Re: [PATCH] x86/entry/64: Fix CR3 restore order in paranoid_exit()

[Thomas Gleixner]

On Wed, 14 Feb 2018, Ingo Molnar wrote:
> * Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> 
> > On 02/13/2018 06:27 PM, Josh Poimboeuf wrote:
> > > --- a/arch/x86/entry/entry_64.S
> > > +++ b/arch/x86/entry/entry_64.S
> > > @@ -1167,10 +1167,10 @@ ENTRY(paranoid_exit)
> > >  	UNWIND_HINT_REGS
> > >  	DISABLE_INTERRUPTS(CLBR_ANY)
> > >  	TRACE_IRQS_OFF_DEBUG
> > > +	RESTORE_CR3	scratch_reg=%r15 save_reg=%r14
> > >  	testl	%ebx, %ebx			/* swapgs needed? */
> > >  	jnz	.Lparanoid_exit_no_swapgs
> > >  	TRACE_IRQS_IRETQ
> > > -	RESTORE_CR3	scratch_reg=%rbx save_reg=%r14
> > >  	SWAPGS_UNSAFE_STACK
> > >  	jmp	.Lparanoid_exit_restore
> > >  .Lparanoid_exit_no_swapgs:
> > 
> > TRACE_IRQS_* call non-entry functions that are not mapped by the user
> > CR3.  How can this possibly work?  What am I missing?
> 
> How about something like the patch below? (Totally untested)

But correct ....


> Thanks,
> 
> 	Ingo
> ---
>  arch/x86/entry/entry_64.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index cd216c9431e1..8971bd64d515 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1175,6 +1175,7 @@ ENTRY(paranoid_exit)
>  	jmp	.Lparanoid_exit_restore
>  .Lparanoid_exit_no_swapgs:
>  	TRACE_IRQS_IRETQ_DEBUG
> +	RESTORE_CR3	scratch_reg=%rbx save_reg=%r14
>  .Lparanoid_exit_restore:
>  	jmp restore_regs_and_return_to_kernel
>  END(paranoid_exit)
>