linux-kernel - Re: [PATCH] x86/entry/64: Fix CR3 restore order in paranoid

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Date:   Tue, 13 Feb 2018 20:19:53 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] x86/entry/64: Fix CR3 restore order in paranoid_exit()

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?