linux-kernel - Re: Linux 5.8-rc1

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Message-ID: <20200616212536.GA1934393@rani.riverdale.lan>
Date:   Tue, 16 Jun 2020 17:25:36 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Gabriel C <nix.or.die@...glemail.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: Linux 5.8-rc1

On Tue, Jun 16, 2020 at 11:17:08PM +0200, Gabriel C wrote:
> Am Di., 16. Juni 2020 um 22:33 Uhr schrieb Arvind Sankar
> <nivedita@...m.mit.edu>:
> >
> > Can you attach the output of gcc -dumpspecs and gcc -v? I suspect your
> > compiler enables stack protector by default. My distro compiler does
> > that too, but not if -ffreestanding is enabled (which it is for the
> > purgatory).
> >
> 
> Files including config uploaded to there:
> 
> http://crazy.dev.frugalware.org/kernel/
> 

Yeah, your gcc doesn't have the -ffreestanding handling. Mine (from
gentoo) has this in the -dumpspecs output:

*cc1_options:
... %{nostdlib|nodefaultlibs|ffreestanding:-fno-stack-protector} ...

to switch off the default ssp when the standard libraries aren't available.

> > Does this patch help?
> >
> 
> I'll test in a bit and let you know.
> 
> > diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> > index b04e6e72a592..088bd764e0b7 100644
> > --- a/arch/x86/purgatory/Makefile
> > +++ b/arch/x86/purgatory/Makefile
> > @@ -34,6 +34,7 @@ KCOV_INSTRUMENT := n
> >  PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
> >  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
> >  PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
> > +PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
> >
> >  # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
> >  # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> 
> Thx.