From d2f7d49826ae62b8b5c9829292e84861d2bda2b6 Mon Sep 17 00:00:00 2001 From: Hou Wenlong Date: Tue, 2 Nov 2021 17:15:31 +0800 Subject: [PATCH] KVM: x86: Use different callback if msr access comes from the emulator If msr access triggers an exit to userspace, the complete_userspace_io callback would skip instruction by vendor callback for kvm_skip_emulated_instruction(). However, when msr access comes from the emulator, e.g. if kvm.force_emulation_prefix is enabled and the guest uses rdmsr/wrmsr with kvm prefix, VM_EXIT_INSTRUCTION_LEN in vmcs is invalid and kvm_emulate_instruction() should be used to skip instruction instead. As Sean noted, unlike the previous case, there's no #UD if unrestricted guest is disabled and the guest accesses an MSR in Big RM. So the correct way to fix this is to attach a different callback when the msr access comes from the emulator. Suggested-by: Sean Christopherson Signed-off-by: Hou Wenlong Signed-off-by: Paolo Bonzini Message-Id: <34208da8f51580a06e45afefac95afea0e3f96e3.1635842679.git.houwenlong93@linux.alibaba.com> --- arch/x86/kvm/x86.c | 87 ++++++++++++++++++++++++++-------------------- 1 file changed, 50 insertions(+), 37 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 4464aa7931cd..16f7d20ed19c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -118,6 +118,7 @@ static void enter_smm(struct kvm_vcpu *vcpu); static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags); static void store_regs(struct kvm_vcpu *vcpu); static int sync_regs(struct kvm_vcpu *vcpu); +static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu); static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2); static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2); @@ -710,6 +711,17 @@ int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err) } EXPORT_SYMBOL_GPL(kvm_complete_insn_gp); +static int complete_emulated_insn_gp(struct kvm_vcpu *vcpu, int err) +{ + if (err) { + kvm_inject_gp(vcpu, 0); + return 1; + } + + return kvm_emulate_instruction(vcpu, EMULTYPE_NO_DECODE | EMULTYPE_SKIP | + EMULTYPE_COMPLETE_USER_EXIT); +} + void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault) { ++vcpu->stat.pf_guest; @@ -1815,22 +1827,36 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data) } EXPORT_SYMBOL_GPL(kvm_set_msr); -static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu) +static void complete_userspace_rdmsr(struct kvm_vcpu *vcpu) { - int err = vcpu->run->msr.error; - if (!err) { + if (!vcpu->run->msr.error) { kvm_rax_write(vcpu, (u32)vcpu->run->msr.data); kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32); } - - return static_call(kvm_x86_complete_emulated_msr)(vcpu, err); } -static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu) +static int complete_emulated_msr_access(struct kvm_vcpu *vcpu) +{ + return complete_emulated_insn_gp(vcpu, vcpu->run->msr.error); +} + +static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu) +{ + complete_userspace_rdmsr(vcpu); + return complete_emulated_msr_access(vcpu); +} + +static int complete_fast_msr_access(struct kvm_vcpu *vcpu) { return static_call(kvm_x86_complete_emulated_msr)(vcpu, vcpu->run->msr.error); } +static int complete_fast_rdmsr(struct kvm_vcpu *vcpu) +{ + complete_userspace_rdmsr(vcpu); + return complete_fast_msr_access(vcpu); +} + static u64 kvm_msr_reason(int r) { switch (r) { @@ -1865,18 +1891,6 @@ static int kvm_msr_user_space(struct kvm_vcpu *vcpu, u32 index, return 1; } -static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index, int r) -{ - return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_RDMSR, 0, - complete_emulated_rdmsr, r); -} - -static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data, int r) -{ - return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_WRMSR, data, - complete_emulated_wrmsr, r); -} - int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu) { u32 ecx = kvm_rcx_read(vcpu); @@ -1885,18 +1899,16 @@ int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu) r = kvm_get_msr(vcpu, ecx, &data); - /* MSR read failed? See if we should ask user space */ - if (r && kvm_get_msr_user_space(vcpu, ecx, r)) { - /* Bounce to user space */ - return 0; - } - if (!r) { trace_kvm_msr_read(ecx, data); kvm_rax_write(vcpu, data & -1u); kvm_rdx_write(vcpu, (data >> 32) & -1u); } else { + /* MSR read failed? See if we should ask user space */ + if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_RDMSR, 0, + complete_fast_rdmsr, r)) + return 0; trace_kvm_msr_read_ex(ecx); } @@ -1912,19 +1924,18 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu) r = kvm_set_msr(vcpu, ecx, data); - /* MSR write failed? See if we should ask user space */ - if (r && kvm_set_msr_user_space(vcpu, ecx, data, r)) - /* Bounce to user space */ - return 0; - - /* Signal all other negative errors to userspace */ - if (r < 0) - return r; - - if (!r) + if (!r) { trace_kvm_msr_write(ecx, data); - else + } else { + /* MSR write failed? See if we should ask user space */ + if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_WRMSR, data, + complete_fast_msr_access, r)) + return 0; + /* Signal all other negative errors to userspace */ + if (r < 0) + return r; trace_kvm_msr_write_ex(ecx, data); + } return static_call(kvm_x86_complete_emulated_msr)(vcpu, r); } @@ -7400,7 +7411,8 @@ static int emulator_get_msr(struct x86_emulate_ctxt *ctxt, r = kvm_get_msr(vcpu, msr_index, pdata); - if (r && kvm_get_msr_user_space(vcpu, msr_index, r)) { + if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, + complete_emulated_rdmsr, r)) { /* Bounce to user space */ return X86EMUL_IO_NEEDED; } @@ -7416,7 +7428,8 @@ static int emulator_set_msr(struct x86_emulate_ctxt *ctxt, r = kvm_set_msr(vcpu, msr_index, data); - if (r && kvm_set_msr_user_space(vcpu, msr_index, data, r)) { + if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data, + complete_emulated_msr_access, r)) { /* Bounce to user space */ return X86EMUL_IO_NEEDED; }