Re: [PATCH] arch: x86: power: cpu: init %gs before __restore_processor_state (clang)

[Pavel Machek]

On Tue 2020-09-15 11:36:13, Roman Kiryanov wrote:
> On Tue, Sep 15, 2020 at 11:27 AM Borislav Petkov <bp@xxxxxxxxx> 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.

Best regards,
									Pavel

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