Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 6 Aug 2019 07:08:51 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Thomas Garnier <thgarnie@chromium.org>
Cc:     Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v9 04/11] x86/entry/64: Adapt assembly for PIE support
Message-ID: <20190806050851.GA25897@zn.tnic>
References: <20190730191303.206365-1-thgarnie@chromium.org>
 <20190730191303.206365-5-thgarnie@chromium.org>
 <20190805172854.GF18785@zn.tnic>
 <CAJcbSZGedSfZZ5rveH2+_3q7pvmMyDGLxmZU41Nno=ZBX8kN=w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAJcbSZGedSfZZ5rveH2+_3q7pvmMyDGLxmZU41Nno=ZBX8kN=w@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.