Merge pull request #47 from surajssd/hash-extraction-api

vtpm: Add support to include PCR values

.gitignore

@@ -0,0 +1 @@
+.vscode

az-cvm-vtpm/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "az-cvm-vtpm"
-version = "0.4.1"
+version = "0.5.0"
 edition = "2021"
 repository = "https://github.com/kinvolk/azure-cvm-tooling/"
 license = "MIT"
@@ -12,7 +12,7 @@ description = "Package with shared code for Azure Confidential VMs"
 members = [
 	"az-snp-vtpm",
 	"az-tdx-vtpm",
-    "az-snp-vtpm/example",
+	"az-snp-vtpm/example",
 ]
 
 [lib]

az-cvm-vtpm/az-snp-vtpm/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "az-snp-vtpm"
-version = "0.4.1"
+version = "0.5.0"
 edition = "2021"
 repository = "https://github.com/kinvolk/azure-cvm-tooling/"
 license = "MIT"
@@ -17,7 +17,7 @@ path = "src/main.rs"
 required-features = ["attester", "verifier"]
 
 [dependencies]
-az-cvm-vtpm = { path = "..", version = "0.4.1" }
+az-cvm-vtpm = { path = "..", version = "0.5.0" }
 bincode.workspace = true
 clap.workspace = true
 openssl = { workspace = true, optional = true }

az-cvm-vtpm/az-snp-vtpm/src/main.rs

@@ -74,7 +74,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         Action::Quote { nonce } => {
             println!("quote byte size: {}", nonce.as_bytes().len());
             let quote = vtpm::get_quote(nonce.as_bytes())?;
-            println!("{:02X?}", quote.message);
+            println!("{:02X?}", quote.message());
         }
     }
 

az-cvm-vtpm/az-tdx-vtpm/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "az-tdx-vtpm"
-version = "0.4.1"
+version = "0.5.0"
 edition = "2021"
 repository = "https://github.com/kinvolk/azure-cvm-tooling/"
 license = "MIT"
@@ -16,7 +16,7 @@ name = "tdx-vtpm"
 path = "src/main.rs"
 
 [dependencies]
-az-cvm-vtpm = { path = "..", version = "0.4.1" }
+az-cvm-vtpm = { path = "..", version = "0.5.0" }
 base64-url = "2.0.0"
 bincode.workspace = true
 serde.workspace = true

az-cvm-vtpm/src/vtpm/mod.rs

@@ -5,6 +5,7 @@ use rsa::{BigUint, RsaPublicKey};
 use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use tss_esapi::abstraction::nv;
+use tss_esapi::abstraction::pcr;
 use tss_esapi::abstraction::public::DecodedKey;
 use tss_esapi::handles::TpmHandle;
 use tss_esapi::interface_types::algorithm::HashingAlgorithm;
@@ -101,6 +102,7 @@ pub fn get_ak_pub() -> Result<RsaPublicKey, AKPubError> {
     Ok(pkey)
 }
 
+#[non_exhaustive]
 #[derive(Error, Debug)]
 pub enum QuoteError {
     #[error("tpm error")]
@@ -111,12 +113,17 @@ pub enum QuoteError {
     NotAQuote,
     #[error("Wrong signature, that should not occur")]
     WrongSignature,
+    #[error("PCR bank not found")]
+    PcrBankNotFound,
+    #[error("PCR reading error")]
+    PcrRead,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone)]
 pub struct Quote {
-    pub signature: Vec<u8>,
-    pub message: Vec<u8>,
+    signature: Vec<u8>,
+    message: Vec<u8>,
+    pcrs: Vec<Vec<u8>>,
 }
 
 impl Quote {
@@ -126,6 +133,11 @@ impl Quote {
         let nonce = attest.extra_data().to_vec();
         Ok(nonce)
     }
+
+    /// Extract message from a Quote
+    pub fn message(&self) -> Vec<u8> {
+        self.message.clone()
+    }
 }
 
 /// Get a signed vTPM Quote
@@ -152,8 +164,12 @@ pub fn get_quote(data: &[u8]) -> Result<Quote, QuoteError> {
     let auth_session = AuthSession::Password;
     context.set_sessions((Some(auth_session), None, None));
 
