Adds read/write/get_pod() fns to tiered storage (solana-labs#34415)

accounts-db/src/tiered_storage/byte_block.rs

@@ -53,11 +53,31 @@ impl ByteBlockWriter {
         self.len
     }
 
+    /// Write plain ol' data to the internal buffer of the ByteBlockWriter instance
+    ///
+    /// Prefer this over `write_type()`, as it prevents some undefined behavior.
+    pub fn write_pod<T: bytemuck::NoUninit>(&mut self, value: &T) -> IoResult<usize> {
+        // SAFETY: Since T is NoUninit, it does not contain any uninitialized bytes.
+        unsafe { self.write_type(value) }
+    }
+
     /// Write the specified typed instance to the internal buffer of
     /// the ByteBlockWriter instance.
-    pub fn write_type<T>(&mut self, value: &T) -> IoResult<usize> {
+    ///
+    /// Prefer `write_pod()` when possible, because `write_type()` may cause
+    /// undefined behavior if `value` contains uninitialized bytes.
+    ///
+    /// # Safety
+    ///
+    /// Caller must ensure casting T to bytes is safe.
+    /// Refer to the Safety sections in std::slice::from_raw_parts()
+    /// and bytemuck's Pod and NoUninit for more information.
+    pub unsafe fn write_type<T>(&mut self, value: &T) -> IoResult<usize> {
         let size = mem::size_of::<T>();
         let ptr = value as *const _ as *const u8;
+        // SAFETY: The caller ensures that `value` contains no uninitialized bytes,
+        // we ensure the size is safe by querying T directly,
+        // and Rust ensures all values are at least byte-aligned.
         let slice = unsafe { std::slice::from_raw_parts(ptr, size) };
         self.write(slice)?;
         Ok(size)
@@ -73,10 +93,10 @@ impl ByteBlockWriter {
     ) -> IoResult<usize> {
         let mut size = 0;
         if let Some(rent_epoch) = opt_fields.rent_epoch {
-            size += self.write_type(&rent_epoch)?;
+            size += self.write_pod(&rent_epoch)?;
         }
         if let Some(hash) = opt_fields.account_hash {
-            size += self.write_type(&hash)?;
+            size += self.write_pod(&hash)?;
         }
 
         debug_assert_eq!(size, opt_fields.size());
@@ -112,18 +132,40 @@ impl ByteBlockWriter {
 /// The util struct for reading byte blocks.
 pub struct ByteBlockReader;
 
+/// Reads the raw part of the input byte_block, at the specified offset, as type T.
+///
+/// Returns None if `offset` + size_of::<T>() exceeds the size of the input byte_block.
+///
+/// Type T must be plain ol' data to ensure no undefined behavior.
+pub fn read_pod<T: bytemuck::AnyBitPattern>(byte_block: &[u8], offset: usize) -> Option<&T> {
+    // SAFETY: Since T is AnyBitPattern, it is safe to cast bytes to T.
+    unsafe { read_type(byte_block, offset) }
+}
+
 /// Reads the raw part of the input byte_block at the specified offset
 /// as type T.
 ///
 /// If `offset` + size_of::<T>() exceeds the size of the input byte_block,
 /// then None will be returned.
-pub fn read_type<T>(byte_block: &[u8], offset: usize) -> Option<&T> {
+///
+/// Prefer `read_pod()` when possible, because `read_type()` may cause
+/// undefined behavior.
+///
+/// # Safety
+///
+/// Caller must ensure casting bytes to T is safe.
+/// Refer to the Safety sections in std::slice::from_raw_parts()
+/// and bytemuck's Pod and AnyBitPattern for more information.
+pub unsafe fn read_type<T>(byte_block: &[u8], offset: usize) -> Option<&T> {
     let (next, overflow) = offset.overflowing_add(std::mem::size_of::<T>());
     if overflow || next > byte_block.len() {
         return None;
     }
     let ptr = byte_block[offset..].as_ptr() as *const T;
     debug_assert!(ptr as usize % std::mem::align_of::<T>() == 0);
+    // SAFETY: The caller ensures it is safe to cast bytes to T,
+    // we ensure the size is safe by querying T directly,
+    // and we just checked above to ensure the ptr is aligned for T.
     Some(unsafe { &*ptr })
 }
 
@@ -169,7 +211,7 @@ mod tests {
         let mut writer = ByteBlockWriter::new(format);
         let value: u32 = 42;
 
