Use SYSFS to read MSR_SEV_STATUS

src/ok.rs

@@ -1,6 +1,8 @@
 use super::*;
 
 use std::fmt;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
 
 use bitfield::bitfield;
 use colorful::*;
@@ -10,6 +12,9 @@ use serde::{Deserialize, Serialize};
 const SEV_MASK: usize = 1;
 const ES_MASK: usize = 1 << 1;
 const SNP_MASK: usize = 1 << 2;
+const MSR_SEV_STATUS: u32 = 0xC0010131;
+const SEV_STATUS_SYSFS_FILENAME: &str = "/sys/devices/system/cpu/sev/sev_status";
+
 type TestFn = dyn Fn() -> TestResult;
 
 struct Test {
@@ -71,12 +76,12 @@ impl fmt::Display for TestState {
 }
 
 fn collect_tests() -> Vec<Test> {
-    // Grab your MSR value one time.
-    let temp_bitfield = match get_values(0xC0010131, 0) {
+    // Grab SEV_STATUS one time.
+    let temp_bitfield = match get_sev_status() {
         Ok(temp_bitfield) => temp_bitfield,
         Err(e) => {
             return vec![Test {
-                name: "Error reading MSR",
+                name: "Error reading SEV_STATUS",
                 gen_mask: SEV_MASK,
                 run: Box::new(move || TestResult {
                     name: "Error reading MSR".to_string(),
@@ -345,12 +350,25 @@ fn emit_skip(tests: &[Test], level: usize, quiet: bool) {
     }
 }
 
-fn get_values(reg: u32, cpu: u16) -> Result<SevStatus, anyhow::Error> {
-    let mut msr = Msr::new(reg, cpu).context("Error Reading MSR")?;
+fn get_status_sysfs() -> Result<SevStatus, anyhow::Error> {
+    let status_file = File::open(SEV_STATUS_SYSFS_FILENAME)?;
+    let mut reader = BufReader::new(status_file);
+    let mut buffer = String::new();
+
+    reader.read_line(&mut buffer)?;
+    Ok(SevStatus(u64::from_str_radix(buffer.trim(), 16)?))
+}
+
+fn get_status_msr() -> Result<SevStatus, anyhow::Error> {
+    let mut msr = Msr::new(MSR_SEV_STATUS, 0).context("Error Reading MSR")?;
     let my_bitfield = SevStatus(msr.read()?);
     Ok(my_bitfield)
 }
 
+fn get_sev_status() -> Result<SevStatus, anyhow::Error> {
+    get_status_sysfs().or_else(|_| get_status_msr())
+}
+
 fn run_msr_check(check_bit: u64, sev_feature: &str, optional_field: bool) -> TestResult {
     let mut status = TestState::Fail;
     let mut message = "DISABLED".to_string();