It's considerably better than any of the alternatives on KVM.
Signed-off-by: Andy Lutomirski <l...@amacapital.net>
---
arch/x86/boot/compressed/aslr.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index fc6091a..8583f0e 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -5,6 +5,8 @@
#include <asm/archrandom.h>
#include <asm/e820.h>
+#include <uapi/asm/kvm_para.h>
+
#include <generated/compile.h>
#include <linux/module.h>
#include <linux/uts.h>
@@ -15,6 +17,22 @@
static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
+static bool kvm_para_has_feature(unsigned int feature)
+{
+ u32 kvm_base;
+ u32 features;
+
+ if (!has_cpuflag(X86_FEATURE_HYPERVISOR))
+ return false;
+
+ kvm_base = hypervisor_cpuid_base("KVMKVMKVM\0\0\0", KVM_CPUID_FEATURES);
+ if (!kvm_base)
+ return false;
+
+ features = cpuid_eax(kvm_base | KVM_CPUID_FEATURES);
+ return features & (1UL << feature);
+}
+
#define I8254_PORT_CONTROL 0x43
#define I8254_PORT_COUNTER0 0x40
#define I8254_CMD_READBACK 0xC0
@@ -81,6 +99,15 @@ static unsigned long get_random_long(void)
}
}
+ if (kvm_para_has_feature(KVM_FEATURE_GET_RNG_SEED)) {
+ u64 seed;
+
+ debug_putstr(" MSR_KVM_GET_RNG_SEED");
+ rdmsrl(MSR_KVM_GET_RNG_SEED, seed);
+ random ^= (unsigned long)seed;
+ use_i8254 = false;
+ }
+
if (has_cpuflag(X86_FEATURE_TSC)) {
debug_putstr(" RDTSC");
rdtscll(raw);
--
1.9.3
--
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