-        writer.write_type(&value).unwrap();
+        writer.write_pod(&value).unwrap();
         assert_eq!(writer.raw_len(), mem::size_of::<u32>());
 
         let buffer = writer.finish().unwrap();
@@ -231,12 +273,14 @@ mod tests {
         let test_data3 = [33u8; 300];
 
         // Write the above meta and data in an interleaving way.
-        writer.write_type(&test_metas[0]).unwrap();
-        writer.write_type(&test_data1).unwrap();
-        writer.write_type(&test_metas[1]).unwrap();
-        writer.write_type(&test_data2).unwrap();
-        writer.write_type(&test_metas[2]).unwrap();
-        writer.write_type(&test_data3).unwrap();
+        unsafe {
+            writer.write_type(&test_metas[0]).unwrap();
+            writer.write_type(&test_data1).unwrap();
+            writer.write_type(&test_metas[1]).unwrap();
+            writer.write_type(&test_data2).unwrap();
+            writer.write_type(&test_metas[2]).unwrap();
+            writer.write_type(&test_data3).unwrap();
+        }
         assert_eq!(
             writer.raw_len(),
             mem::size_of::<TestMetaStruct>() * 3
@@ -346,13 +390,13 @@ mod tests {
         let mut offset = 0;
         for opt_fields in &opt_fields_vec {
             if let Some(expected_rent_epoch) = opt_fields.rent_epoch {
-                let rent_epoch = read_type::<Epoch>(&decoded_buffer, offset).unwrap();
+                let rent_epoch = read_pod::<Epoch>(&decoded_buffer, offset).unwrap();
                 assert_eq!(*rent_epoch, expected_rent_epoch);
                 verified_count += 1;
                 offset += std::mem::size_of::<Epoch>();
             }
             if let Some(expected_hash) = opt_fields.account_hash {
-                let hash = read_type::<AccountHash>(&decoded_buffer, offset).unwrap();
+                let hash = read_pod::<AccountHash>(&decoded_buffer, offset).unwrap();
                 assert_eq!(hash, &expected_hash);
                 verified_count += 1;
                 offset += std::mem::size_of::<AccountHash>();

accounts-db/src/tiered_storage/file.rs

@@ -1,8 +1,11 @@
-use std::{
-    fs::{File, OpenOptions},
-    io::{Read, Result as IoResult, Seek, SeekFrom, Write},
-    mem,
-    path::Path,
+use {
+    bytemuck::{AnyBitPattern, NoUninit},
+    std::{
+        fs::{File, OpenOptions},
+        io::{Read, Result as IoResult, Seek, SeekFrom, Write},
+        mem,
+        path::Path,
+    },
 };
 
 #[derive(Debug)]
@@ -33,14 +36,53 @@ impl TieredStorageFile {
         ))
     }
 
-    pub fn write_type<T>(&self, value: &T) -> IoResult<usize> {
+    /// Writes `value` to the file.
+    ///
+    /// `value` must be plain ol' data.
+    pub fn write_pod<T: NoUninit>(&self, value: &T) -> IoResult<usize> {
+        // SAFETY: Since T is NoUninit, it does not contain any uninitialized bytes.
+        unsafe { self.write_type(value) }
+    }
+
+    /// Writes `value` to the file.
+    ///
+    /// Prefer `write_pod` when possible, because `write_value` may cause
+    /// undefined behavior if `value` contains uninitialized bytes.
+    ///
+    /// # Safety
+    ///
+    /// Caller must ensure casting T to bytes is safe.
+    /// Refer to the Safety sections in std::slice::from_raw_parts()
+    /// and bytemuck's Pod and NoUninit for more information.
+    pub unsafe fn write_type<T>(&self, value: &T) -> IoResult<usize> {
         let ptr = value as *const _ as *const u8;
         let bytes = unsafe { std::slice::from_raw_parts(ptr, mem::size_of::<T>()) };
         self.write_bytes(bytes)
     }
 
