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Date:   Thu, 30 Jan 2020 12:08:07 -0800
From:   Kees Cook <keescook@chromium.org>
To:     "H.J. Lu" <hjl.tools@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Thomas Lendacky <Thomas.Lendacky@amd.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: Re: [PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux
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On Thu, Jan 30, 2020 at 12:04:54PM -0800, H.J. Lu wrote:
> > I don't understand this. "may not be incompatible"? Is there an error
> > generated? If so, what does it look like?
> 
> When -mx86-used-note=yes is passed to assembler, with my patch, I got
> 
> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
> 
> Displaying notes found in: .notes
>   Owner                Data size Description
>   Xen                  0x00000006 Unknown note type: (0x00000006)
>    description data: 6c 69 6e 75 78 00
>   Xen                  0x00000004 Unknown note type: (0x00000007)
>    description data: 32 2e 36 00
>   Xen                  0x00000008 Unknown note type: (0x00000005)
>    description data: 78 65 6e 2d 33 2e 30 00
>   Xen                  0x00000008 Unknown note type: (0x00000003)
>    description data: 00 00 00 80 ff ff ff ff
>   Xen                  0x00000008 Unknown note type: (0x0000000f)
>    description data: 00 00 00 00 80 00 00 00
>   Xen                  0x00000008 NT_VERSION (version)
>    description data: 80 a1 ba 82 ff ff ff ff
>   Xen                  0x00000008 NT_ARCH (architecture)
>    description data: 00 10 00 81 ff ff ff ff
>   Xen                  0x00000029 Unknown note type: (0x0000000a)
>    description data: 21 77 72 69 74 61 62 6c 65 5f 70 61 67 65 5f 74
> 61 62 6c 65 73 7c 70 61 65 5f 70 67 64 69 72 5f 61 62 6f 76 65 5f 34
> 67 62
>   Xen                  0x00000004 Unknown note type: (0x00000011)
>    description data: 01 88 00 00
>   Xen                  0x00000004 Unknown note type: (0x00000009)
>    description data: 79 65 73 00
>   Xen                  0x00000008 Unknown note type: (0x00000008)
>    description data: 67 65 6e 65 72 69 63 00
>   Xen                  0x00000010 Unknown note type: (0x0000000d)
>    description data: 01 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00
>   Xen                  0x00000004 Unknown note type: (0x0000000e)
>    description data: 01 00 00 00
>   Xen                  0x00000004 Unknown note type: (0x00000010)
>    description data: 01 00 00 00
>   Xen                  0x00000008 Unknown note type: (0x0000000c)
>    description data: 00 00 00 00 00 80 ff ff
>   Xen                  0x00000008 Unknown note type: (0x00000004)
>    description data: 00 00 00 00 00 00 00 00
>   GNU                  0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
>     Build ID: 11c73de2922f593e1b35b92ab3c70eaa1a80fa83
>   Linux                0x00000018 OPEN
>    description data: 35 2e 33 2e 39 2d 32 30 30 2e 30 2e 66 63 33 30
> 2e 78 38 36 5f 36 34 00
>   Xen                  0x00000008 Unknown note type: (0x00000012)
>    description data: 70 04 00 01 00 00 00 00
> [hjl@gnu-skx-1 linux]$
> 
> Without my patch,
> 
> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
> 
> Displaying notes found in: .notes
>   Owner                Data size Description
>   Xen                  0x00000006 Unknown note type: (0x00000006)
>    description data: 6c 69 6e 75 78 00
>   Xen                  0x00000004 Unknown note type: (0x00000007)
>    description data: 32 2e 36 00
>   xen-3.0              0x00000005 Unknown note type: (0x006e6558)
>    description data: 08 00 00 00 03
> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
> readelf: Warning:  type: 0xffffffff, namesize: 0x006e6558, descsize:
> 0x80000000, alignment: 8
> [hjl@gnu-skx-1 linux]$

What is the source of this failure? Does readelf need updating instead?
Is the linking step producing an invalid section? It seems like
discarding the properties isn't the right solution here?

-- 
Kees Cook