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SubjectRe: [PATCH] x86/entry/64: Fix CR3 restore order in paranoid_exit()
On Wed, 14 Feb 2018, Ingo Molnar wrote:
> * Dave Hansen <dave.hansen@intel.com> 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)
>

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