-    pub fn read_type<T>(&self, value: &mut T) -> IoResult<()> {
+    /// Reads a value of type `T` from the file.
+    ///
+    /// Type T must be plain ol' data.
+    pub fn read_pod<T: NoUninit + AnyBitPattern>(&self, value: &mut T) -> IoResult<()> {
+        // SAFETY: Since T is AnyBitPattern, it is safe to cast bytes to T.
+        unsafe { self.read_type(value) }
+    }
+
+    /// Reads a value of type `T` from the file.
+    ///
+    /// Prefer `read_pod()` when possible, because `read_type()` may cause
+    /// undefined behavior.
+    ///
+    /// # Safety
+    ///
+    /// Caller must ensure casting bytes to T is safe.
+    /// Refer to the Safety sections in std::slice::from_raw_parts()
+    /// and bytemuck's Pod and AnyBitPattern for more information.
+    pub unsafe fn read_type<T>(&self, value: &mut T) -> IoResult<()> {
         let ptr = value as *mut _ as *mut u8;
+        // SAFETY: The caller ensures it is safe to cast bytes to T,
+        // we ensure the size is safe by querying T directly,
+        // and Rust ensures ptr is aligned.
         let bytes = unsafe { std::slice::from_raw_parts_mut(ptr, mem::size_of::<T>()) };
         self.read_bytes(bytes)
     }

accounts-db/src/tiered_storage/footer.rs

@@ -1,7 +1,10 @@
 use {
     crate::tiered_storage::{
-        error::TieredStorageError, file::TieredStorageFile, index::IndexBlockFormat,
-        mmap_utils::get_type, TieredStorageResult,
+        error::TieredStorageError,
+        file::TieredStorageFile,
+        index::IndexBlockFormat,
+        mmap_utils::{get_pod, get_type},
+        TieredStorageResult,
     },
     bytemuck::{Pod, Zeroable},
     memmap2::Mmap,
@@ -204,8 +207,9 @@ impl TieredStorageFooter {
     }
 
     pub fn write_footer_block(&self, file: &TieredStorageFile) -> TieredStorageResult<()> {
-        file.write_type(self)?;
-        file.write_type(&TieredStorageMagicNumber::default())?;
+        // SAFETY: The footer does not contain any uninitialized bytes.
+        unsafe { file.write_type(self)? };
+        file.write_pod(&TieredStorageMagicNumber::default())?;
 
         Ok(())
     }
@@ -214,13 +218,13 @@ impl TieredStorageFooter {
         file.seek_from_end(-(FOOTER_TAIL_SIZE as i64))?;
 
         let mut footer_version: u64 = 0;
-        file.read_type(&mut footer_version)?;
+        file.read_pod(&mut footer_version)?;
         if footer_version != FOOTER_FORMAT_VERSION {
             return Err(TieredStorageError::InvalidFooterVersion(footer_version));
         }
 
         let mut footer_size: u64 = 0;
-        file.read_type(&mut footer_size)?;
+        file.read_pod(&mut footer_size)?;
         if footer_size != FOOTER_SIZE as u64 {
             return Err(TieredStorageError::InvalidFooterSize(
                 footer_size,
@@ -229,7 +233,7 @@ impl TieredStorageFooter {
         }
 
         let mut magic_number = TieredStorageMagicNumber::zeroed();
-        file.read_type(&mut magic_number)?;
+        file.read_pod(&mut magic_number)?;
         if magic_number != TieredStorageMagicNumber::default() {
             return Err(TieredStorageError::MagicNumberMismatch(
                 TieredStorageMagicNumber::default().0,
@@ -239,7 +243,9 @@ impl TieredStorageFooter {
 
         let mut footer = Self::default();
         file.seek_from_end(-(footer_size as i64))?;
-        file.read_type(&mut footer)?;
+        // SAFETY: We sanitize the footer to ensure all the bytes are
+        // actually safe to interpret as a TieredStorageFooter.
+        unsafe { file.read_type(&mut footer)? };
         Self::sanitize(&footer)?;
 
         Ok(footer)
@@ -248,20 +254,20 @@ impl TieredStorageFooter {
     pub fn new_from_mmap(mmap: &Mmap) -> TieredStorageResult<&TieredStorageFooter> {
         let offset = mmap.len().saturating_sub(FOOTER_TAIL_SIZE);
 
-        let (footer_version, offset) = get_type::<u64>(mmap, offset)?;
+        let (footer_version, offset) = get_pod::<u64>(mmap, offset)?;
         if *footer_version != FOOTER_FORMAT_VERSION {
             return Err(TieredStorageError::InvalidFooterVersion(*footer_version));
         }
 
