spapr: Generate random HASHPKEYR for spapr machines

The hypervisor is expected to create a value for the HASHPKEY SPR for
each partition. Currently it uses zero for all partitions, use a
random number instead, which in theory might make kernel ROP protection
more secure.

Signed-of-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20241219034035.1826173-4-npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

hw/ppc/spapr.c

@@ -2917,6 +2917,9 @@ static void spapr_machine_init(MachineState *machine)
         spapr_ovec_set(spapr->ov5, OV5_XIVE_EXPLOIT);
     }
 
+    qemu_guest_getrandom_nofail(&spapr->hashpkey_val,
+                                sizeof(spapr->hashpkey_val));
+
     /* init CPUs */
     spapr_init_cpus(spapr);
 

hw/ppc/spapr_cpu_core.c

@@ -273,6 +273,8 @@ static bool spapr_realize_vcpu(PowerPCCPU *cpu, SpaprMachineState *spapr,
     env->spr_cb[SPR_PIR].default_value = cs->cpu_index;
     env->spr_cb[SPR_TIR].default_value = thread_index;
 
+    env->spr_cb[SPR_HASHPKEYR].default_value = spapr->hashpkey_val;
+
     cpu_ppc_set_1lpar(cpu);
 
     /* Set time-base frequency to 512 MHz. vhyp must be set first. */

include/hw/ppc/spapr.h

@@ -203,6 +203,7 @@ struct SpaprMachineState {
     uint32_t fdt_initial_size;
     void *fdt_blob;
     uint8_t fdt_rng_seed[32];
+    uint64_t hashpkey_val;
     long kernel_size;
     bool kernel_le;
     uint64_t kernel_addr;