m68k: virt: Use RNG seed from bootinfo block

Other virt VMs can pass RNG seeds via the "rng-seed" device tree
property or via UEFI, but m68k doesn't have either. Instead it has its
own bootinfo protocol. So this commit adds support for receiving a RNG
seed from it, which will be used at the earliest possible time in boot,
just like device tree.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://lore.kernel.org/r/20220626111509.330159-1-Jason@zx2c4.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

diff --git a/arch/m68k/include/uapi/asm/bootinfo-virt.h b/arch/m68k/include/uapi/asm/bootinfo-virt.h
index e4db7e2..b091ee9 100644 (file)
--- a/arch/m68k/include/uapi/asm/bootinfo-virt.h
+++ b/arch/m68k/include/uapi/asm/bootinfo-virt.h
@@ -13,6 +13,14 @@
 #define BI_VIRT_VIRTIO_BASE    0x8004
 #define BI_VIRT_CTRL_BASE      0x8005
 
+/*
+ * A random seed used to initialize the RNG. Record format:
+ *
+ *   - length       [ 2 bytes, 16-bit big endian ]
+ *   - seed data    [ `length` bytes, padded to preserve 2-byte alignment ]
+ */
+#define BI_VIRT_RNG_SEED       0x8006
+
 #define VIRT_BOOTI_VERSION     MK_BI_VERSION(2, 0)
 
 #endif /* _UAPI_ASM_M68K_BOOTINFO_MAC_H */

diff --git a/arch/m68k/virt/config.c b/arch/m68k/virt/config.c
index 632ba20..4ab2294 100644 (file)
--- a/arch/m68k/virt/config.c
+++ b/arch/m68k/virt/config.c
@@ -2,6 +2,7 @@
 
 #include <linux/reboot.h>
 #include <linux/serial_core.h>
+#include <linux/random.h>
 #include <clocksource/timer-goldfish.h>
 
 #include <asm/bootinfo.h>
@@ -92,6 +93,16 @@ int __init virt_parse_bootinfo(const struct bi_record *record)
                data += 4;
                virt_bi_data.virtio.irq = be32_to_cpup(data);
                break;
+       case BI_VIRT_RNG_SEED: {
+               u16 len = be16_to_cpup(data);
+               add_bootloader_randomness(data + 2, len);
+               /*
+                * Zero the data to preserve forward secrecy, and zero the
+                * length to prevent kexec from using it.
+                */
+               memzero_explicit((void *)data, len + 2);
+               break;
+       }
        default:
                unknown = 1;
                break;