x86: reinitialize RNG seed on system reboot

Since this is read from fw_cfg on each boot, the kernel zeroing it out
alone is insufficient to prevent it from being used twice. And indeed on
reboot we always want a new seed, not the old one. So re-fill it in this
circumstance.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Message-Id: <20220921093134.2936487-3-Jason@zx2c4.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index 1ee0b1b413b35c5758884be1b74fd83e963b6e5d..f9a4ddaa4a31868b7d89174ad104e04dbdc6942b 100644 (file)
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -783,6 +783,12 @@ static void reset_setup_data(void *opaque)
     stq_p(fixup->pos, fixup->orig_val);
 }
 
+static void reset_rng_seed(void *opaque)
+{
+    SetupData *setup_data = opaque;
+    qemu_guest_getrandom_nofail(setup_data->data, le32_to_cpu(setup_data->len));
+}
+
 void x86_load_linux(X86MachineState *x86ms,
                     FWCfgState *fw_cfg,
                     int acpi_data_size,
@@ -1105,6 +1111,7 @@ void x86_load_linux(X86MachineState *x86ms,
         setup_data->type = cpu_to_le32(SETUP_RNG_SEED);
         setup_data->len = cpu_to_le32(RNG_SEED_LENGTH);
         qemu_guest_getrandom_nofail(setup_data->data, RNG_SEED_LENGTH);
+        qemu_register_reset(reset_rng_seed, setup_data);
     }
 
     fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, prot_addr);