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Date:   Tue, 27 Apr 2021 15:58:23 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Bill Wendling <morbo@google.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO
Message-ID: <202104271557.412DD365A@keescook>
References: <20210423205159.830854-1-morbo@google.com>
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On Fri, Apr 23, 2021 at 01:51:59PM -0700, Bill Wendling wrote:
> The arm64 assembler 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 the kernel 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 */
>   }
> 
> The NOTE segment generated by the vDSO linker script is aligned to 4 bytes.
> But the .note.gnu.property section must be aligned to 8 bytes on arm64.
> 
>   $ 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
> 
> Since the note.gnu.property section in the vDSO is not checked by the
> dynamic linker, discard the .note.gnu.property sections in the vDSO.
> 
> Similar to commit 4caffe6a28d31 ("x86/vdso: Discard .note.gnu.property
> sections in vDSO"), but for arm64.
> 
> Signed-off-by: Bill Wendling <morbo@google.com>

Seems good to me. If we ever need the BTI markings, etc, for the vDSO,
we can revisit it then.

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

-- 
Kees Cook