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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