On Thu, Nov 22, 2012 at 03:16:47AM +0000, Xu, Dongxiao wrote:
>
>
> > -----Original Message-----
> > From: Gleb Natapov [mailto:[email protected]]
> > Sent: Wednesday, November 21, 2012 9:27 PM
> > To: Xu, Dongxiao
> > Cc: [email protected]; [email protected]
> > Subject: Re: [PATCH 1/4] nested vmx: clean up for vmcs12 read and write
> >
> > On Wed, Nov 21, 2012 at 05:04:34PM +0800, Dongxiao Xu wrote:
> > > abstract vmcs12_read and vmcs12_write functions to do the vmcs12
> > > read/write operations.
> > >
> > > Signed-off-by: Dongxiao Xu <[email protected]>
> > > ---
> > > arch/x86/kvm/vmx.c | 86
> > +++++++++++++++++++++++++++-------------------------
> > > 1 files changed, 45 insertions(+), 41 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index
> > > f858159..d8670e4 100644
> > > --- a/arch/x86/kvm/vmx.c
> > > +++ b/arch/x86/kvm/vmx.c
> > > @@ -5407,32 +5407,67 @@ static inline int vmcs_field_readonly(unsigned
> > long field)
> > > * some of the bits we return here (e.g., on 32-bit guests, only 32 bits
> > > of
> > > * 64-bit fields are to be returned).
> > > */
> > > -static inline bool vmcs12_read_any(struct kvm_vcpu *vcpu,
> > > - unsigned long field, u64 *ret)
> > > +static inline u64 vmcs12_read(struct kvm_vcpu *vcpu, unsigned long
> > > +field)
> > > {
> > > short offset = vmcs_field_to_offset(field);
> > > char *p;
> > >
> > > - if (offset < 0)
> > > + if (offset < 0) {
> > > + nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > + skip_emulated_instruction(vcpu);
> > > return 0;
> > > + }
> > >
> > > p = ((char *)(get_vmcs12(vcpu))) + offset;
> > >
> > > switch (vmcs_field_type(field)) {
> > > case VMCS_FIELD_TYPE_NATURAL_WIDTH:
> > > - *ret = *((natural_width *)p);
> > > + return *((natural_width *)p);
> > > + case VMCS_FIELD_TYPE_U16:
> > > + return *((u16 *)p);
> > > + case VMCS_FIELD_TYPE_U32:
> > > + return *((u32 *)p);
> > > + case VMCS_FIELD_TYPE_U64:
> > > + return *((u64 *)p);
> > > + default:
> > > + nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > + skip_emulated_instruction(vcpu);
> > > + return 0; /* can never happen. */
> > > + }
> > > +}
> > > +
> > > +static inline int vmcs12_write(struct kvm_vcpu *vcpu,
> > > + unsigned long field,
> > > + u64 value)
> > > +{
> > > + short offset = vmcs_field_to_offset(field);
> > > + char *p;
> > > +
> > > + if (offset < 0) {
> > > + nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > + skip_emulated_instruction(vcpu);
> > > + return 0;
> > > + }
> > > +
> > > + p = ((char *)(get_vmcs12(vcpu))) + offset;
> > > +
> > > + switch (vmcs_field_type(field)) {
> > > + case VMCS_FIELD_TYPE_NATURAL_WIDTH:
> > > + *(natural_width *)p = value;
> > > return 1;
> > > case VMCS_FIELD_TYPE_U16:
> > > - *ret = *((u16 *)p);
> > > + *(u16 *)p = value;
> > > return 1;
> > > case VMCS_FIELD_TYPE_U32:
> > > - *ret = *((u32 *)p);
> > > + *(u32 *)p = value;
> > > return 1;
> > > case VMCS_FIELD_TYPE_U64:
> > > - *ret = *((u64 *)p);
> > > + *(u64 *)p = value;
> > > return 1;
> > > default:
> > > - return 0; /* can never happen. */
> > > + nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > + skip_emulated_instruction(vcpu);
> > > + return 0;
> > > }
> > > }
> > >
> > > @@ -5466,11 +5501,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
> > > /* Decode instruction info and find the field to read */
> > > field = kvm_register_read(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
> > > /* Read the field, zero-extended to a u64 field_value */
> > > - if (!vmcs12_read_any(vcpu, field, &field_value)) {
> > > - nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > - skip_emulated_instruction(vcpu);
> > > - return 1;
> > > - }
> > > + field_value = vmcs12_read(vcpu, field);
> > You do not handle failure here and always write back field_value even if
> > vmcs12_read() failed. Actually now it is impossible to detect a failure.
