================ @@ -0,0 +1,133 @@ +//===--- emupac.cpp - Emulated PAC implementation -------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file implements Emulated PAC using SipHash_1_3 as the IMPDEF hashing +// scheme. +// +//===----------------------------------------------------------------------===// + +#include <stdint.h> + +#include "siphash/SipHash.h" + +// EmuPAC implements runtime emulation of PAC instructions. If the current +// CPU supports PAC, EmuPAC uses real PAC instructions. Otherwise, it uses the +// emulation, which is effectively an implementation of PAC with an IMPDEF +// hashing scheme based on SipHash_1_3. +// +// The purpose of the emulation is to allow programs to be built to be portable +// to machines without PAC support, with some performance loss and increased +// probability of false positives (due to not being able to portably determine +// the VA size), while being functionally almost equivalent to running on a +// machine with PAC support. One example of a use case is if PAC is used in +// production as a security mitigation, but the testing environment is +// heterogeneous (i.e. some machines lack PAC support). In this case we would +// like the testing machines to be able to detect issues resulting +// from the use of PAC instructions that would affect production by running +// tests. This can be achieved by building test binaries with EmuPAC and +// production binaries with real PAC. +// +// The emulation assumes that the VA size is at most 48 bits. The architecture +// as of ARMv8.2, which was the last architecture version in which PAC was not +// mandatory, permitted VA size up to 52 bits via ARMv8.2-LVA, but we are +// unaware of an ARMv8.2 CPU that implemented ARMv8.2-LVA. + +const uint64_t kMaxVASize = 48; +const uint64_t kPACMask = ((1ULL << 55) - 1) & ~((1ULL << kMaxVASize) - 1); +const uint64_t kTTBR1Mask = 1ULL << 55; ---------------- atrosinenko wrote:
[nit] According to LLVM naming convention, this probably should be simply `MaxVASize`, `PACMask`, `TTBR1Mask`. https://github.com/llvm/llvm-project/pull/133530 _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