-        let (&footer_size, offset) = get_type::<u64>(mmap, offset)?;
+        let (&footer_size, offset) = get_pod::<u64>(mmap, offset)?;
         if footer_size != FOOTER_SIZE as u64 {
             return Err(TieredStorageError::InvalidFooterSize(
                 footer_size,
                 FOOTER_SIZE as u64,
             ));
         }
 
-        let (magic_number, _offset) = get_type::<TieredStorageMagicNumber>(mmap, offset)?;
+        let (magic_number, _offset) = get_pod::<TieredStorageMagicNumber>(mmap, offset)?;
         if *magic_number != TieredStorageMagicNumber::default() {
             return Err(TieredStorageError::MagicNumberMismatch(
                 TieredStorageMagicNumber::default().0,
@@ -270,7 +276,9 @@ impl TieredStorageFooter {
         }
 
         let footer_offset = mmap.len().saturating_sub(footer_size as usize);
-        let (footer, _offset) = get_type::<TieredStorageFooter>(mmap, footer_offset)?;
+        // SAFETY: We sanitize the footer to ensure all the bytes are
+        // actually safe to interpret as a TieredStorageFooter.
+        let (footer, _offset) = unsafe { get_type::<TieredStorageFooter>(mmap, footer_offset)? };
         Self::sanitize(footer)?;
 
         Ok(footer)

accounts-db/src/tiered_storage/hot.rs

@@ -10,7 +10,7 @@ use {
             },
             index::{AccountOffset, IndexBlockFormat, IndexOffset},
             meta::{AccountMetaFlags, AccountMetaOptionalFields, TieredAccountMeta},
-            mmap_utils::get_type,
+            mmap_utils::get_pod,
             owners::{OwnerOffset, OwnersBlock},
             TieredStorageError, TieredStorageFormat, TieredStorageResult,
         },
@@ -204,7 +204,7 @@ impl TieredAccountMeta for HotAccountMeta {
             .then(|| {
                 let offset = self.optional_fields_offset(account_block)
                     + AccountMetaOptionalFields::rent_epoch_offset(self.flags());
-                byte_block::read_type::<Epoch>(account_block, offset).copied()
+                byte_block::read_pod::<Epoch>(account_block, offset).copied()
             })
             .flatten()
     }
@@ -217,7 +217,7 @@ impl TieredAccountMeta for HotAccountMeta {
             .then(|| {
                 let offset = self.optional_fields_offset(account_block)
                     + AccountMetaOptionalFields::account_hash_offset(self.flags());
-                byte_block::read_type::<AccountHash>(account_block, offset)
+                byte_block::read_pod::<AccountHash>(account_block, offset)
             })
             .flatten()
     }
@@ -283,7 +283,7 @@ impl HotStorageReader {
     ) -> TieredStorageResult<&HotAccountMeta> {
         let internal_account_offset = account_offset.offset();
 
-        let (meta, _) = get_type::<HotAccountMeta>(&self.mmap, internal_account_offset)?;
+        let (meta, _) = get_pod::<HotAccountMeta>(&self.mmap, internal_account_offset)?;
         Ok(meta)
     }
 
@@ -452,13 +452,16 @@ pub mod tests {
             .with_flags(&flags);
 
         let mut writer = ByteBlockWriter::new(AccountBlockFormat::AlignedRaw);
-        writer.write_type(&expected_meta).unwrap();
-        writer.write_type(&account_data).unwrap();
-        writer.write_type(&padding).unwrap();
+        writer.write_pod(&expected_meta).unwrap();
+        // SAFETY: These values are POD, so they are safe to write.
+        unsafe {
+            writer.write_type(&account_data).unwrap();
+            writer.write_type(&padding).unwrap();
+        }
         writer.write_optional_fields(&optional_fields).unwrap();
         let buffer = writer.finish().unwrap();
 
-        let meta = byte_block::read_type::<HotAccountMeta>(&buffer, 0).unwrap();
+        let meta = byte_block::read_pod::<HotAccountMeta>(&buffer, 0).unwrap();
         assert_eq!(expected_meta, *meta);
         assert!(meta.flags().has_rent_epoch());
         assert!(meta.flags().has_account_hash());
@@ -548,7 +551,7 @@ pub mod tests {
                 .iter()
                 .map(|meta| {
                     let prev_offset = current_offset;
-                    current_offset += file.write_type(meta).unwrap();
+                    current_offset += file.write_pod(meta).unwrap();
                     HotAccountOffset::new(prev_offset).unwrap()
                 })
                 .collect();