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

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Date:   Tue, 15 Sep 2020 11:36:13 -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 11:27 AM Borislav Petkov <bp@...en8.de> wrote:
> > 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.
>
> If the kernel is at fault here and this same thing happens with GCC,
> sure, but this is a clang-specific fix.

This is fair. Unfortunately I am not an x86 asm expert. I expect the proper
fix should land into arch/x86/kernel/acpi/wakeup_64.S to init %gs
(maybe some more registers) before "jmp restore_processor_state".

Regards,
Roman.