[PATCH v2] m68k: virt: pass RNG seed via bootinfo block

["Jason A. Donenfeld" <Jason@zx2c4.com>]

This commit wires up bootinfo's RNG seed attribute so that Linux VMs can
have their RNG seeded from the earliest possible time in boot, just like
the "rng-seed" device tree property on those platforms. The link
contains the corresponding Linux patch.

Link: https://lore.kernel.org/lkml/20220626111509.330159-1-Jason@zx2c4.com/
Based-on: <20220625152318.120849-1-Jason@zx2c4.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 hw/m68k/bootinfo.h                               | 16 ++++++++++++++++
 hw/m68k/virt.c                                   |  7 +++++++
 .../standard-headers/asm-m68k/bootinfo-virt.h    |  1 +
 3 files changed, 24 insertions(+)

diff --git a/hw/m68k/bootinfo.h b/hw/m68k/bootinfo.h
index ff4e155a3c..bd8b212fd3 100644
--- a/hw/m68k/bootinfo.h
+++ b/hw/m68k/bootinfo.h
@@ -56,4 +56,20 @@
         stb_phys(as, base++, 0); \
         base = (base + 1) & ~1; \
     } while (0)
+
+#define BOOTINFODATA(as, base, id, data, len) \
+    do { \
+        int i; \
+        stw_phys(as, base, id); \
+        base += 2; \
+        stw_phys(as, base, \
+                 (sizeof(struct bi_record) + len + 3) & ~1); \
+        base += 2; \
+        stw_phys(as, base, len); \
+        base += 2; \
+        for (i = 0; i < len; ++i) { \
+            stb_phys(as, base++, data[i]); \
+        } \
+        base = (base + 1) & ~1; \
+    } while (0)
 #endif
diff --git a/hw/m68k/virt.c b/hw/m68k/virt.c
index e215aa3d42..0aa383fa6b 100644
--- a/hw/m68k/virt.c
+++ b/hw/m68k/virt.c
@@ -9,6 +9,7 @@
 
 #include "qemu/osdep.h"
 #include "qemu/units.h"
+#include "qemu/guest-random.h"
 #include "sysemu/sysemu.h"
 #include "cpu.h"
 #include "hw/boards.h"
@@ -120,6 +121,7 @@ static void virt_init(MachineState *machine)
     hwaddr io_base;
     int i;
     ResetInfo *reset_info;
+    uint8_t rng_seed[32];
 
     if (ram_size > 3399672 * KiB) {
         /*
@@ -245,6 +247,11 @@ static void virt_init(MachineState *machine)
                         kernel_cmdline);
         }
 
+	/* Pass seed to RNG. */
+	qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
+	BOOTINFODATA(cs->as, parameters_base, BI_VIRT_RNG_SEED,
+		     rng_seed, sizeof(rng_seed));
+
         /* load initrd */
         if (initrd_filename) {
             initrd_size = get_image_size(initrd_filename);
diff --git a/include/standard-headers/asm-m68k/bootinfo-virt.h b/include/standard-headers/asm-m68k/bootinfo-virt.h
index 81be1e0924..1b1ffd4705 100644
--- a/include/standard-headers/asm-m68k/bootinfo-virt.h
+++ b/include/standard-headers/asm-m68k/bootinfo-virt.h
@@ -12,6 +12,7 @@
 #define BI_VIRT_GF_TTY_BASE	0x8003
 #define BI_VIRT_VIRTIO_BASE	0x8004
 #define BI_VIRT_CTRL_BASE	0x8005
+#define BI_VIRT_RNG_SEED	0x8006
 
 #define VIRT_BOOTI_VERSION	MK_BI_VERSION(2, 0)
 
-- 
2.35.1