linux-kernel - [PATCH v3 2/3] m68k: virt: generate new RNG seed on reboot

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Date:   Fri, 23 Sep 2022 19:03:39 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH v3 2/3] m68k: virt: generate new RNG seed on reboot

Rather than rebooting into a system with no entropy, regenerate the RNG
seed before rebooting, so that the new system has a fresh seed.

Fixes: a1ee38ab1a75 ("m68k: virt: Use RNG seed from bootinfo block")
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 arch/m68k/virt/config.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/m68k/virt/config.c b/arch/m68k/virt/config.c
index 4ab22946ff68..d4627840e35b 100644
--- a/arch/m68k/virt/config.c
+++ b/arch/m68k/virt/config.c
@@ -45,10 +45,18 @@ static void virt_halt(void)
 		;
 }
 
+static const struct bi_record *rng_seed_record;
+
 static void virt_reset(void)
 {
 	void __iomem *base = (void __iomem *)virt_bi_data.ctrl.mmio;
 
+	if (rng_seed_record && rng_seed_record->size > sizeof(*rng_seed_record) + 2) {
+		u16 len = rng_seed_record->size - sizeof(*rng_seed_record) - 2;
+		get_random_bytes((u8 *)rng_seed_record->data + 2, len);
+		*(u16 *)rng_seed_record->data = cpu_to_be16(len);
+	}
+
 	iowrite32be(CMD_RESET, base + VIRT_CTRL_REG_CMD);
 	local_irq_disable();
 	while (1)
@@ -101,6 +109,8 @@ int __init virt_parse_bootinfo(const struct bi_record *record)
 		 * length to prevent kexec from using it.
 		 */
 		memzero_explicit((void *)data, len + 2);
+		/* Store a reference to be filled in on reboot. */
+		rng_seed_record = record;
 		break;
 	}
 	default:
-- 
2.37.3