| Message ID | 20220525222604.2810054-5-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Emulator _regs fixes and cleanups | expand |
On Wed, May 25, 2022 at 10:26:04PM +0000, Sean Christopherson wrote: > Use a u16 instead of a u32 to track the dirty/valid status of GPRs in the > emulator. Unlike struct kvm_vcpu_arch, x86_emulate_ctxt tracks only the > "true" GPRs, i.e. doesn't include RIP in its array, and so only needs to > track 16 registers. > > Note, having 16 GPRs is a fundamental property of x86-64 and will not > change barring a massive architecture update. Legacy x86 ModRM and SIB > encodings use 3 bits for GPRs, i.e. support 8 registers. x86-64 uses a > single bit in the REX prefix for each possible reference type to double > the number of supported GPRs to 16 registers (4 bits). > > Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index dd1bf116a9ed..afb115b6a5a4 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -262,6 +262,9 @@ static ulong *reg_write(struct x86_emulate_ctxt *ctxt, unsigned nr) if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS)) nr &= NR_EMULATOR_GPRS - 1; + BUILD_BUG_ON(sizeof(ctxt->regs_dirty) * BITS_PER_BYTE < NR_EMULATOR_GPRS); + BUILD_BUG_ON(sizeof(ctxt->regs_valid) * BITS_PER_BYTE < NR_EMULATOR_GPRS); + ctxt->regs_valid |= 1 << nr; ctxt->regs_dirty |= 1 << nr; return &ctxt->_regs[nr]; diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h index bdd4e9865ca9..fbe87ba78163 100644 --- a/arch/x86/kvm/kvm_emulate.h +++ b/arch/x86/kvm/kvm_emulate.h @@ -353,9 +353,9 @@ struct x86_emulate_ctxt { u8 lock_prefix; u8 rep_prefix; /* bitmaps of registers in _regs[] that can be read */ - u32 regs_valid; + u16 regs_valid; /* bitmaps of registers in _regs[] that have been written */ - u32 regs_dirty; + u16 regs_dirty; /* modrm */ u8 modrm; u8 modrm_mod;
Use a u16 instead of a u32 to track the dirty/valid status of GPRs in the emulator. Unlike struct kvm_vcpu_arch, x86_emulate_ctxt tracks only the "true" GPRs, i.e. doesn't include RIP in its array, and so only needs to track 16 registers. Note, having 16 GPRs is a fundamental property of x86-64 and will not change barring a massive architecture update. Legacy x86 ModRM and SIB encodings use 3 bits for GPRs, i.e. support 8 registers. x86-64 uses a single bit in the REX prefix for each possible reference type to double the number of supported GPRs to 16 registers (4 bits). Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/emulate.c | 3 +++ arch/x86/kvm/kvm_emulate.h | 4 ++-- 2 files changed, 5 insertions(+), 2 deletions(-)