From c4db4f3706c0da9dec41ade58d552151d3e335f1 Mon Sep 17 00:00:00 2001 From: Alessandro Decina Date: Fri, 17 Nov 2023 21:02:25 +1100 Subject: [PATCH] cpi: direct_mapping: always zero spare capacity if account alloc changes If the vector holding an account is reallocated during execution of a callee, we must zero the spare capacity regardless of whether the account size changed, because the underlying vector might contain uninitialized memory in the spare capacity. --- programs/bpf_loader/src/syscalls/cpi.rs | 179 ++++++++++++---------- programs/sbf/rust/invoke/src/processor.rs | 28 ++++ 2 files changed, 126 insertions(+), 81 deletions(-) diff --git a/programs/bpf_loader/src/syscalls/cpi.rs b/programs/bpf_loader/src/syscalls/cpi.rs index 715662c4a06dbe..13f9cbaf905275 100644 --- a/programs/bpf_loader/src/syscalls/cpi.rs +++ b/programs/bpf_loader/src/syscalls/cpi.rs @@ -1302,11 +1302,14 @@ fn update_caller_account( caller_account.vm_data_addr, caller_account.original_data_len, )? { - // Since each instruction account is directly mapped in a memory region - // with a *fixed* length, upon returning from CPI we must ensure that the - // current capacity is at least the original length (what is mapped in - // memory), so that the account's memory region never points to an - // invalid address. + // Since each instruction account is directly mapped in a memory region with a *fixed* + // length, upon returning from CPI we must ensure that the current capacity is at least + // the original length (what is mapped in memory), so that the account's memory region + // never points to an invalid address. + // + // Note that the capacity can be smaller than the original length only if the account is + // reallocated using the AccountSharedData API directly (deprecated). BorrowedAccount + // and CoW don't trigger this, see BorrowedAccount::make_data_mut. let min_capacity = caller_account.original_data_len; if callee_account.capacity() < min_capacity { callee_account @@ -1314,10 +1317,13 @@ fn update_caller_account( zero_all_mapped_spare_capacity = true; } - // If an account's data pointer has changed - because of CoW, reserve() as called above - // or because of using AccountSharedData directly (deprecated) - we must update the - // corresponding MemoryRegion in the caller's address space. Address spaces are fixed so - // we don't need to update the MemoryRegion's length. + // If an account's data pointer has changed we must update the corresponding + // MemoryRegion in the caller's address space. Address spaces are fixed so we don't need + // to update the MemoryRegion's length. + // + // An account's data pointer can change if the account is reallocated because of CoW, + // because of BorrowedAccount::make_data_mut or by a program that uses the + // AccountSharedData API directly (deprecated). let callee_ptr = callee_account.get_data().as_ptr() as u64; if region.host_addr.get() != callee_ptr { region.host_addr.set(callee_ptr); @@ -1328,7 +1334,6 @@ fn update_caller_account( let prev_len = *caller_account.ref_to_len_in_vm.get()? as usize; let post_len = callee_account.get_data().len(); - let realloc_bytes_used = post_len.saturating_sub(caller_account.original_data_len); if prev_len != post_len { let max_increase = if direct_mapping && !invoke_context.get_check_aligned() { 0 @@ -1352,37 +1357,8 @@ fn update_caller_account( if post_len < prev_len { if direct_mapping { // We have two separate regions to zero out: the account data - // and the realloc region. - // - // Here we zero the account data region. - let spare_len = if zero_all_mapped_spare_capacity { - // In the unlikely case where the account data vector has - // changed - which can happen during CoW - we zero the whole - // extra capacity up to the original data length. - // - // The extra capacity up to original data length is - // accessible from the vm and since it's uninitialized - // memory, it could be a source of non determinism. - caller_account.original_data_len - } else { - // If the allocation has not changed, we only zero the - // difference between the previous and current lengths. The - // rest of the memory contains whatever it contained before, - // which is deterministic. - prev_len - } - .saturating_sub(post_len); - if spare_len > 0 { - let dst = callee_account - .spare_data_capacity_mut()? - .get_mut(..spare_len) - .ok_or_else(|| Box::new(InstructionError::AccountDataTooSmall))? - .as_mut_ptr(); - // Safety: we check bounds above - unsafe { ptr::write_bytes(dst, 0, spare_len) }; - } - - // Here we zero the realloc region. + // and the realloc region. Here we zero the realloc region, the + // data region is zeroed further down below. // // This is done for compatibility but really only necessary for // the fringe case of a program calling itself, see @@ -1464,50 +1440,91 @@ fn update_caller_account( )?; *serialized_len_ptr = post_len as u64; } - if !direct_mapping { - let to_slice = &mut caller_account.serialized_data; - let from_slice = callee_account - .get_data() - .get(0..post_len) - .ok_or(SyscallError::InvalidLength)?; - if to_slice.len() != from_slice.len() { - return Err(Box::new(InstructionError::AccountDataTooSmall)); - } - to_slice.copy_from_slice(from_slice); - } else if realloc_bytes_used > 0 { - // In the is_loader_deprecated case, we must have failed with - // InvalidRealloc by now. - debug_assert!