Combine PRK and IDK_S generation VTL calls

dev_tests/src/ratchet.rs

@@ -37,7 +37,7 @@ fn ratchet_globals() -> Result<()> {
             ("litebox/", 9),
             ("litebox_platform_linux_kernel/", 6),
             ("litebox_platform_linux_userland/", 5),
-            ("litebox_platform_lvbs/", 23),
+            ("litebox_platform_lvbs/", 24),
             ("litebox_platform_multiplex/", 1),
             ("litebox_platform_windows_userland/", 8),
             ("litebox_runner_lvbs/", 6),

litebox_common_lvbs/src/lib.rs

@@ -27,6 +27,9 @@ pub const PAGE_SHIFT: usize = 12;
 /// Length of the Platform Root Key in bytes.
 pub const PRK_LEN: usize = 32;
 
+/// Length of the CRNG seed.
+pub const CRNG_SEED_LEN: usize = 32;
+
 /// Maximum number of CPU cores addressable through the VTL0 `cpu_online_mask`
 /// ABI. Bounds how many bits of the mask VTL1 will honor when booting APs.
 pub const MAX_CORES: usize = 128;
@@ -48,11 +51,8 @@ pub const VSM_VTL_CALL_FUNC_ID_KEXEC_VALIDATE: u32 = 0x1_ffea;
 pub const VSM_VTL_CALL_FUNC_ID_PATCH_TEXT: u32 = 0x1_ffeb;
 pub const VSM_VTL_CALL_FUNC_ID_ALLOCATE_RINGBUFFER_MEMORY: u32 = 0x1_ffec;
 
-// This VSM function ID for setting the platform root key is subject to change
-pub const VSM_VTL_CALL_FUNC_ID_SET_PLATFORM_ROOT_KEY: u32 = 0x1_ffed;
-
-// This VSM function ID for generating the identity signing key is subject to change
-pub const VSM_VTL_CALL_FUNC_ID_GENERATE_IDENTITY_SIGNING_KEY: u32 = 0x1_ffee;
+// This VSM function ID for exchanging secrets is subject to change
+pub const VSM_VTL_CALL_FUNC_ID_EXCHANGE_SECRETS: u32 = 0x1_ffed;
 
 // This VSM function ID for OP-TEE messages is subject to change
 pub const VSM_VTL_CALL_FUNC_ID_OPTEE_MESSAGE: u32 = 0x1_fff0;
@@ -76,8 +76,7 @@ pub enum VsmFunction {
     PatchText = VSM_VTL_CALL_FUNC_ID_PATCH_TEXT,
     OpteeMessage = VSM_VTL_CALL_FUNC_ID_OPTEE_MESSAGE,
     AllocateRingbufferMemory = VSM_VTL_CALL_FUNC_ID_ALLOCATE_RINGBUFFER_MEMORY,
-    SetPlatformRootKey = VSM_VTL_CALL_FUNC_ID_SET_PLATFORM_ROOT_KEY,
-    GenerateIdentitySigningKey = VSM_VTL_CALL_FUNC_ID_GENERATE_IDENTITY_SIGNING_KEY,
+    ExchangeSecrets = VSM_VTL_CALL_FUNC_ID_EXCHANGE_SECRETS,
 }
 
 // `HV_STATUS_*` constants used as discriminants for `HypervCallError`.
@@ -970,6 +969,9 @@ pub trait Vtl1Gate {
     /// Read the platform root key from VTL0 `key_pa` and store it in VTL1 state.
     fn set_platform_root_key(&self, key_pa: u64) -> Result<(), VsmError>;
 
+    /// Read a CRNG seed from VTL0 `trusted_seed_pa` and store it in VTL1.
+    fn set_crng_seed(&self, trusted_seed_pa: u64) -> Result<(), VsmError>;
+
     /// Close VTL1's window of trusting VTL0, making
     /// [`Vtl0Gate::end_of_boot_reached`] report `true` from here on. One-way:
     /// the window never reopens.

