linux-kernel - Re: [PATCH] KVM: x86: Fix CR3 and LDT sel should not be saved in TSS

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Message-ID: <20140416192041.GC8773@amt.cnet>
Date:	Wed, 16 Apr 2014 16:20:41 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>
Cc:	gleb@...nel.org, pbonzini@...hat.com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Fix CR3 and LDT sel should not be saved in TSS

On Mon, Apr 07, 2014 at 06:37:47PM +0300, Nadav Amit wrote:
> According to Intel specifications, only general purpose registers and segment
> selectors should are saved in the old TSS during 32-bit task-switch.

should be

> Signed-off-by: Nadav Amit <namit@...technion.ac.il>
> ---
>  arch/x86/kvm/emulate.c |   10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 205b17e..0dec502 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2496,7 +2496,7 @@ static int task_switch_16(struct x86_emulate_ctxt *ctxt,
>  static void save_state_to_tss32(struct x86_emulate_ctxt *ctxt,
>  				struct tss_segment_32 *tss)
>  {
> -	tss->cr3 = ctxt->ops->get_cr(ctxt, 3);
> +	/* CR3 and ldt selector are not saved intentionally */
>  	tss->eip = ctxt->_eip;
>  	tss->eflags = ctxt->eflags;
>  	tss->eax = reg_read(ctxt, VCPU_REGS_RAX);
> @@ -2514,7 +2514,6 @@ static void save_state_to_tss32(struct x86_emulate_ctxt *ctxt,
>  	tss->ds = get_segment_selector(ctxt, VCPU_SREG_DS);
>  	tss->fs = get_segment_selector(ctxt, VCPU_SREG_FS);
>  	tss->gs = get_segment_selector(ctxt, VCPU_SREG_GS);
> -	tss->ldt_selector = get_segment_selector(ctxt, VCPU_SREG_LDTR);
>  }
>  
>  static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,

Only this hunk is enough ?

> @@ -2604,6 +2603,8 @@ static int task_switch_32(struct x86_emulate_ctxt *ctxt,
>  	struct tss_segment_32 tss_seg;
>  	int ret;
>  	u32 new_tss_base = get_desc_base(new_desc);
> +	u32 eip_offset = offsetof(struct tss_segment_32, eip);
> +	u32 ldt_sel_offset = offsetof(struct tss_segment_32, ldt_selector);
>  
>  	ret = ops->read_std(ctxt, old_tss_base, &tss_seg, sizeof tss_seg,
>  			    &ctxt->exception);
> @@ -2613,8 +2614,9 @@ static int task_switch_32(struct x86_emulate_ctxt *ctxt,
>  
>  	save_state_to_tss32(ctxt, &tss_seg);
>  
> -	ret = ops->write_std(ctxt, old_tss_base, &tss_seg, sizeof tss_seg,
> -			     &ctxt->exception);
> +	/* Only GP registers and segment selectors are saved */
> +	ret = ops->write_std(ctxt, old_tss_base + eip_offset, &tss_seg.eip,
> +			     ldt_sel_offset - eip_offset, &ctxt->exception);
>  	if (ret != X86EMUL_CONTINUE)
>  		/* FIXME: need to provide precise fault address */
>  		return ret;
> -- 
> 1.7.10.4
> 
> --
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