Yang, Sheng wrote:
> From 9743b5299bae1779c2b893cbeb86122bcccb9b2d Mon Sep 17 00:00:00 2001
> From: Sheng Yang <[EMAIL PROTECTED]>
> Date: Wed, 2 Jan 2008 14:49:22 +0800
> Subject: [PATCH] KVM: emulator: Only allow VMCALL/VMMCALL trapped by #UD
>
> When executing a test program called "crashme", we found the KVM guest cannot
> survived more than ten seconds, then encounterd kernel panic. The basic
> concept of "crashme" is graduating random assembly code and trying to execute
> them in a fork process.
>
> After some fix on emulator valid judgment, we found it's hard to get the
> current emulator handle the invalid instructions correctly, for the #UD trap
> for hypercall patching caused troubles. The problem is, if the opcode itself
> was OK, but combination of opcode and modrm_reg was invalid, and one operand
> of the opcode was memory(SrcMem or DstMem), emulator would fetched the memory
> operand first rather than judged the validity, and may encounter error there.
>
Nice catch!
Regards,
Anthony Liguori
> For example, ".byte 0xfe, 0x34, 0xcd" got this trouble.
>
> In the patch, we simply check that if the invalid opcode isn't
> vmcall/vmmcall,
> then return from emulate_instruction() and inject a #UD to guest. With the
> patch, the guest had been run for more than 12 hours.
>
> Signed-off-by: Feng (Eric) Liu <[EMAIL PROTECTED]>
> Signed-off-by: Sheng Yang <[EMAIL PROTECTED]>
> ---
> arch/x86/kvm/svm.c | 2 +-
> arch/x86/kvm/vmx.c | 2 +-
> arch/x86/kvm/x86.c | 18 +++++++++++++++---
> include/asm-x86/kvm_host.h | 4 +++-
> 4 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 11e5baf..2da9e11 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -942,7 +942,7 @@ static int ud_interception(struct vcpu_svm *svm, struct
> kvm_run *kvm_run)
> {
> int er;
>
> - er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0, 0);
> + er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0, EMULTYPE_TRAP_UD);
> if (er != EMULATE_DONE)
> kvm_queue_exception(&svm->vcpu, UD_VECTOR);
> return 1;
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4741806..5346e42 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1862,7 +1862,7 @@ static int handle_exception(struct kvm_vcpu *vcpu,
> struct kvm_run *kvm_run)
> }
>
> if (is_invalid_opcode(intr_info)) {
> - er = emulate_instruction(vcpu, kvm_run, 0, 0, 0);
> + er = emulate_instruction(vcpu, kvm_run, 0, 0, EMULTYPE_TRAP_UD);
> if (er != EMULATE_DONE)
> kvm_queue_exception(vcpu, UD_VECTOR);
> return 1;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c5b4825..2a659ce 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1840,9 +1840,10 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
> struct kvm_run *run,
> unsigned long cr2,
> u16 error_code,
> - int no_decode)
> + int emulation_type)
> {
> int r;
> + struct decode_cache *c;
>
> vcpu->arch.mmio_fault_cr2 = cr2;
> kvm_x86_ops->cache_regs(vcpu);
> @@ -1850,7 +1851,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
> vcpu->mmio_is_write = 0;
> vcpu->arch.pio.string = 0;
>
> - if (!no_decode) {
> + if (!(emulation_type & EMULTYPE_NO_DECODE)) {
> int cs_db, cs_l;
> kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
>
> @@ -1884,6 +1885,16 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
> get_segment_base(vcpu, VCPU_SREG_FS);
>
> r = x86_decode_insn(&vcpu->arch.emulate_ctxt, &emulate_ops);
> +
> + /* Reject the instructions other than VMCALL/VMMCALL when
> + * try to emulate invalid opcode */
> + c = &vcpu->arch.emulate_ctxt.decode;
> + if ((emulation_type & EMULTYPE_TRAP_UD) &&
> + (!(c->twobyte && c->b == 0x01 &&
> + (c->modrm_reg == 0 || c->modrm_reg == 3) &&
> + c->modrm_mod == 3 && c->modrm_rm == 1)))
> + return EMULATE_FAIL;
> +
> ++vcpu->stat.insn_emulation;
> if (r) {
> ++vcpu->stat.insn_emulation_fail;
> @@ -2639,7 +2650,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu,
> struct kvm_run *kvm_run)
> vcpu->mmio_read_completed = 1;
> vcpu->mmio_needed = 0;
> r = emulate_instruction(vcpu, kvm_run,
> - vcpu->arch.mmio_fault_cr2, 0, 1);
> + vcpu->arch.mmio_fault_cr2, 0,
> + EMULTYPE_NO_DECODE);
> if (r == EMULATE_DO_MMIO) {
> /*
> * Read-modify-write. Back to userspace.
> diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
> index 20597bc..4702b04 100644
> --- a/include/asm-x86/kvm_host.h
> +++ b/include/asm-x86/kvm_host.h
> @@ -415,8 +415,10 @@ enum emulation_result {
> EMULATE_FAIL, /* can't emulate this instruction */
> };
>
> +#define EMULTYPE_NO_DECODE (1 << 0)
> +#define EMULTYPE_TRAP_UD (1 << 1)
> int emulate_instruction(struct kvm_vcpu *vcpu, struct kvm_run *run,
> - unsigned long cr2, u16 error_code, int no_decode);
> + unsigned long cr2, u16 error_code, int emulation_type);
> void kvm_report_emulation_failure(struct kvm_vcpu *cvpu, const char
> *context);
> void realmode_lgdt(struct kvm_vcpu *vcpu, u16 size, unsigned long address);
> void realmode_lidt(struct kvm_vcpu *vcpu, u16 size, unsigned long address);
>
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>
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