litebox_platform_lvbs/src/host/lvbs_impl.rs

@@ -8,7 +8,7 @@ use crate::{
     host::per_cpu_variables::with_per_cpu_variables,
 };
 use digest::Digest;
-use litebox_common_lvbs::PRK_LEN;
+use litebox_common_lvbs::{CRNG_SEED_LEN, PRK_LEN};
 use rand_core::{RngCore, SeedableRng};
 use zeroize::Zeroizing;
 
@@ -112,7 +112,7 @@ impl litebox::platform::CrngProvider for LvbsLinuxKernel {
         random
             .get_or_insert_with(|| {
                 LvbsCrng::new(
-                    PRK_ONCE.get().expect("Platform root key not initialized"),
+                    CRNG_SEED_ONCE.get().expect("CRNG seed not set"),
                     rdrand_seed().expect("RDRAND unavailable during CRNG initialization"),
                 )
             })
@@ -134,10 +134,10 @@ struct LvbsCrng {
 }
 
 impl LvbsCrng {
-    fn new(prk: &[u8; PRK_LEN], rdrand_seed: CrngSeed) -> Self {
+    fn new(seed: &[u8; CRNG_SEED_LEN], rdrand_seed: CrngSeed) -> Self {
         Self {
-            random: rand_chacha::ChaCha20Rng::from_seed(crng_seed_from_prk_and_rdrand(
-                prk,
+            random: rand_chacha::ChaCha20Rng::from_seed(crng_seed_from_rot_and_rdrand(
+                seed,
                 rdrand_seed,
             )),
             bytes_until_reseed: CRNG_RESEED_INTERVAL_BYTES,
@@ -176,6 +176,7 @@ impl LvbsCrng {
 }
 
 static PRK_ONCE: spin::Once<[u8; PRK_LEN]> = spin::Once::new();
+static CRNG_SEED_ONCE: spin::Once<[u8; CRNG_SEED_LEN]> = spin::Once::new();
 
 // Do not expose a raw PRK getter (i.e., no `get_platform_root_key`).
 // Consumers should provide key derivation function and context
@@ -193,6 +194,18 @@ pub(crate) fn set_platform_root_key(key: &[u8; PRK_LEN]) {
     });
 }
 
+/// Sets the trusted CRNG seed for this platform.
+///
+/// This should be called once during platform initialization with a seed
+/// derived from a hardware root of trust (e.g., a TPM).
+pub(crate) fn set_crng_seed(seed: &[u8; CRNG_SEED_LEN]) {
+    CRNG_SEED_ONCE.call_once(|| {
+        let mut s = Zeroizing::new([0u8; CRNG_SEED_LEN]);
+        s.copy_from_slice(seed);
+        *s
+    });
+}
+
 impl litebox::platform::DerivedKeyProvider for LvbsLinuxKernel {
     fn derive_key<E>(
         &self,
@@ -231,10 +244,10 @@ fn rdrand_seed() -> Option<CrngSeed> {
     Some(seed)
 }
 
-fn crng_seed_from_prk_and_rdrand(prk: &[u8; PRK_LEN], rdrand_seed: CrngSeed) -> CrngSeed {
+fn crng_seed_from_rot_and_rdrand(seed: &[u8; CRNG_SEED_LEN], rdrand_seed: CrngSeed) -> CrngSeed {
     sha2::Sha256::new()
         .chain_update(b"litebox-lvbs-crng-seed-v1")
-        .chain_update(prk)
+        .chain_update(seed)
         .chain_update(rdrand_seed)
         .finalize()
         .into()

litebox_platform_lvbs/src/host/mod.rs

@@ -8,7 +8,7 @@ pub mod lvbs_impl;
 pub mod per_cpu_variables;
 
 pub use lvbs_impl::LvbsLinuxKernel;
-pub(crate) use lvbs_impl::set_platform_root_key;
+pub(crate) use lvbs_impl::{set_crng_seed, set_platform_root_key};
 
