vec-5"));
>   }
>