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Date: Tue, 6 Aug 2019 10:30:32 +0200
From: Peter Zijlstra <>
To: Borislav Petkov <>
Cc: Thomas Garnier <>,
	Kernel Hardening <>,
	Kristen Carlson Accardi <>,
	Kees Cook <>,
	Andy Lutomirski <>,
	Thomas Gleixner <>,
	Ingo Molnar <>, "H. Peter Anvin" <>,
	the arch/x86 maintainers <>,
	LKML <>
Subject: Re: [PATCH v9 04/11] x86/entry/64: Adapt assembly for PIE support

On Tue, Aug 06, 2019 at 07:08:51AM +0200, Borislav Petkov wrote:
> On Mon, Aug 05, 2019 at 10:50:30AM -0700, Thomas Garnier wrote:
> > I saw that %rdx was used for temporary usage and restored before the
> > end so I assumed that it was not an option.
> PUSH_AND_CLEAR_REGS saves all regs earlier so I think you should be
> able to use others. Like SAVE_AND_SWITCH_TO_KERNEL_CR3/RESTORE_CR3, for
> example, uses %r15 and %r14.

AFAICT the CONFIG_DEBUG_ENTRY thing he's changing is before we setup

Also consider the UNWIND hint that's in there, it states we only have
the IRET frame on stack, not a full regs set.

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