(!is_loader_deprecated); - - let to_slice = { - // If a callee reallocs an account, we write into the caller's - // realloc region regardless of whether the caller has write - // permissions to the account or not. If the callee has been able to - // make changes, it means they had permissions to do so, and here - // we're just going to reflect those changes to the caller's frame. + + if direct_mapping { + // Here we zero the account data region. + // + // If zero_all_mapped_spare_capacity=true, we need to zero regardless of whether the account + // size changed, because the underlying vector holding the account might have been + // reallocated and contain uninitialized memory in the spare capacity. + // + // See TEST_CPI_CHANGE_ACCOUNT_DATA_MEMORY_ALLOCATION for an example of + // this case. + let spare_len = if zero_all_mapped_spare_capacity { + // In the unlikely case where the account data vector has + // changed - which can happen during CoW - we zero the whole + // extra capacity up to the original data length. // - // Therefore we temporarily configure the realloc region as writable - // then set it back to whatever state it had. - let realloc_region = caller_account - .realloc_region(memory_mapping, is_loader_deprecated)? - .unwrap(); // unwrapping here is fine, we asserted !is_loader_deprecated - let original_state = realloc_region.state.replace(MemoryState::Writable); - defer! { - realloc_region.state.set(original_state); - }; + // The extra capacity up to original data length is + // accessible from the vm and since it's uninitialized + // memory, it could be a source of non determinism. + caller_account.original_data_len + } else { + // If the allocation has not changed, we only zero the + // difference between the previous and current lengths. The + // rest of the memory contains whatever it contained before, + // which is deterministic. + prev_len + } + .saturating_sub(post_len); + + if spare_len > 0 { + let dst = callee_account + .spare_data_capacity_mut()? + .get_mut(..spare_len) + .ok_or_else(|| Box::new(InstructionError::AccountDataTooSmall))? + .as_mut_ptr(); + // Safety: we check bounds above + unsafe { ptr::write_bytes(dst, 0, spare_len) }; + } - translate_slice_mut::( - memory_mapping, - caller_account - .vm_data_addr - .saturating_add(caller_account.original_data_len as u64), - realloc_bytes_used as u64, - invoke_context.get_check_aligned(), - )? - }; + // Propagate changes to the realloc region in the callee up to the caller. + let realloc_bytes_used = post_len.saturating_sub(caller_account.original_data_len); + if realloc_bytes_used > 0 { + // In the is_loader_deprecated case, we must have failed with + // InvalidRealloc by now. + debug_assert!(!is_loader_deprecated); + + let to_slice = { + // If a callee reallocs an account, we write into the caller's + // realloc region regardless of whether the caller has write + // permissions to the account or not. If the callee has been able to + // make changes, it means they had permissions to do so, and here + // we're just going to reflect those changes to the caller's frame. + // + // Therefore we temporarily configure the realloc region as writable + // then set it back to whatever state it had. + let realloc_region = caller_account + .realloc_region(memory_mapping, is_loader_deprecated)? + .unwrap(); // unwrapping here is fine, we asserted !is_loader_deprecated + let original_state = realloc_region.state.replace(MemoryState::Writable); + defer! { + realloc_region.state.set(original_state); + }; + + translate_slice_mut::( + memory_mapping, + caller_account + .vm_data_addr + .saturating_add(caller_account.original_data_len as u64), + realloc_bytes_used as u64, + invoke_context.get_check_aligned(), + )? + }; + let from_slice = callee_account + .get_data() + .get(caller_account.original_data_len..post_len) + .ok_or(SyscallError::InvalidLength)?; + if to_slice.len() != from_slice.len() { + return Err(Box::new(InstructionError::AccountDataTooSmall)); + } + to_slice.copy_from_slice(from_slice); + } + } else { + let to_slice = &mut caller_account.serialized_data; let from_slice = callee_account .get_data() - .get(caller_account.original_data_len..post_len) + .get(0..post_len) .ok_or(SyscallError::InvalidLength)?; if to_slice.len() != from_slice.len() { return Err(Box::new(InstructionError::AccountDataTooSmall)); diff --git a/programs/sbf/rust/invoke/src/processor.rs b/programs/sbf/rust/invoke/src/processor.rs index a45a6ad2dc149e..1943f8f4b578db 100644 --- a/programs/sbf/rust/invoke/src/processor.rs +++ b/programs/sbf/rust/invoke/src/processor.rs @@ -1315,6 +1315,34 @@ fn process_instruction( }, &vec![0; original_data_len - new_len] ); + + // Realloc to [0xFC; 2]. Here we keep the same length, but realloc the underlying + // vector. CPI must zero even if the length is unchanged. + invoke( + &create_instruction( + *callee_program_id, + &[ + (accounts[ARGUMENT_INDEX].key, true, false), + (callee_program_id, false, false), + ], + vec![0xFC; 2], + ), + accounts, + ) + .unwrap(); + + // Check that [2..20] is zeroed + let new_len = account.data_len(); + assert_eq!(&*account.data.borrow(), &[0xFC; 2]); + assert_eq!( + unsafe { + slice::from_raw_parts( + account.data.borrow().as_ptr().add(new_len), + original_data_len - new_len, + ) + }, + &vec![0; original_data_len - new_len] + ); } TEST_WRITE_ACCOUNT => { msg!("TEST_WRITE_ACCOUNT");