CPI size restrictions are too strict

[jstarry]

Problem

Currently, the restriction on the serialized size of cpi instructions is too strict. The current CPI size restriction is useful for preventing programs from invoking overly large instructions that wouldn't otherwise be possible to invoked via serialized transaction instructions. However, with the introduction of address lookup tables, it will soon be possible to invoke transaction instructions with many more accounts and so this restriction needs to be adjusted to allow programs to have the same ability to invoke instructions with more accounts.

There are two different checks imposed on CPI's:

1. check_instruction_size which enforces that 34 * ix.accounts.len() + ix.data.len() <= 1280
   

   solana/programs/bpf_loader/src/syscalls.rs

   Lines 2750 to 2763 in 15d18a0

   	fn check_instruction_size(
   	num_accounts: usize,
   	data_len: usize,
   	invoke_context: &mut InvokeContext,
   	) -> Result<(), EbpfError<BpfError>> {
   	let size = num_accounts
   	.saturating_mul(size_of::<AccountMeta>())
   	.saturating_add(data_len);
   	let max_size = invoke_context.get_compute_budget().max_cpi_instruction_size;
   	if size > max_size {
   	return Err(SyscallError::InstructionTooLarge(size, max_size).into());
   	}
   	Ok(())
   	}

2. check_account_infos which enforces that 32 * account_infos.len() <= 1280
   

   solana/programs/bpf_loader/src/syscalls.rs

   Lines 2765 to 2785 in 15d18a0

   	fn check_account_infos(
   	len: usize,
   	invoke_context: &mut InvokeContext,
   	) -> Result<(), EbpfError<BpfError>> {
   	let adjusted_len = if invoke_context
   	.feature_set
   	.is_active(&syscall_saturated_math::id())
   	{
   	len.saturating_mul(size_of::<Pubkey>())
   	} else {
   	#[allow(clippy::integer_arithmetic)]
   	{
   	len * size_of::<Pubkey>()
   	}
   	};
   	if adjusted_len > invoke_context.get_compute_budget().max_cpi_instruction_size {
   	// Cap the number of account_infos a caller can pass to approximate
   	// maximum that accounts that could be passed in an instruction
   	return Err(SyscallError::TooManyAccounts.into());
   	};
   	Ok(())

Proposed Solution

• Restrict the number of instruction accounts in CPI instruction to 255 (matches max bpf program ix accounts)
• Restrict the number of account info's in CPI instruction to 64 (matches max tx account locks)
• Restrict the size of instruction data to 1280 (continue using max_cpi_instruction_size)