Clean up and harden the use of the x86_emulate_ctxt._regs, which is surrounded by a fair bit of magic. This series was prompted by bug reports by Kees and Robert where GCC-12 flags an out-of-bounds _regs access. The warning is a false positive due to a now-known GCC bug, but it's cheap and easy to harden the _regs usage, and doing so minimizing the risk of more precisely handling 32-bit vs. 64-bit GPRs. I didn't tag patch 2 with Fixes or Cc: stable@. It does remedy the GCC-12 warning, but AIUI the GCC-12 bug affects other KVM paths that already have explicit guardrails, i.e. fixing this one case doesn't guarantee happiness when building with CONFIG_KVM_WERROR=y, let alone CONFIG_WERROR=y. That said, it might be worth sending to the v5.18 stable tree[*] as it does appear to make some configs/setups happy. [*] KVM hasn't changed, but the warning=>error was introduced in v5.18 by commit e6148767825c ("Makefile: Enable -Warray-bounds"). v2: - Collect reviews and tests. [Vitaly, Kees, Robert] - Tweak patch 1's changelog to explicitly call out that dirty_regs is a 4 byte field. [Vitaly] - Add Reported-by for Kees and Robert since this does technically fix a build breakage. - Use a raw literal for NR_EMULATOR_GPRS instead of VCPU_REGS_R15+1 to play nice with 32-bit builds. [kernel test robot] - Reduce the number of emulated GPRs to 8 for 32-bit builds. - Add and use KVM_EMULATOR_BUG_ON() to bug/kill the VM when an emulator bug is detected. [Vitaly] v1: https://lore.kernel.org/all/20220525222604.2810054-1-seanjc@xxxxxxxxxx Sean Christopherson (8): KVM: x86: Grab regs_dirty in local 'unsigned long' KVM: x86: Harden _regs accesses to guard against buggy input KVM: x86: Omit VCPU_REGS_RIP from emulator's _regs array KVM: x86: Use 16-bit fields to track dirty/valid emulator GPRs KVM: x86: Reduce the number of emulator GPRs to '8' for 32-bit KVM KVM: x86: Bug the VM if the emulator accesses a non-existent GPR KVM: x86: Bug the VM if the emulator generates a bogus exception vector KVM: x86: Bug the VM on an out-of-bounds data read arch/x86/kvm/emulate.c | 26 ++++++++++++++++++++------ arch/x86/kvm/kvm_emulate.h | 28 +++++++++++++++++++++++++--- arch/x86/kvm/x86.c | 9 +++++++++ 3 files changed, 54 insertions(+), 9 deletions(-) base-commit: 90bde5bea810d766e7046bf5884f2ccf76dd78e9 -- 2.36.1.255.ge46751e96f-goog