Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200915172658.1432732-1-rkir@google.com> <20200915174643.GT14436@zn.tnic>
In-Reply-To: <20200915174643.GT14436@zn.tnic>
From:   Roman Kiryanov <rkir@google.com>
Date:   Tue, 15 Sep 2020 10:57:16 -0700
Message-ID: <CAOGAQepp_1QXrNAAXbLpW8qrujfdszfU2rMoh804wKK-Ja66Yw@mail.gmail.com>
Subject: Re: [PATCH] arch: x86: power: cpu: init %gs before
 __restore_processor_state (clang)
To:     Borislav Petkov <bp@alien8.de>
Cc:     rjw@rjwysocki.net, pavel@ucw.cz,
        Thomas Gleixner <tglx@linutronix.de>, mingo@redhat.com,
        x86@kernel.org, linux-pm@vger.kernel.org,
        Greg KH <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Alistair Delva <adelva@google.com>,
        Haitao Shan <hshan@google.com>,
        lkml <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Sep 15, 2020 at 10:46 AM Borislav Petkov <bp@alien8.de> wrote:

Hi Borislav, thank you for a quick response.

> Ok, google guys, pls make sure you Cc LKML too as this is where *all*
> patches and discussions are archived. Adding it now to Cc.

Thank you, I did not know this.

> Ok, so why is the kernel supposed to take yet another ugly workaround
> because there's a bug in the compiler?

I believe the kernel makes a questionable assumption on how clang
uses registers (gs will not be used if stack protection is disabled).
Both kernel and clang behaves unfortunate here.

> disable LTO

CFI depends on LTO.