Re: [Xen-devel] [PATCH] x86-64: don't allow non-canonical addresses to be set for any callback

[Keir Fraser <keir@xxxxxxx>]

On 13/06/2012 11:02, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Rather than deferring the detection of these to the point where they
> get actually used (the fix for XSA-7, 25480:76eaf5966c05, causing a #GP
> to be raised by IRET, which invokes the guest's [fragile] fail-safe
> callback), don't even allow such to be set.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -736,6 +736,14 @@ int arch_set_info_guest(
>      {
>          if ( !compat )
>          {
> +#ifdef __x86_64__
> +            if ( !is_canonical_address(c.nat->user_regs.eip) ||
> +                 !is_canonical_address(c.nat->event_callback_eip) ||
> +                 !is_canonical_address(c.nat->syscall_callback_eip) ||
> +                 !is_canonical_address(c.nat->failsafe_callback_eip) )
> +                return -EINVAL;
> +#endif
> +
>              fixup_guest_stack_selector(d, c.nat->user_regs.ss);
>              fixup_guest_stack_selector(d, c.nat->kernel_ss);
>              fixup_guest_code_selector(d, c.nat->user_regs.cs);
> @@ -745,7 +753,11 @@ int arch_set_info_guest(
>  #endif
>  
>              for ( i = 0; i < 256; i++ )
> +            {
> +                if ( !is_canonical_address(c.nat->trap_ctxt[i].address) )
> +                    return -EINVAL;
>                  fixup_guest_code_selector(d, c.nat->trap_ctxt[i].cs);
> +            }
>  
>              /* LDT safety checks. */
>              if ( ((c.nat->ldt_base & (PAGE_SIZE-1)) != 0) ||
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -1033,6 +1033,9 @@ long arch_do_domctl(
>  #ifdef __x86_64__
>              if ( !is_hvm_domain(d) )
>              {
> +                if ( !is_canonical_address(evc->sysenter_callback_eip) ||
> +                     !is_canonical_address(evc->syscall32_callback_eip) )
> +                    goto ext_vcpucontext_out;
>                  fixup_guest_code_selector(d, evc->sysenter_callback_cs);
>                  v->arch.pv_vcpu.sysenter_callback_cs      =
>                      evc->sysenter_callback_cs;
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -3581,6 +3581,9 @@ long register_guest_nmi_callback(unsigne
>      struct domain *d = v->domain;
>      struct trap_info *t = &v->arch.pv_vcpu.trap_ctxt[TRAP_nmi];
>  
> +    if ( !is_canonical_address(address) )
> +        return -EINVAL;
> +
>      t->vector  = TRAP_nmi;
>      t->flags   = 0;
>      t->cs      = (is_pv_32on64_domain(d) ?
> @@ -3708,6 +3711,9 @@ long do_set_trap_table(XEN_GUEST_HANDLE(
>          if ( cur.address == 0 )
>              break;
>  
> +        if ( !is_canonical_address(cur.address) )
> +            return -EINVAL;
> +
>          fixup_guest_code_selector(curr->domain, cur.cs);
>  
>          memcpy(&dst[cur.vector], &cur, sizeof(cur));
> 
> 
> 
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