feat: Hook up check_sig host function

crates/xrpl-host-functions/src/lib.rs

@@ -217,6 +217,23 @@ host_functions! {
     #[wasm_name = "le_inner_arr_len"]
     fn get_ledger_obj_nested_array_len(&self, cache_idx: i32, locator: &[u8]) -> HostResult<i32>;
 
+    /// Verify `signature` over `message` under `pubkey`. Reads the three regions and
+    /// answers `1` if the signature is valid, `0` if not, or a negative error.
+    ///
+    /// GAS DISCREPANCY: this 300 is the value the C-ABI fork registered
+    /// (`rippled-wasm-host-functions`, WasmVM.cpp), which this port follows. The
+    /// prior C++ integration in this tree charged 35000 for the same call — 100x
+    /// more, and closer to the real cost of signature verification. The value is
+    /// consensus-critical, so confirm which is intended before this ships.
+    #[gas = 300]
+    #[wasm_name = "check_sig"]
+    fn check_signature(
+        &self,
+        message: &[u8],
+        signature: &[u8],
+        pubkey: &[u8],
+    ) -> HostResult<i32>;
+
     /// The XRPL `sha512Half` of `data`: the first [`HASH_LEN`] bytes of its SHA-512.
     #[gas = 2000]
     #[wasm_name = "sha512_half"]

crates/xrpl-host-functions/tests/generated_abi.rs

@@ -163,6 +163,16 @@ impl HostFunctions for FakeHost {
         Ok(cache_idx + locator.len() as i32)
     }
 
+    /// Reads three regions and returns a verdict: valid unless the signature is empty.
+    fn check_signature(
+        &self,
+        _message: &[u8],
+        signature: &[u8],
+        _pubkey: &[u8],
+    ) -> HostResult<i32> {
+        Ok(i32::from(!signature.is_empty()))
+    }
+
     fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
         let mut digest = [0; HASH_LEN];
         digest[0] = data.len() as u8;
@@ -247,6 +257,8 @@ fn the_trait_is_implementable() {
         host.get_ledger_obj_nested_array_len(0, &[9, 0, 0, 0]),
         Err(HostError::LocatorMalformed)
     );
+    assert_eq!(host.check_signature(b"msg", b"sig", b"pk"), Ok(1));
+    assert_eq!(host.check_signature(b"msg", b"", b"pk"), Ok(0));
     assert_eq!(host.sha512_half(b"abc", &mut out), Ok(HASH_LEN));
     assert_eq!(out[0], 3);
     assert_eq!(host.trace("hello", b"xy", true), Ok(()));
@@ -332,6 +344,7 @@ fn the_spec_table_matches_the_declarations() {
             ("tx_inner_arr_len", 70),
             ("home_le_inner_arr_len", 70),
             ("le_inner_arr_len", 70),
+            ("check_sig", 300),
             ("sha512_half", 2000),
             ("trace", 500),
             ("trace_num", 500),

crates/xrpl-wasm-vm-ffi/src/lib.rs

@@ -250,6 +250,16 @@ mod ffi {
             locator: &[u8],
         ) -> i32;
 
+        /// Answers `1`/`0` for a valid/invalid signature, or a negative `HostError`.
+        #[namespace = "xrpl"]
+        #[cxx_name = "checkSignature"]
+        fn check_signature(
+            self: &HostContext,
+            message: &[u8],
+            signature: &[u8],
+            pubkey: &[u8],
+        ) -> i32;
+
         #[namespace = "xrpl"]
         #[cxx_name = "sha512Half"]
         fn sha512_half(self: &HostContext, data: &[u8], out: &mut [u8]) -> i32;
@@ -393,6 +403,10 @@ impl HostFunctions for CxxHost<'_> {
         scalar(self.ctx.get_ledger_obj_nested_array_len(cache_idx, locator))
     }
 
+    fn check_signature(&self, message: &[u8], signature: &[u8], pubkey: &[u8]) -> HostResult<i32> {
+        scalar(self.ctx.check_signature(message, signature, pubkey))
+    }
+
     fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
         bytes_written(self.ctx.sha512_half(data, out))
     }

crates/xrpl-wasm-vm/src/abi.rs

@@ -257,6 +257,14 @@ mod tests {
         ) -> HostResult<i32> {
             unreachable!("no unit test in this module calls the host")
         }
+        fn check_signature(
+            &self,
+            _message: &[u8],
+            _signature: &[u8],
+            _pubkey: &[u8],
+        ) -> HostResult<i32> {
+            unreachable!("no unit test in this module calls the host")
+        }
         fn sha512_half(&self, _data: &[u8], _out: &mut [u8]) -> HostResult<usize> {
             unreachable!("no unit test in this module calls the host")
         }

