Re: [Xen-devel] [PATCH v2] Fix the mistake for #DB and #OF exception

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Monday, May 14, 2012 4:05 PM
> To: Hao, Xudong
> Cc: Keir Fraser(keir.xen@xxxxxxxxx); Dong, Eddie; Nakajima, Jun; Zhang,
> Xiantao; xen-devel(xen-devel@xxxxxxxxxxxxx); Aravindh Puthiyaparambil
> Subject: Re: [PATCH v2] Fix the mistake for #DB and #OF exception
> 
> >>> On 12.05.12 at 11:12, "Hao, Xudong" <xudong.hao@xxxxxxxxx> wrote:
> > Fix the mistake for debug exception(#DB; generated by INT1), overflow
> > exception(#OF; generated by INTO) and int n instruction emulation.
> >
> > #DB should use hardware exception(except #DB generated by opcode 0xf1),
> #OF
> > should use software exception, which int n instruction should use software
> > interrupt.
> >
> > Signed-off-by: Eddie Dong<eddie.dong@xxxxxxxxx>
> > Signed-off-by: Xudong Hao <xudong.hao@xxxxxxxxx>
> >
> > diff -r cd4dd23a831d xen/arch/x86/hvm/vmx/vmx.c
> > --- a/xen/arch/x86/hvm/vmx/vmx.c    Fri May 11 18:59:07 2012 +0100
> > +++ b/xen/arch/x86/hvm/vmx/vmx.c    Mon May 13 01:01:24 2013 +0800
> > @@ -1350,6 +1350,14 @@ static void __vmx_inject_exception(int t
> >          curr->arch.hvm_vmx.vmx_emulate = 1;
> >  }
> >
> > +/*
> > + * Generate the virtual event to guest.
> > + * NOTE:
> > + *    This is for processor execution generated exceptions,
> > + * and INT 3(CC), INTO (CE) instruction emulation. INT3 and
> > + * INT0 use software exception, and INT n should use
> 
> INTO ...
> 
> > + * software interrupt.
> > + */
> 
> Neither comment nor description still say anything about what needs
> to be fixed going forward (namely the need to properly handle INT nn
> when nn < 0x20).
> 
> >  void vmx_inject_hw_exception(int trap, int error_code)
> >  {
> >      unsigned long intr_info;
> > @@ -1365,7 +1373,6 @@ void vmx_inject_hw_exception(int trap, i
> >      switch ( trap )
> >      {
> >      case TRAP_debug:
> > -        type = X86_EVENTTYPE_SW_EXCEPTION;
> >          if ( guest_cpu_user_regs()->eflags & X86_EFLAGS_TF )
> >          {
> >              __restore_debug_registers(curr);
> 
> While the description correctly mentions the opcode 0xf1 case, the
> code makes no attempt at dealing with it. At least a comment would
> seem appropriate here, indicating the need for further adjustment.
> 
> > @@ -1387,10 +1394,15 @@ void vmx_inject_hw_exception(int trap, i
> >          __vmwrite(VM_ENTRY_INSTRUCTION_LEN, 1); /* int3 */
> >          break;
> >
> > +    case TRAP_overflow:
> > +        type = X86_EVENTTYPE_SW_EXCEPTION;
> > +        __vmwrite(VM_ENTRY_INSTRUCTION_LEN, 1); /* into */
> 
> So you're adding one more of these incorrect length settings. This
> is particularly harmful here, as iirc some gcc versions generate
> 2-byte INT 4 instructions in certain overflow checking functions.
> 
> As this needs to be taken care of here anyway, we should aim at
> fixing it for the other code paths too (as I just saw Eddie also
> suggests).
> 

I will clean this patch only for fixing the mistake of int3, #DB and #OF just 
as Eddie's suggestion.

> Jan
> 
> > +        break;
> > +
> >      default:
> >          if ( trap > TRAP_last_reserved )
> >          {
> > -            type = X86_EVENTTYPE_SW_EXCEPTION;
> > +            type = X86_EVENTTYPE_SW_INTERRUPT;
> >              __vmwrite(VM_ENTRY_INSTRUCTION_LEN, 2); /* int imm8
> */
> >          }
> >          break;
> 
> 


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