linux-kernel - Re: [PATCH V2] x86/boot: explicitly place .eh

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Date:   Mon, 18 Nov 2019 09:46:23 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Ilie Halip <ilie.halip@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH V2] x86/boot: explicitly place .eh_frame after .rodata

On Mon, Nov 18, 2019 at 6:36 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Wed, Nov 06, 2019 at 02:06:28PM +0200, Ilie Halip wrote:
> > diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld
> > index 0149e41d42c2..30ce52635cd0 100644
> > --- a/arch/x86/boot/setup.ld
> > +++ b/arch/x86/boot/setup.ld
> > @@ -25,6 +25,7 @@ SECTIONS
> >
> >       . = ALIGN(16);
> >       .rodata         : { *(.rodata*) }
> > +     .eh_frame       : { *(.eh_frame) }
>
> The kernel proper linker script does
>
>         /DISCARD/ : {
>                 *(.eh_frame)
>         }
>
> with the .eh_frame section.
>
> Wouldn't that solve your issue too, if you add it to the /DISCARD/
> section in that linker script too?

Yep. Looks like:
- arch/x86/kernel/vmlinux.lds.S
- arch/x86/realmode/rm/realmode.lds.S

discard .eh_frame, while
- arch/x86/entry/vdso/vdso-layout.lds.S
- arch/x86/um/vdso/vdso-layout.lds.S

keep it.  I assume then that just vdso code that get linked into
userspace needs to preserve this.  This suggestion would be a
functional change, which is why we pursued the conservative change
preserving it.
https://github.com/ClangBuiltLinux/linux/issues/760#issuecomment-549192213

Ilie, would you mind sending a v3 with Boris' recommendation?

-- 
Thanks,
~Nick Desaulniers