-    let (attest, signature) =
-        context.quote(key_handle.into(), quote_data, scheme, selection_list)?;
+    let (attest, signature) = context.quote(
+        key_handle.into(),
+        quote_data,
+        scheme,
+        selection_list.clone(),
+    )?;
 
     let AttestInfo::Quote { .. } = attest.attested() else {
         return Err(QuoteError::NotAQuote);
@@ -165,18 +181,21 @@ pub fn get_quote(data: &[u8]) -> Result<Quote, QuoteError> {
     let signature = rsa_sig.signature().to_vec();
     let message = attest.marshall()?;
 
-    Ok(Quote { signature, message })
-}
+    context.clear_sessions();
+    let pcr_data = pcr::read_all(&mut context, selection_list)?;
 
-#[cfg(feature = "verifier")]
-#[derive(Error, Debug)]
-pub enum VerifyError {
-    #[error("tss error")]
-    Tss(#[from] tss_esapi::Error),
-    #[error("openssl error")]
-    OpenSsl(#[from] openssl::error::ErrorStack),
-    #[error("nonce mismatch")]
-    NonceMismatch,
-    #[error("quote is not signed by the public key")]
-    SignatureMismatch,
+    let pcr_bank = pcr_data
+        .pcr_bank(hash_algo)
+        .ok_or(QuoteError::PcrBankNotFound)?;
+
+    let pcrs = pcr_bank
+        .into_iter()
+        .map(|(_, x)| x.value().to_vec())
+        .collect();
+
+    Ok(Quote {
+        signature,
+        message,
+        pcrs,
+    })
 }

az-cvm-vtpm/src/vtpm/verify.rs

@@ -5,8 +5,12 @@ use super::{Quote, QuoteError};
 use openssl::hash::MessageDigest;
 use openssl::pkey::{PKey, Public};
 use openssl::sign::Verifier;
+use sha2::{Digest, Sha256};
 use thiserror::Error;
+use tss_esapi::structures::{Attest, AttestInfo};
+use tss_esapi::traits::UnMarshall;
 
+#[non_exhaustive]
 #[derive(Error, Debug)]
 pub enum VerifyError {
     #[error("tss error")]
@@ -19,6 +23,8 @@ pub enum VerifyError {
     NonceMismatch,
     #[error("quote error")]
     Quote(#[from] QuoteError),
+    #[error("pcr mismatch")]
+    PcrMismatch,
 }
 
 impl Quote {
@@ -36,6 +42,9 @@ impl Quote {
         if nonce != quote_nonce {
             return Err(VerifyError::NonceMismatch);
         }
+
+        self.verify_pcrs()?;
+
         Ok(())
     }
 
@@ -53,29 +62,78 @@ impl Quote {
         }
         Ok(())
     }
+
+    /// Verify that the TPM Quote's PCR digest matches the digest of the bundled PCR values
+    ///
+    pub fn verify_pcrs(&self) -> Result<(), VerifyError> {
+        let attest = Attest::unmarshall(&self.message)?;
+        let AttestInfo::Quote { info } = attest.attested() else {
+            return Err(VerifyError::Quote(QuoteError::NotAQuote));
+        };
+
+        let pcr_digest = info.pcr_digest();
+
+        // Read hashes of all the PCRs.
+        let mut hasher = Sha256::new();
+        for pcr in self.pcrs.iter() {
+            hasher.update(pcr);
+        }
+
+        let digest = hasher.finalize();
+        if digest[..] != pcr_digest[..] {
+            return Err(VerifyError::PcrMismatch);
+        }
+
+        Ok(())
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    // // Use this code to generate the scriptures for the test on an AMD CVM.
+    //
+    // use az_snp_vtpm::vtpm;
+    // use bincode;
+    // use rsa;
+    // use rsa::pkcs8::EncodePublicKey;
+    // use std::error::Error;
+    // use std::fs;
+    //
+    // fn main() -> Result<(), Box<dyn Error>> {
+    //     // Extract the AK public key.
+    //     let foo = vtpm::get_ak_pub()?.to_public_key_pem(rsa::pkcs8::LineEnding::LF)?;
+    //     fs::write("/tmp/akpub.pem", foo)?;
+    //
+    //     // Save the PCRs into binary file.
+    //     let nonce = "challenge".as_bytes().to_vec();
+    //     let quote = vtpm::get_quote(&nonce)?;
+    //     let quote_encoded: Vec<u8> = bincode::serialize(&quote).unwrap();
+    //     fs::write("/tmp/quote.bin", quote_encoded)?;
+    //
+    //     Ok(())
+    // }
+
     #[cfg(feature = "verifier")]
     #[test]
     fn test_quote_validation() {
         // Can be retrieved by `get_ak_pub()` or via tpm2-tools:
-        // `tpm2_readpublic -c 0x81000003 -f pem -o akpub.pem`
-
+        // sudo tpm2_readpublic -c 0x81000003 -f pem -o akpub.pem
         let pem = include_bytes!("../../test/akpub.pem");
         let pkey = PKey::public_key_from_pem(pem).unwrap();
 
