Re: [PATCH v2 3/4] KVM: x86: check CS.DPL against RPL during task switch

[Wei Huang]

On Sat, May 24, 2014 at 1:12 PM, Wei Huang <huangwei.virt@xxxxxxxxx> wrote:
> Table 7-1 of the SDM mentions a check that the code segment's
> DPL must match the selector's RPL.  This was not done by KVM,
> fix it.
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>  arch/x86/kvm/emulate.c | 31 +++++++++++++++++--------------
>  1 file changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 47e716ef46b7..2fa7ab069817 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -1411,7 +1411,7 @@ static int write_segment_descriptor(struct
> x86_emulate_ctxt *ctxt,
>
>  /* Does not support long mode */
>  static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
> -     u16 selector, int seg, u8 cpl)
> +     u16 selector, int seg, u8 cpl, bool in_task_switch)

A small nit-picking: a new line to comply with 80 characters per line
rule. otherwise looks good to me.

Reviewed-by: Wei Huang <huangwei.virt@xxxxxxxxx>

>  {
>   struct desc_struct seg_desc, old_desc;
>   u8 dpl, rpl;
> @@ -1486,6 +1486,9 @@ static int __load_segment_descriptor(struct
> x86_emulate_ctxt *ctxt,
>   goto exception;
>   break;
>   case VCPU_SREG_CS:
> + if (in_task_switch && rpl != dpl)
> + goto exception;
> +
>   if (!(seg_desc.type & 8))
>   goto exception;
>
> @@ -1547,7 +1550,7 @@ static int load_segment_descriptor(struct
> x86_emulate_ctxt *ctxt,
>     u16 selector, int seg)
>  {
>   u8 cpl = ctxt->ops->cpl(ctxt);
> - return __load_segment_descriptor(ctxt, selector, seg, cpl);
> + return __load_segment_descriptor(ctxt, selector, seg, cpl, false);
>  }
>
>  static void write_register_operand(struct operand *op)
> @@ -2440,19 +2443,19 @@ static int load_state_from_tss16(struct
> x86_emulate_ctxt *ctxt,
>   * Now load segment descriptors. If fault happens at this stage
>   * it is handled in a context of new task
>   */
> - ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
>
> @@ -2577,25 +2580,25 @@ static int load_state_from_tss32(struct
> x86_emulate_ctxt *ctxt,
>   * Now load segment descriptors. If fault happenes at this stage
>   * it is handled in a context of new task
>   */
> - ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->ldt_selector,
> VCPU_SREG_LDTR, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
> - ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl);
> + ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl, true);
>   if (ret != X86EMUL_CONTINUE)
>   return ret;
>
> --
> 1.8.3.1
>
>
> --
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