Syscall Parameter Address Restrictions

Summary

Syscall parameter related changes split off from SIMD-0219: Removing pitfalls and foot-guns from the ABI (including syscalls) and runtime.

Motivation

In a recent meeting between the Agave and Firedancer core developers it was decided that SIMD-0219 should be split into two feature gates. This SIMD covers the first half which is focused on reducing the attack surface and fix long standing issues with CPI in general.

The reasoning for splitting SIMD-0219 is to de-risk its deployment and to be able to make progress on shipping earlier parts even if later parts have to be delayed further. The reason for cutting SIMD-0219 at this specific boundary is that this first half is not expected to have any impact on performance, while the second half on the other hand will.

Additionally, some consensus relevant code reordering is added to reduce the attack surface of around CU metering and make the CPI logic more comprehensible after this SIMDs feature gates are cleaned up.

New Terminology

None.

Detailed Design

Changes inherited from SIMD-0219

• The following pointers must be on the stack or heap, meaning their virtual address is inside 0x200000000..0x400000000, otherwise SyscallError::InvalidPointer must be thrown: - The destination address of all sysvar related syscalls - The pointer in the array of &[AccountInfo] / SolAccountInfo* - The AccountInfo::data field, which is a RefCell<&[u8]> in sol_invoke_signed_rust - The AccountInfo::lamports field, which is a RefCell<&u64> in sol_invoke_signed_rust
• The following pointers must point to what was originally serialized in the input regions by the program runtime, otherwise SyscallError::InvalidPointer must be thrown: - AccountInfo::key / SolAccountInfo::key - AccountInfo::owner / SolAccountInfo::owner - AccountInfo::lamports / SolAccountInfo::lamports - AccountInfo::data::ptr / SolAccountInfo::data

Additional changes

InstructionError::InvalidRealloc must be thrown on the CPI call edge if the caller requested an account length which does not fit the payload address space of the account in the caller. This check must occur after the address of the account length is translated but before the address of the account payload is translated.

InstructionError::InvalidRealloc must be thrown on the CPI return edge if the callee requested an account length which does not fit the payload address space of the account in the caller. This check currently allows for +10 KiB even in ABIv0 which is incorrect and must be reduced to 0 growth allowed in ABIv0.

All sites in the CPI code which perform guest to host address translation first and then perform pointer arithmetic on the host must be swapped such that they perform pointer arithmetic in the virtual address space first followed by the address translation second. This specifically affects the account length field.

As a consequence of the changes to the address translation of the account length field, the CU charging for the account length in CPI must be moved to occur after the address translation of the account length field.

Modifications of the callee accounts on the CPI call edge must all happen together after every account info and account meta is translated, instead of being interleaved with these.

Alternatives Considered

Leaving SIMD-0219 as is.

Impact

Splitting SIMD-0219 should have no impact on dApp developers or validators. The additional changes are continuously tested (over a month) and monitored on mainnet-beta to not cause any existing dApps to behave differently.

Security Considerations

None.