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From: Roman Kiryanov <rkir@google.com>
To: Pavel Machek <pavel@denx.de>
Cc: Borislav Petkov <bp@alien8.de>,
	rjw@rjwysocki.net, 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>
Subject: Re: [PATCH] arch: x86: power: cpu: init %gs before __restore_processor_state (clang)
Date: Mon, 21 Sep 2020 16:28:57 -0700	[thread overview]
Message-ID: <CAOGAQepVWwMvA_m_kZpwQ4UN+ziR+=w2auiL1euFyuGvyCU7SQ@mail.gmail.com> (raw)
In-Reply-To: <20200918222531.GD7443@duo.ucw.cz>

On Fri, Sep 18, 2020 at 3:25 PM Pavel Machek <pavel@denx.de> wrote:
>
> On Tue 2020-09-15 11:36:13, Roman Kiryanov wrote:
> > On Tue, Sep 15, 2020 at 11:27 AM Borislav Petkov <bp@alien8.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".
>
> That would certainly be nicer / more acceptable solution than patch
> being proposed here.
>
> Code was written with assumption compiler random C code would not use
> %gs. If that's no longer true, fixing it in wakeup_64.S _with comments
> explaining what goes on_ might be solution.

I looked and restore_processor_state is referenced in several places,
so changing
wakeup_64.S is not enough. Is moving the beginning of restore_processor_state
to an .S file ok? I see restore_processor_state initializes CR registers first,
do you know if there is a reason to do so (can I init segment
registers before CR ones)?

Regards,
Roman.

  reply	other threads:[~2020-09-21 23:29 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 17:26 [PATCH] arch: x86: power: cpu: init %gs before __restore_processor_state (clang) rkir
2020-09-15 17:46 ` Borislav Petkov
2020-09-15 17:57   ` Roman Kiryanov
2020-09-15 18:27     ` Borislav Petkov
2020-09-15 18:36       ` Roman Kiryanov
2020-09-15 18:52         ` Borislav Petkov
2020-09-15 18:55           ` Roman Kiryanov
2020-09-18 22:25         ` Pavel Machek
2020-09-21 23:28           ` Roman Kiryanov [this message]
2020-10-04  9:59             ` Pavel Machek
2020-09-15 18:00   ` Nick Desaulniers
2020-09-15 18:25     ` Borislav Petkov
2020-09-15 19:51       ` Nick Desaulniers
2020-09-15 20:20         ` Borislav Petkov
2020-09-15 21:49           ` Nick Desaulniers
2020-09-16  9:23             ` Borislav Petkov
2020-09-19 16:48             ` Pavel Machek
2020-09-16  8:17         ` peterz
2020-09-15 20:44     ` Arvind Sankar
2020-09-15 22:17 ` Pavel Machek
2020-09-15 22:21   ` Nick Desaulniers
2020-09-18 22:20     ` Pavel Machek
2020-09-15 23:13   ` Roman Kiryanov

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