> > Call to
> > nested_vmx_failValid() in vmcs12_read() will be overwritten by call to
> > nested_vmx_succeed() at the end of
> > handle_vmread() and skip_emulated_instruction() will be called twice.
>
> Thanks Gleb and Orit to raise this issue.
>
> What about moving the offset check outside the vmcs12_read() and
> vmcs12_write() function, and put it directly in handle_vmread() and
> handle_vmwrite()?
> I think we only need to do offset error check in handle_vmread() and
> handle_vmwrite() since they are to emulate correct behavior for guest VMM.
> For example, if guest VMM reads a field that is not valid or writes a field
> that is read only, then in emulation code handle_vmread() and handle_vmwrite,
> we need to raise error to guest VMM.
> For other calling of vmcs12_read() and vmcs12_write() functions in KVM
> hypervisor (see PATCH 3/4), actually the caller needs to ensure the field
> should be valid. Otherwise it is a bug in KVM hypervisor itself.
> Does it make sense? If so, I will revise this patch according to above.
>
Yes, it makes sense.
> Thanks,
> Dongxiao
>
> >
> > > + skip_emulated_instruction(vcpu);
> >
> > > /*
> > > * Now copy part of this value to register or memory, as requested.
> > > * Note that the number of bits actually copied is 32 or 64
> > > depending @@ -5500,8 +5531,6 @@ static int handle_vmwrite(struct
> > kvm_vcpu *vcpu)
> > > gva_t gva;
> > > unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
> > > u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
> > > - char *p;
> > > - short offset;
> > > /* The value to write might be 32 or 64 bits, depending on L1's long
> > > * mode, and eventually we need to write that into a field of several
> > > * possible lengths. The code below first zero-extends the value to
> > > 64 @@ -5537,33 +5566,8 @@ static int handle_vmwrite(struct kvm_vcpu
> > *vcpu)
> > > skip_emulated_instruction(vcpu);
> > > return 1;
> > > }
> > > -
> > > - offset = vmcs_field_to_offset(field);
> > > - if (offset < 0) {
> > > - nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > - skip_emulated_instruction(vcpu);
> > > - return 1;
> > > - }
> > > - p = ((char *) get_vmcs12(vcpu)) + offset;
> > > -
> > > - switch (vmcs_field_type(field)) {
> > > - case VMCS_FIELD_TYPE_U16:
> > > - *(u16 *)p = field_value;
> > > - break;
> > > - case VMCS_FIELD_TYPE_U32:
> > > - *(u32 *)p = field_value;
> > > - break;
> > > - case VMCS_FIELD_TYPE_U64:
> > > - *(u64 *)p = field_value;
> > > - break;
> > > - case VMCS_FIELD_TYPE_NATURAL_WIDTH:
> > > - *(natural_width *)p = field_value;
> > > - break;
> > > - default:
> > > - nested_vmx_failValid(vcpu,
> > VMXERR_UNSUPPORTED_VMCS_COMPONENT);
> > > - skip_emulated_instruction(vcpu);
> > > + if (!vmcs12_write(vcpu, field, field_value))
> > > return 1;
> > > - }
> > >
> > > nested_vmx_succeed(vcpu);
> > > skip_emulated_instruction(vcpu);
> > > --
> > > 1.7.1
> >
> > --
> > Gleb.
--
Gleb.
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