Re: [PATCH v2 5/8] x86/iommu: the code addressing CVE-2011-1898 is VT-d specific

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.01.2023 09:44, Xenia Ragiadakou wrote:
> The variable untrusted_msi indicates whether the system is vulnerable to
> CVE-2011-1898. This vulnerablity is VT-d specific.

As per the reply by Andrew to v1, this vulnerability is generic to intremap-
incapable or intremap-disabled configurations. You want to say so. In turn
I wonder whether instead of the changes you're making you wouldn't want to
move the definition of the variable to xen/drivers/passthrough/x86/iommu.c.
A useful further step might be to guard its definition (not necessarily
its declaration; see replies to earlier patches) by CONFIG_PV instead (of
course I understand that's largely orthogonal to your series here, yet it
would fit easily with moving the definition).

> --- a/xen/arch/x86/include/asm/iommu.h
> +++ b/xen/arch/x86/include/asm/iommu.h
> @@ -127,7 +127,9 @@ int iommu_identity_mapping(struct domain *d, p2m_access_t 
> p2ma,
>                             unsigned int flag);
>  void iommu_identity_map_teardown(struct domain *d);
>  
> +#ifdef CONFIG_INTEL_IOMMU
>  extern bool untrusted_msi;
> +#endif

As per above / earlier comments I don't think this part is needed in any
event.

> --- a/xen/arch/x86/pv/hypercall.c
> +++ b/xen/arch/x86/pv/hypercall.c
> @@ -193,8 +193,10 @@ void pv_ring1_init_hypercall_page(void *p)
>  
>  void do_entry_int82(struct cpu_user_regs *regs)
>  {
> +#ifdef CONFIG_INTEL_IOMMU
>      if ( unlikely(untrusted_msi) )
>          check_for_unexpected_msi((uint8_t)regs->entry_vector);
> +#endif
>  
>      _pv_hypercall(regs, true /* compat */);
>  }
> diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
> index ae01285181..8f2fb36770 100644
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -406,11 +406,13 @@ ENTRY(int80_direct_trap)
>  .Lint80_cr3_okay:
>          sti
>  
> +#ifdef CONFIG_INTEL_IOMMU
>          cmpb  $0,untrusted_msi(%rip)
>  UNLIKELY_START(ne, msi_check)
>          movl  $0x80,%edi
>          call  check_for_unexpected_msi
>  UNLIKELY_END(msi_check)
> +#endif
>  
>          movq  STACK_CPUINFO_FIELD(current_vcpu)(%rbx), %rbx
>