From 4fa6301523bc9d4fad1f6c2f6b6a7b9a8e40d758 Mon Sep 17 00:00:00 2001
From: 3541 <alex@emobrien.com>
Date: Sat, 27 Jun 2020 15:15:54 +1000
Subject: [PATCH] Kernel: Add g_cpu_supports_rdseed

CPUs which support RDRAND do not necessarily support RDSEED. This
introduces a flag g_cpu_supports_rdseed which is set appropriately
by CPUID. This causes Haswell CPUs in particular (and probably a lot
of AMD chips) to now fail to boot with #2634, rather than an illegal
instruction.

It seems like the KernelRng needs either an initial reseed call or
more random events added before the first call to get_good_random,
but I don't feel qualified to make that kind of change.
---
 Kernel/Arch/i386/CPU.cpp | 2 ++
 Kernel/Arch/i386/CPU.h   | 1 +
 Kernel/Random.cpp        | 2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Kernel/Arch/i386/CPU.cpp b/Kernel/Arch/i386/CPU.cpp
index 9ad0b6ff43..354447d5c5 100644
--- a/Kernel/Arch/i386/CPU.cpp
+++ b/Kernel/Arch/i386/CPU.cpp
@@ -714,6 +714,7 @@ bool g_cpu_supports_nx;
 bool g_cpu_supports_pae;
 bool g_cpu_supports_pge;
 bool g_cpu_supports_rdrand;
+bool g_cpu_supports_rdseed;
 bool g_cpu_supports_smap;
 bool g_cpu_supports_smep;
 bool g_cpu_supports_sse;
@@ -736,6 +737,7 @@ void cpu_detect()
     g_cpu_supports_smap = (extended_features.ebx() & (1 << 20));
     g_cpu_supports_smep = (extended_features.ebx() & (1 << 7));
     g_cpu_supports_umip = (extended_features.ecx() & (1 << 2));
+    g_cpu_supports_rdseed = (extended_features.ebx() & (1 << 18));
 }
 
 void cpu_setup()
diff --git a/Kernel/Arch/i386/CPU.h b/Kernel/Arch/i386/CPU.h
index b59819bc3f..398bbcd69d 100644
--- a/Kernel/Arch/i386/CPU.h
+++ b/Kernel/Arch/i386/CPU.h
@@ -588,6 +588,7 @@ extern bool g_cpu_supports_nx;
 extern bool g_cpu_supports_pae;
 extern bool g_cpu_supports_pge;
 extern bool g_cpu_supports_rdrand;
+extern bool g_cpu_supports_rdseed;
 extern bool g_cpu_supports_smap;
 extern bool g_cpu_supports_smep;
 extern bool g_cpu_supports_sse;
diff --git a/Kernel/Random.cpp b/Kernel/Random.cpp
index 93a84b7227..788c592080 100644
--- a/Kernel/Random.cpp
+++ b/Kernel/Random.cpp
@@ -44,7 +44,7 @@ KernelRng& KernelRng::the()
 
 KernelRng::KernelRng()
 {
-    if (g_cpu_supports_rdrand) {
+    if (g_cpu_supports_rdseed) {
         for (size_t i = 0; i < resource().pool_count * resource().reseed_threshold; ++i) {
             u32 value = 0;
             asm volatile(