linux-kernel - Re: [PATCH] x86: Discard .note.gnu.property sections in vDSO

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Date:   Fri, 27 Mar 2020 11:44:50 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH] x86: Discard .note.gnu.property sections in vDSO

On Thu, Mar 26, 2020 at 10:43:14AM -0700, H.J. Lu wrote:
> With the command-line option, -mx86-used-note=yes, the x86 assembler

I see:

       -mx86-used-note=no
       -mx86-used-note=yes
           These options control whether the assembler should generate
           GNU_PROPERTY_X86_ISA_1_USED and GNU_PROPERTY_X86_FEATURE_2_USED GNU property
           notes.  The default can be controlled by the --enable-x86-used-note
           configure option.

Is there a plan to use this build option in the kernel in the future or
all binutils will have it enabled or what's the story here?

Because I don't see -mx86-used-note used anywhere in the kernel...

> in binutils 2.32 and above generates a program property note in a note
> section, .note.gnu.property, to encode used x86 ISAs and features.  But
> x86 kernel vDSO linker script only contains a single NOTE segment:
> 
> PHDRS
> {
>  text PT_LOAD FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
>  dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
>  note PT_NOTE FLAGS(4); /* PF_R */
>  eh_frame_hdr 0x6474e550;
> }
> 
> The NOTE segment generated by vDSO linker script is aligned to 4 bytes.
> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
> we get
> 
> [hjl@...-skx-1 vdso]$ readelf -n vdso64.so
> 
> Displaying notes found in: .note
>   Owner                Data size 	Description
>   Linux                0x00000004	Unknown note type: (0x00000000)
>    description data: 06 00 00 00
> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x20
> readelf: Warning:  type: 0x78, namesize: 0x00000100, descsize: 0x756e694c, alignment: 8
> [hjl@...-skx-1 vdso]$
> 
> Since note.gnu.property section in vDSO is not checked by dynamic linker,
> this patch discards .note.gnu.property sections in vDSO by adding

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette