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Message-ID: <20190806083032.GN2332@hirez.programming.kicks-ass.net>
Date: Tue, 6 Aug 2019 10:30:32 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Garnier <thgarnie@...omium.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Kristen Carlson Accardi <kristen@...ux.intel.com>,
Kees Cook <keescook@...omium.org>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
the arch/x86 maintainers <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
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
pt_regs.
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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