llvm-project

78ff617d - [ARM] CMSE security mitigation on function arguments and returned values (#89944)

[ARM] CMSE security mitigation on function arguments and returned values (#89944) The ABI mandates two things related to function calls: - Function arguments must be sign- or zero-extended to the register size by the caller. - Return values must be sign- or zero-extended to the register size by the callee. As consequence, callees can assume that function arguments have been extended and so can callers with regards to return values. Here lies the problem: Nonsecure code might deliberately ignore this mandate with the intent of attempting an exploit. It might try to pass values that lie outside the expected type's value range in order to trigger undefined behaviour, e.g. out of bounds access. With the mitigation implemented, Secure code always performs extension of values passed by Nonsecure code. This addresses the vulnerability described in CVE-2024-0151. Patches by Victor Campos. --------- Co-authored-by: Victor Campos <victor.campos@arm.com>