Re: [PATCH 07/28] nVMX: Decoding memory operands of VMX instructions

[Avi Kivity <avi@redhat.com>]

On 12/08/2010 07:03 PM, Nadav Har'El wrote:
> This patch includes a utility function for decoding pointer operands of VMX
> instructions issued by L1 (a guest hypervisor)
>
> Signed-off-by: Nadav Har'El<nyh@il.ibm.com>
> ---
>   arch/x86/kvm/vmx.c |   59 +++++++++++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/x86.c |    3 +-
>   arch/x86/kvm/x86.h |    3 ++
>   3 files changed, 64 insertions(+), 1 deletion(-)
>
> --- .before/arch/x86/kvm/x86.c	2010-12-08 18:56:49.000000000 +0200
> +++ .after/arch/x86/kvm/x86.c	2010-12-08 18:56:49.000000000 +0200
> @@ -3688,7 +3688,7 @@ static int kvm_fetch_guest_virt(gva_t ad
>   					  exception);
>   }
>
> -static int kvm_read_guest_virt(gva_t addr, void *val, unsigned int bytes,
> +int kvm_read_guest_virt(gva_t addr, void *val, unsigned int bytes,
>   			       struct kvm_vcpu *vcpu,
>   			       struct x86_exception *exception)
>   {
> @@ -3696,6 +3696,7 @@ static int kvm_read_guest_virt(gva_t add
>   	return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access,
>   					  exception);
>   }
> +EXPORT_SYMBOL_GPL(kvm_read_guest_virt);
>
>   static int kvm_read_guest_virt_system(gva_t addr, void *val, unsigned int bytes,
>   				      struct kvm_vcpu *vcpu,
> --- .before/arch/x86/kvm/x86.h	2010-12-08 18:56:49.000000000 +0200
> +++ .after/arch/x86/kvm/x86.h	2010-12-08 18:56:49.000000000 +0200
> @@ -74,6 +74,9 @@ void kvm_before_handle_nmi(struct kvm_vc
>   void kvm_after_handle_nmi(struct kvm_vcpu *vcpu);
>   int kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq);
>
> +int kvm_read_guest_virt(gva_t addr, void *val, unsigned int bytes,
> +		struct kvm_vcpu *vcpu, struct x86_exception *exception);
> +
>   void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data);
>
>   #endif
> --- .before/arch/x86/kvm/vmx.c	2010-12-08 18:56:49.000000000 +0200
> +++ .after/arch/x86/kvm/vmx.c	2010-12-08 18:56:49.000000000 +0200
> @@ -3936,6 +3936,65 @@ static int handle_vmoff(struct kvm_vcpu
>   }
>
>   /*
> + * Decode the memory-address operand of a vmx instruction, as recorded on an
> + * exit caused by such an instruction (run by a guest hypervisor).
> + * On success, returns 0. When the operand is invalid, returns 1 and throws
> + * #UD or #GP.
> + */
> +static int get_vmx_mem_address(struct kvm_vcpu *vcpu,
> +				 unsigned long exit_qualification,
> +				 u32 vmx_instruction_info, gva_t *ret)
> +{
> +	/*
> +	 * According to Vol. 3B, "Information for VM Exits Due to Instruction
> +	 * Execution", on an exit, vmx_instruction_info holds most of the
> +	 * addressing components of the operand. Only the displacement part
> +	 * is put in exit_qualification (see 3B, "Basic VM-Exit Information").
> +	 * For how an actual address is calculated from all these components,
> +	 * refer to Vol. 1, "Operand Addressing".
> +	 */
> +	int  scaling = vmx_instruction_info&  3;
> +	int  addr_size = (vmx_instruction_info>>  7)&  7;
> +	bool is_reg = vmx_instruction_info&  (1u<<  10);
> +	int  seg_reg = (vmx_instruction_info>>  15)&  7;
> +	int  index_reg = (vmx_instruction_info>>  18)&  0xf;
> +	bool index_is_valid = !(vmx_instruction_info&  (1u<<  22));
> +	int  base_reg       = (vmx_instruction_info>>  23)&  0xf;
> +	bool base_is_valid  = !(vmx_instruction_info&  (1u<<  27));
> +
> +	if (is_reg) {
> +		kvm_queue_exception(vcpu, UD_VECTOR);
> +		return 1;
> +	}
> +
> +	switch (addr_size) {
> +	case 1: /* 32 bit. high bits are undefined according to the spec: */
> +		exit_qualification&= 0xffffffff;

Best to do this at the end, on *ret, so that segment base + offset is 
subject to truncation.

> +		break;
> +	case 2: /* 64 bit */
> +		break;
> +	default: /* 16 bit */
> +		return 1;
> +	}
> +
> +	/* Addr = segment_base + offset */
> +	/* offset = base + [index * scale] + displacement */
> +	*ret = vmx_get_segment_base(vcpu, seg_reg);
> +	if (base_is_valid)
> +		*ret += kvm_register_read(vcpu, base_reg);
> +	if (index_is_valid)
> +		*ret += kvm_register_read(vcpu, index_reg)<<scaling;
> +	*ret += exit_qualification; /* holds the displacement */
> +	/*
> +	 * TODO: throw #GP (and return 1) in various cases that the VM*
> +	 * instructions require it - e.g., offset beyond segment limit,
> +	 * unusable or unreadable/unwritable segment, non-canonical 64-bit
> +	 * address, and so on. Currently these are not checked.
> +	 */
> +	return 0;
> +}
> +

-- 
error compiling committee.c: too many arguments to function