From: Michael Brown <mcb30@ipxe.org>
Date: Wed, 12 May 2021 09:24:00 +0000 (+0100)
Subject: [rng] Check for TSC support before using RTC entropy source
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=05fcf1a2f0809b8d87ca5affea1f1bfe0996235b;p=thirdparty%2Fipxe.git

[rng] Check for TSC support before using RTC entropy source

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---

diff --git a/src/arch/x86/include/ipxe/cpuid.h b/src/arch/x86/include/ipxe/cpuid.h
index b5403bd9d..3983dfb89 100644
--- a/src/arch/x86/include/ipxe/cpuid.h
+++ b/src/arch/x86/include/ipxe/cpuid.h
@@ -42,6 +42,9 @@ struct x86_features {
 /** Hypervisor is present */
 #define CPUID_FEATURES_INTEL_ECX_HYPERVISOR 0x80000000UL
 
+/** TSC is present */
+#define CPUID_FEATURES_INTEL_EDX_TSC 0x00000010UL
+
 /** FXSAVE and FXRSTOR are supported */
 #define CPUID_FEATURES_INTEL_EDX_FXSR 0x01000000UL
 
diff --git a/src/arch/x86/interface/pcbios/rtc_entropy.c b/src/arch/x86/interface/pcbios/rtc_entropy.c
index e9e6baa59..e0c175685 100644
--- a/src/arch/x86/interface/pcbios/rtc_entropy.c
+++ b/src/arch/x86/interface/pcbios/rtc_entropy.c
@@ -36,6 +36,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <biosint.h>
 #include <pic8259.h>
 #include <rtc.h>
+#include <ipxe/cpuid.h>
 #include <ipxe/entropy.h>
 
 /** Maximum time to wait for an RTC interrupt, in milliseconds */
@@ -174,8 +175,17 @@ static int rtc_entropy_check ( void ) {
  * @ret rc		Return status code
  */
 static int rtc_entropy_enable ( void ) {
+	struct x86_features features;
 	int rc;
 
+	/* Check that TSC is supported */
+	x86_features ( &features );
+	if ( ! ( features.intel.edx & CPUID_FEATURES_INTEL_EDX_TSC ) ) {
+		DBGC ( &rtc_flag, "RTC has no TSC\n" );
+		rc = -ENOTSUP;
+		goto err_no_tsc;
+	}
+
 	/* Hook ISR and enable RTC interrupts */
 	rtc_hook_isr();
 	enable_irq ( RTC_IRQ );
@@ -191,6 +201,7 @@ static int rtc_entropy_enable ( void ) {
 	rtc_disable_int();
 	disable_irq ( RTC_IRQ );
 	rtc_unhook_isr();
+ err_no_tsc:
 	return rc;
 }