Re: [Xen-devel] [PATCH 1/1 V4] x86/AMD: Fix nested svm crash due to assertion in __virt_to_maddr

[Tim Deegan <tim@xxxxxxx>]

Hi,

At 16:46 -0500 on 26 Jul (1374857167), suravee.suthikulpanit@xxxxxxx wrote:
> From: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> 
> Fix assertion in __virt_to_maddr when starting nested SVM guest
> in debug mode. Investigation has shown that svm_vmsave/svm_vmload
> make use of __pa() with invalid address.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>

This looks much better, but I have a few comments still:

> +static struct page_info *
> +_get_vmcb_page(struct domain *d, uint64_t vmcbaddr)

Can you give this a name that makes it clearer that it's for nested
VMCBs and not part of the handling of 'real' VMCBs?  Also, please drop
the leading underscore.

> +{
> +    struct page_info *page;
> +    p2m_type_t p2mt;
> +
> +    page = get_page_from_gfn(d, vmcbaddr >> PAGE_SHIFT, 
> +                            &p2mt, P2M_ALLOC | P2M_UNSHARE);
> +    
> +    if (!page)

Missing whitespace.

> +        return NULL;
> +
> +    if ( !p2m_is_ram(p2mt) || p2m_is_readonly(p2mt) )
> +    {
> +        put_page(page);
> +        return NULL; 
> +    }
> +
> +    return  page;
> +}
> +
>  static void
>  svm_vmexit_do_vmload(struct vmcb_struct *vmcb,
>                       struct cpu_user_regs *regs,
> @@ -1802,6 +1823,7 @@ svm_vmexit_do_vmload(struct vmcb_struct *vmcb,
>  {
>      int ret;
>      unsigned int inst_len;
> +    struct page_info *page;
>      struct nestedvcpu *nv = &vcpu_nestedhvm(v);
>  
>      if ( (inst_len = __get_instruction_length(v, INSTR_VMLOAD)) == 0 )
> @@ -1819,7 +1841,19 @@ svm_vmexit_do_vmload(struct vmcb_struct *vmcb,
>          goto inject;
>      }
>  
> -    svm_vmload(nv->nv_vvmcx);
> +    /* Need to translate L1-GPA to MPA */
> +    page = _get_vmcb_page(v->domain, nv->nv_vvmcxaddr);
> +    if (!page)

Whitespace.

> +    {
> +        gdprintk(XENLOG_ERR,
> +            "VMLOAD: mapping vmcb L1-GPA to MPA failed, injecting #UD\n");
> +        ret = TRAP_invalid_op;

The documentation for VMLOAD suggests TRAP_gp_fault for this case.

> +        goto inject;
> +    }
> +
> +    svm_vmload_pa(page_to_mfn(page) << PAGE_SHIFT);

Please use page_to_maddr() for this. 

> +    put_page(page);
> +
>      /* State in L1 VMCB is stale now */
>      v->arch.hvm_svm.vmcb_in_sync = 0;
>  
> @@ -1838,6 +1872,7 @@ svm_vmexit_do_vmsave(struct vmcb_struct *vmcb,
>  {
>      int ret;
>      unsigned int inst_len;
> +    struct page_info *page;
>      struct nestedvcpu *nv = &vcpu_nestedhvm(v);
>  
>      if ( (inst_len = __get_instruction_length(v, INSTR_VMSAVE)) == 0 )
> @@ -1855,8 +1890,18 @@ svm_vmexit_do_vmsave(struct vmcb_struct *vmcb,
>          goto inject;
>      }
>  
> -    svm_vmsave(nv->nv_vvmcx);
> +    /* Need to translate L1-GPA to MPA */
> +    page = _get_vmcb_page(v->domain, nv->nv_vvmcxaddr);
> +    if (!page)

Whitespace.

> +    {
> +        gdprintk(XENLOG_ERR,
> +            "VMSAVE: mapping vmcb L1-GPA to MPA failed, injecting #UD\n");
> +        ret = TRAP_invalid_op;
> +        goto inject;
> +    }
>  
> +    svm_vmsave_pa(page_to_mfn(page) << PAGE_SHIFT);

Again, #GP, and page_to_maddr().

Thanks, 

Tim.

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