crates/xrpl-wasm-vm/src/register.rs

@@ -304,6 +304,26 @@ pub(crate) fn register_host_functions(
                     )
                 },
             ),
+            HostFunctionSpec::CheckSignature => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 msg_ptr: i32,
+                 msg_len: i32,
+                 sig_ptr: i32,
+                 sig_len: i32,
+                 pk_ptr: i32,
+                 pk_len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(&mut caller, HostFunctionSpec::CheckSignature, |c| {
+                        let host = c.data().host;
+                        let message = read_borrowed(c, Region::new(msg_ptr, msg_len))?;
+                        let signature = read_borrowed(c, Region::new(sig_ptr, sig_len))?;
+                        let pubkey = read_borrowed(c, Region::new(pk_ptr, pk_len))?;
+                        host.check_signature(message, signature, pubkey)
+                    })
+                },
+            ),
             HostFunctionSpec::Sha512Half => linker.func_wrap(
                 HOST_MODULE,
                 op.wasm_name(),

crates/xrpl-wasm-vm/tests/budgets.rs

@@ -139,6 +139,11 @@ fn call_for(op: HostFunctionSpec) -> Call {
             "(call $le_inner_arr_len (i32.const 1) (i32.const 0) (i32.const 4))",
             3,
         ),
+        HostFunctionSpec::CheckSignature => (
+            import::CHECK_SIG,
+            "(call $check_sig (i32.const 0) (i32.const 0) (i32.const 0) (i32.const 0) (i32.const 0) (i32.const 0))",
+            6,
+        ),
         HostFunctionSpec::Sha512Half => (
             import::SHA512_HALF,
             "(call $sha512_half (i32.const 0) (i32.const 4) (i32.const 0) (i32.const 32))",

crates/xrpl-wasm-vm/tests/host_calls.rs

@@ -333,6 +333,32 @@ fn le_inner_arr_len_reads_the_slot_and_locator_and_returns_the_count() {
     assert_eq!(*host.le_nested_arr_lens_asked.borrow(), vec![(3, locator)]);
 }
 
+/// A call that reads three input regions and returns a scalar verdict: the message,
+/// signature, and pubkey all reach the host, and the verdict comes back as the status.
+#[test]
+fn check_sig_reads_all_three_regions_and_returns_the_verdict() {
+    let host = FakeHost::new(); // valid by default
+
+    // message @0 len 3, signature @8 len 4, pubkey @16 len 5 — memory is zeroed.
+    let wat = module(
+        &[import::CHECK_SIG, ONE_PAGE],
+        "(call $check_sig
+            (i32.const 0) (i32.const 3)
+            (i32.const 8) (i32.const 4)
+            (i32.const 16) (i32.const 5))",
+    );
+    assert_eq!(status(&wat, &host), 1, "the valid verdict");
+    assert_eq!(
+        *host.sigs_checked.borrow(),
+        [(vec![0u8; 3], vec![0u8; 4], vec![0u8; 5])],
+        "the three regions reached the host at their declared lengths"
+    );
+
+    // An invalid signature comes back as 0 — a value, not an error.
+    let host = FakeHost::new().answering_check_sig(Ok(0));
+    assert_eq!(status(&wat, &host), 0, "the invalid verdict");
+}
+
 /// A leading scalar parameter reaches the host as declared.
 #[test]
 fn home_le_field_passes_the_field_selector_through() {

crates/xrpl-wasm-vm/tests/preflight.rs

@@ -98,7 +98,7 @@ fn a_disabled_feature_does_not_pass() {
 
 /// Every host function the ABI declares, spelled as a guest imports it. The count
 /// is asserted against the ABI so a function added to it cannot be left out here.
-const ALL_IMPORTS: [&str; 21] = [
+const ALL_IMPORTS: [&str; 22] = [
     import::LDGR_INDEX,
     import::PARENT_LDGR_TIME,
     import::PARENT_LDGR_HASH,
@@ -117,6 +117,7 @@ const ALL_IMPORTS: [&str; 21] = [
     import::TX_INNER_ARR_LEN,
     import::HOME_LE_INNER_ARR_LEN,
     import::LE_INNER_ARR_LEN,
+    import::CHECK_SIG,
     import::SHA512_HALF,
     import::TRACE,
     import::TRACE_NUM,