         // Can be retrieved by `get_quote()` or via tpm2-tools:
-        // `tpm2_quote -c 0x81000003 -l sha256:5,8 -q cafe -m quote_msg -s quote_sig`
-        let message = include_bytes!("../../test/quote_msg").to_vec();
-        let signature = include_bytes!("../../test/quote_sig").to_vec();
-        let quote = Quote { signature, message };
+        // For message and signature:
+        // sudo tpm2_quote -c 0x81000003 -l sha256:5,8 -q challenge -m quote_msg -s quote_sig
+        //
+        // For PCR values:
+        // sudo tpm2_pcrread sha256:0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23
+        let quote_bytes = include_bytes!("../../test/quote.bin");
+        let quote: Quote = bincode::deserialize(quote_bytes).unwrap();
 
         // proper nonce in message
-        let nonce = vec![1, 2, 3];
+        let nonce = "challenge".as_bytes().to_vec();
         let result = quote.verify(&pkey, &nonce);
         assert!(result.is_ok(), "Quote verification should not fail");
 
@@ -98,4 +156,12 @@ mod tests {
             "Expected nonce verification error"
         );
     }
+
+    #[test]
+    fn test_pcr_values() {
+        let quote_bytes = include_bytes!("../../test/quote.bin");
+        let quote: Quote = bincode::deserialize(quote_bytes).unwrap();
+        let result = quote.verify_pcrs();
+        assert!(result.is_ok(), "PCR verification should not fail");
+    }
 }

az-cvm-vtpm/test/akpub.pem

@@ -1,9 +1,9 @@
 -----BEGIN PUBLIC KEY-----
-MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAxfSaJAABoi7dSNwLgxab
-Qj0Ag+3u74ioHzP/JKk7urkxwFyPN95+ofKhBIp63mfOxTVIfjPFhiYhnYGKJvQY
-drTg1slNSIR5MRcjwDhHlTwK4BefiwcIiQMsEwdjbWEcHVfKIjrIFLX6HgXwftGU
-mdItDBJuZaGT08F1kGMz7K6hH1ZjQBKnwmGih5p/P4pBDD4ccNapUtaIraCgQ+4f
-YguTMACZAl7ZZxISS1yxxudHbJ8cI7viijk1TmuauJN+GAn7hkEauOdWd6xpv8jf
-NHEm24kTh/TgNhTlyZpfafEbwXNVNVk7TZ3HRNl0Uou4FNCQw8eb+PG3q/IxMv7h
-oQIDAQAB
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAxJlHggAAGWfX9uqSq3js
+wJ9PGrEGyurECyTMfptLwI5Ca1JEwocKXHsTfdAEUVIi9GVWcNuBGpr5Dbd8reoE
+l6/p5IoxQsXyPSC6LZ7HdisORYOo8tQU/fqcuRky1InLJnsKG0o91XEP1MBo5/J7
+MxUAkkWPOiA6wPo+k7Wo3X3TB1NxxqohqAN+sRQ3Useqlzg7sViw+us0nrPb5gbz
+1M8PMlLj4UW6j2j+XNQMsPtZEJ5qAwOmtqstFqT16qBkqFd/ey+NQBNINQAYlaHT
+Vh2cwzq17i2Cru0KSHGQVa2YcUPZhDu4eAQdy+fdVE/uTjxf7Sac5WXefK2YXxyw
+VQIDAQAB
 -----END PUBLIC KEY-----