> -----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.
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.
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