crates/xrpl-wasm-vm/tests/support/mod.rs

@@ -175,6 +175,10 @@ pub struct FakeHost {
     pub le_nested_arr_lens: HashMap<(i32, Vec<u8>), i32>,
     /// Every (cache slot, locator) `get_ledger_obj_nested_array_len` was asked for.
     pub le_nested_arr_lens_asked: RefCell<Vec<(i32, Vec<u8>)>>,
+    /// What `check_signature` answers, whatever it is given.
+    pub sig_valid: HostResult<i32>,
+    /// Every (message, signature, pubkey) `check_signature` was asked to verify.
+    pub sigs_checked: RefCell<Vec<(Vec<u8>, Vec<u8>, Vec<u8>)>>,
     /// What `sha512_half` answers, whatever it is given.
     pub digest: Answer,
     /// Every field selector `get_current_ledger_obj_field` was asked for.
@@ -226,6 +230,9 @@ impl Default for FakeHost {
             home_le_nested_arr_lens_asked: RefCell::new(Vec::new()),
             le_nested_arr_lens: HashMap::new(),
             le_nested_arr_lens_asked: RefCell::new(Vec::new()),
+            // Valid by default; the verification itself is the host's job, not the ABI's.
+            sig_valid: Ok(1),
+            sigs_checked: RefCell::new(Vec::new()),
             digest: Answer::filler(32),
             fields_asked: RefCell::new(Vec::new()),
             digested: RefCell::new(Vec::new()),
@@ -339,6 +346,11 @@ impl FakeHost {
         self
     }
 
+    pub fn answering_check_sig(mut self, answer: HostResult<i32>) -> FakeHost {
+        self.sig_valid = answer;
+        self
+    }
+
     pub fn answering_digest(mut self, answer: Answer) -> FakeHost {
         self.digest = answer;
         self
@@ -496,6 +508,15 @@ impl HostFunctions for FakeHost {
         }
     }
 
+    fn check_signature(&self, message: &[u8], signature: &[u8], pubkey: &[u8]) -> HostResult<i32> {
+        self.sigs_checked.borrow_mut().push((
+            message.to_vec(),
+            signature.to_vec(),
+            pubkey.to_vec(),
+        ));
+        self.sig_valid
+    }
+
     fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
         self.digested.borrow_mut().push(data.to_vec());
         self.digest.fill(out)
@@ -554,6 +575,7 @@ pub mod import {
     pub const TX_INNER_ARR_LEN: &str = r#"(import "host_lib" "tx_inner_arr_len" (func $tx_inner_arr_len (param i32 i32) (result i32)))"#;
     pub const HOME_LE_INNER_ARR_LEN: &str = r#"(import "host_lib" "home_le_inner_arr_len" (func $home_le_inner_arr_len (param i32 i32) (result i32)))"#;
     pub const LE_INNER_ARR_LEN: &str = r#"(import "host_lib" "le_inner_arr_len" (func $le_inner_arr_len (param i32 i32 i32) (result i32)))"#;
+    pub const CHECK_SIG: &str = r#"(import "host_lib" "check_sig" (func $check_sig (param i32 i32 i32 i32 i32 i32) (result i32)))"#;
     pub const SHA512_HALF: &str = r#"(import "host_lib" "sha512_half" (func $sha512_half (param i32 i32 i32 i32) (result i32)))"#;
     pub const TRACE: &str =
         r#"(import "host_lib" "trace" (func $trace (param i32 i32 i32 i32 i32) (result i32)))"#;

include/xrpl/tx/wasm/HostContext.h

@@ -113,6 +113,13 @@ public:
     getLedgerObjNestedArrayLen(std::int32_t cacheIdx, rust::Slice<std::uint8_t const> locator)
         const noexcept;
 
+    // Answers 1/0 for a valid/invalid signature, or a negative `HostFunctionError`.
+    [[nodiscard]] std::int32_t
+    checkSignature(
+        rust::Slice<std::uint8_t const> message,
+        rust::Slice<std::uint8_t const> signature,
+        rust::Slice<std::uint8_t const> pubkey) const noexcept;
+
     [[nodiscard]] std::int32_t
     sha512Half(rust::Slice<std::uint8_t const> data, rust::Slice<std::uint8_t> out) const noexcept;
 

src/libxrpl/tx/wasm/HostContext.cpp

@@ -393,6 +393,24 @@ HostContext::getLedgerObjNestedArrayLen(
     });
 }
 
+std::int32_t
+HostContext::checkSignature(
+    rust::Slice<std::uint8_t const> message,
+    rust::Slice<std::uint8_t const> signature,
+    rust::Slice<std::uint8_t const> pubkey) const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        auto const valid = hostFunctions_.checkSignature(
+            Slice{message.data(), message.size()},
+            Slice{signature.data(), signature.size()},
+            Slice{pubkey.data(), pubkey.size()});
+        if (!valid)
+            return hfErrorToInt(valid.error());
+
+        return *valid;
+    });
+}
+
 std::int32_t
 HostContext::sha512Half(rust::Slice<std::uint8_t const> data, rust::Slice<std::uint8_t> out)
     const noexcept