Re: [Xen-devel] [PATCH] x86-64: drop updating of UREGS_rip when converting sysenter to #GP

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-07-26 at 16:10 +0100, Jan Beulich wrote:
> This was set to zero immediately before the #GP injection code, since
> SYSENTER doesn't really have a return address.
> 
> Reported-by: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> 
> Furthermore, UREGS_cs and UREGS_rip don't need to be written a second
> time, as the PUSHes above already can/do take care of putting in place
> the intended values.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I'd totally forgotten about this, but 

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

> 
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -275,15 +275,13 @@ ENTRY(sysenter_entry)
>          pushfq
>          .globl sysenter_eflags_saved
>  sysenter_eflags_saved:
> -        pushq $0
> -        pushq $0
> +        pushq $3 /* ring 3 null cs */
> +        pushq $0 /* null rip */
>          pushq $0
>          movl  $TRAP_syscall,4(%rsp)
>          SAVE_ALL
>          GET_CURRENT(%rbx)
>          cmpb  $0,VCPU_sysenter_disables_events(%rbx)
> -        movq  $0,UREGS_rip(%rsp) /* null rip */
> -        movl  $3,UREGS_cs(%rsp)  /* ring 3 null cs */
>          movq  VCPU_sysenter_addr(%rbx),%rax
>          setne %cl
>          leaq  VCPU_trap_bounce(%rbx),%rdx
> @@ -292,7 +290,6 @@ sysenter_eflags_saved:
>  UNLIKELY_START(z, sysenter_gpf)
>          movq  VCPU_trap_ctxt(%rbx),%rsi
>          movl  $TRAP_gp_fault,UREGS_entry_vector(%rsp)
> -        subq  $2,UREGS_rip(%rsp)
>          movl  %eax,TRAPBOUNCE_error_code(%rdx)
>          movq  TRAP_gp_fault * TRAPINFO_sizeof + TRAPINFO_eip(%rsi),%rax
>          testb $4,TRAP_gp_fault * TRAPINFO_sizeof + TRAPINFO_flags(%rsi)
> 
> 
> 



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