From 8c989da68342918f1717c60aa60fdfab7d1e676e Mon Sep 17 00:00:00 2001
From: Jack May <jack@solana.com>
Date: Fri, 2 Oct 2020 00:33:37 -0700
Subject: [PATCH] Fix zero-len slice translations

---
 programs/bpf/rust/invoke/src/lib.rs  | 10 ++++++++
 programs/bpf/rust/invoked/src/lib.rs |  4 ++++
 programs/bpf_loader/src/syscalls.rs  | 36 +++++++++++++++++++++-------
 3 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/programs/bpf/rust/invoke/src/lib.rs b/programs/bpf/rust/invoke/src/lib.rs
index feee567c8c..b29212eeb4 100644
--- a/programs/bpf/rust/invoke/src/lib.rs
+++ b/programs/bpf/rust/invoke/src/lib.rs
@@ -83,6 +83,16 @@ fn process_instruction(
                 invoke(&instruction, accounts)?;
             }
 
+            info!("Test no instruction data");
+            {
+                let instruction = create_instruction(
+                    *accounts[INVOKED_PROGRAM_INDEX].key,
+                    &[(accounts[ARGUMENT_INDEX].key, true, true)],
+                    vec![],
+                );
+                invoke(&instruction, accounts)?;
+            }
+
             info!("Test return error");
             {
                 let instruction = create_instruction(
diff --git a/programs/bpf/rust/invoked/src/lib.rs b/programs/bpf/rust/invoked/src/lib.rs
index b976697a88..6226d9ea98 100644
--- a/programs/bpf/rust/invoked/src/lib.rs
+++ b/programs/bpf/rust/invoked/src/lib.rs
@@ -26,6 +26,10 @@ fn process_instruction(
 ) -> ProgramResult {
     info!("Invoked program");
 
+    if instruction_data.is_empty() {
+        return Ok(());
+    }
+
     match instruction_data[0] {
         TEST_VERIFY_TRANSLATIONS => {
             info!("verify data translations");
diff --git a/programs/bpf_loader/src/syscalls.rs b/programs/bpf_loader/src/syscalls.rs
index 38f78e9ae2..4810b58340 100644
--- a/programs/bpf_loader/src/syscalls.rs
+++ b/programs/bpf_loader/src/syscalls.rs
@@ -169,15 +169,19 @@ macro_rules! translate_type {
 #[macro_export]
 macro_rules! translate_slice_mut {
     ($t:ty, $vm_addr:expr, $len: expr, $regions:expr) => {
-        match translate_addr::<BPFError>(
-            $vm_addr as u64,
-            $len as usize * size_of::<$t>(),
-            file!(),
-            line!() as usize - ELF_INSN_DUMP_OFFSET + 1,
-            $regions,
-        ) {
-            Ok(value) => Ok(unsafe { from_raw_parts_mut(value as *mut $t, $len as usize) }),
-            Err(e) => Err(e),
+        if $len == 0 {
+            Ok(unsafe { from_raw_parts_mut(0x1 as *mut $t, $len as usize) })
+        } else {
+            match translate_addr::<BPFError>(
+                $vm_addr as u64,
+                $len as usize * size_of::<$t>(),
+                file!(),
+                line!() as usize - ELF_INSN_DUMP_OFFSET + 1,
+                $regions,
+            ) {
+                Ok(value) => Ok(unsafe { from_raw_parts_mut(value as *mut $t, $len as usize) }),
+                Err(e) => Err(e),
+            }
         }
     };
 }
@@ -935,6 +939,20 @@ mod tests {
 
     #[test]
     fn test_translate_slice() {
+        // zero len
+        let good_data = vec![1u8, 2, 3, 4, 5];
+        let data: Vec<u8> = vec![];
+        assert_eq!(0x1 as *const u8, data.as_ptr());
+        let addr = good_data.as_ptr() as *const _ as u64;
+        let regions = vec![MemoryRegion {
+            addr_host: addr,
+            addr_vm: 100,
+            len: good_data.len() as u64,
+        }];
+        let translated_data = translate_slice!(u8, data.as_ptr(), data.len(), &regions).unwrap();
+        assert_eq!(data, translated_data);
+        assert_eq!(0, translated_data.len());
+
         // u8
         let mut data = vec![1u8, 2, 3, 4, 5];
         let addr = data.as_ptr() as *const _ as u64;