commit 8edf72eafa4b1f4aa5c726a0573b6c2e18b49543
author Pierre-Clément Tosi <ptosi@google.com> Tue Dec 06 16:02:57 2022 +0000
committer Pierre-Clément Tosi <ptosi@google.com> Thu Dec 08 16:29:12 2022 +0000
tree 338cb1bf33c84467294ba691851ff9c4a1b43a28
parent db14ada78bdfceac6f1a566815881d04c5f760c3

pvmfw: Validate input BCC handover

Ensure that the BCC contained in the configuration data is properly
formatted as a "BCC Handover" [1] i.e. a CBOR-encoded map

    BccHandover = {
      1 : bstr .size 32,     ; CDI_Attest
      2 : bstr .size 32,     ; CDI_Seal
      3 : Bcc,               ; Certificate chain
    }

If not, abort the pVM boot.

[1]: https://pigweed.googlesource.com/open-dice/+/72ad792c4d9ffffef3412801b5da46568a6b3197/src/android/bcc.c#260

Bug: 256827715
Test: atest MicrodroidHostTests
Change-Id: Ibade0ebd1e50d912a59b32c1282022aa46235501

pvmfw/src/entry.rs

diff --git a/pvmfw/src/entry.rs b/pvmfw/src/entry.rs
index e8f9bb2..bffc140 100644
--- a/pvmfw/src/entry.rs
+++ b/pvmfw/src/entry.rs
@@ -24,6 +24,7 @@
 use core::arch::asm;
 use core::num::NonZeroUsize;
 use core::slice;
+use dice::bcc::Handover;
 use log::debug;
 use log::error;
 use log::info;
@@ -228,8 +229,9 @@
         RebootReason::InvalidConfig
     })?;
 
-    let bcc = appended.get_bcc_mut().ok_or_else(|| {
-        error!("Invalid BCC");
+    let bcc_slice = appended.get_bcc_mut();
+    let bcc = Handover::new(bcc_slice).map_err(|e| {
+        error!("Invalid BCC Handover: {e:?}");
         RebootReason::InvalidBcc
     })?;
 
@@ -243,7 +245,7 @@
     let slices = MemorySlices::new(fdt, payload, payload_size, &mut memory)?;
 
     // This wrapper allows main() to be blissfully ignorant of platform details.
-    crate::main(slices.fdt, slices.kernel, slices.ramdisk, bcc, &mut memory)?;
+    crate::main(slices.fdt, slices.kernel, slices.ramdisk, &bcc, &mut memory)?;
 
     // TODO: Overwrite BCC before jumping to payload to avoid leaking our sealing key.
 
@@ -366,12 +368,10 @@
         }
     }
 
-    fn get_bcc_mut(&mut self) -> Option<&mut [u8]> {
-        let bcc = match self {
+    fn get_bcc_mut(&mut self) -> &mut [u8] {
+        match self {
             Self::LegacyBcc(ref mut bcc) => bcc,
             Self::Config(ref mut cfg) => cfg.get_bcc_mut(),
-        };
-        // TODO(b/256148034): return None if BccHandoverParse(bcc) != kDiceResultOk.
-        Some(bcc)
+        }
     }
 }