 #[cfg(test)]
 pub mod mock;

litebox_platform_lvbs/src/mshv/vsm.rs

@@ -27,8 +27,8 @@ use core::ops::Range;
 use litebox::utils::TruncateExt;
 use litebox_common_linux::vmap::PhysPageAddr;
 use litebox_common_lvbs::{
-    FrameTxn, HypervCallError, MemAttr, PAGE_SHIFT, PAGE_SIZE, PRK_LEN, ReservationStatus,
-    VsmError, Vtl0Gate, Vtl0PrivilegedWrite, Vtl1Gate,
+    CRNG_SEED_LEN, FrameTxn, HypervCallError, MemAttr, PAGE_SHIFT, PAGE_SIZE, PRK_LEN,
+    ReservationStatus, VsmError, Vtl0Gate, Vtl0PrivilegedWrite, Vtl1Gate,
 };
 use rangemap::RangeSet;
 use spin::{Once, rwlock::RwLock as SpinRwLock};
@@ -790,4 +790,18 @@ impl Vtl1Gate for LvbsVtl1Gate {
         crate::host::set_platform_root_key(&keybuf);
         Ok(())
     }
+
+    fn set_crng_seed(&self, seed_pa: u64) -> Result<(), VsmError> {
+        if crate::platform_low().end_of_boot_reached() {
+            return Err(VsmError::OperationAfterEndOfBoot("set crng seed"));
+        }
+
+        let seed_pa = PhysAddr::try_new(seed_pa).map_err(|_| VsmError::InvalidPhysicalAddress)?;
+        let mut seed = Zeroizing::new([0u8; CRNG_SEED_LEN]);
+        LvbsVtl0Gate::mint()
+            .read_vtl0_contiguous(seed_pa.as_u64(), &mut *seed)
+            .map_err(|_| VsmError::Vtl0CopyFailed)?;
+        crate::host::set_crng_seed(&seed);
+        Ok(())
+    }
 }

litebox_runner_lvbs/src/lib.rs

@@ -13,7 +13,7 @@ use litebox::{
     utils::{ReinterpretSignedExt, TruncateExt},
 };
 use litebox_common_linux::errno::Errno;
-use litebox_common_lvbs::{NUM_VTLCALL_PARAMS, VsmError, VsmFunction};
+use litebox_common_lvbs::{NUM_VTLCALL_PARAMS, PRK_LEN, VsmError, VsmFunction};
 use litebox_common_optee::{
     OpteeMessageCommand, OpteeMsgArgs, OpteeRpcArgs, OpteeSmcArgs, OpteeSmcResult,
     OpteeSmcReturnCode, TeeOrigin, TeeResult, UteeEntryFunc, UteeParams, optee_msg_args_total_size,
@@ -261,9 +261,15 @@ fn vtlcall_dispatch(params: &[u64; NUM_VTLCALL_PARAMS]) -> i64 {
             let smc_args_pfn = params[1];
             optee_smc_handler_entry(smc_args_pfn)
         }
-        VsmFunction::GenerateIdentitySigningKey => {
-            let public_key_pa = params[1];
-            let key_alg = params[2];
+        VsmFunction::ExchangeSecrets => {
+            let public_key_pa = params[2];
+            let key_alg = params[3];
+
+            let return_code = vsm_dispatch(VsmFunction::ExchangeSecrets, &params[1..2]);
+            if return_code < 0 {
+                return return_code;
+            }
+
             litebox_shim_optee::idk::generate_identity_signing_key(public_key_pa, key_alg)
         }
         _ => vsm_dispatch(func_id, &params[1..]),
@@ -315,10 +321,15 @@ fn vsm_dispatch(func_id: VsmFunction, params: &[u64]) -> i64 {
         VsmFunction::AllocateRingbufferMemory => {
             heki.allocate_ringbuffer_memory(params[0], params[1])
         }
-        VsmFunction::SetPlatformRootKey => vtl1.set_platform_root_key(params[0]).map(|()| 0),
-        VsmFunction::GenerateIdentitySigningKey => {
-            Err(VsmError::OperationNotSupported("Identity key generation"))
-        }
+        VsmFunction::ExchangeSecrets => vtl1
+            .set_platform_root_key(params[0])
+            .and_then(|()| {
+                params[0]
+                    .checked_add(PRK_LEN as u64)
+                    .ok_or(VsmError::IntegerOverflow)
+            })
+            .and_then(|crng_seed_pa| vtl1.set_crng_seed(crng_seed_pa))
+            .map(|()| 0),
         VsmFunction::OpteeMessage => Err(VsmError::OperationNotSupported("OP-TEE communication")),
     };
     match result {