Account readwrite deescalation is not persisted in instruction execution context

[jstarry]

Problem

If a program passes a readwrite account as readonly to an inner instruction, then any writes should cause an error. Since the runtime doesn't track changes to write deescalation, it allows those instructions to succeed but will not return those state changes to the caller program due to this check:

solana/programs/bpf_loader/src/syscalls.rs

Line 1422 in 10c81a2

if message.is_writable(i) && !account.executable {

Proposed Solution

Temporarily deescalate is_writable in PreAccounts for inner instructions.

[jstarry]

Might make sense to remove both is_signer and is_writable from PreAccount actually. Then, is_writable can be passed in to the PreAccount verify functions.