linux-kernel - Re: [PATCH] arch: x86: power: cpu: init %gs before __restore_processor

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Message-ID: <CAOGAQepp_1QXrNAAXbLpW8qrujfdszfU2rMoh804wKK-Ja66Yw@mail.gmail.com>
Date:   Tue, 15 Sep 2020 10:57:16 -0700
From:   Roman Kiryanov <rkir@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     rjw@...ysocki.net, pavel@....cz,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        x86@...nel.org, linux-pm@...r.kernel.org,
        Greg KH <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alistair Delva <adelva@...gle.com>,
        Haitao Shan <hshan@...gle.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arch: x86: power: cpu: init %gs before
 __restore_processor_state (clang)

On Tue, Sep 15, 2020 at 10:46 AM Borislav Petkov <bp@...en8.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.