From b7a5d1e66c47bf686736a9ef842c65b9bcc1bb75 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Mon, 24 Feb 2020 14:46:41 +0100
Subject: [efi] Consider RDRAND == -1 invalid, use TSC

---
 src/interface/efi/efi_entropy.c | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'src/interface/efi/efi_entropy.c')

diff --git a/src/interface/efi/efi_entropy.c b/src/interface/efi/efi_entropy.c
index a1dfaaa79..a865bad59 100644
--- a/src/interface/efi/efi_entropy.c
+++ b/src/interface/efi/efi_entropy.c
@@ -170,6 +170,10 @@ static int efi_get_noise_rdrand ( noise_sample_t *noise ) {
 		while ( --retries > 0 ) {
 			__asm__ volatile ( "rdrand %0; setc %1" : "=r" ( ret ), "=qm" ( ok ) );
 			if ( ok ) {
+				if ( ret == -1 ) {
+					/* Assume this is a broken AMD CPU, fall back to TSC */
+					ret = profile_timestamp();
+				}
 				*noise = ret;
 				return 0;
 			}
-- 
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