Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file

Yu-cheng Yu
2019-06-10T16:37:13Z

On Fri, 2019-06-07 at 19:01 +0100, Dave Martin wrote:
> On Thu, Jun 06, 2019 at 01:06:41PM -0700, Yu-cheng Yu wrote:
> > An ELF file's .note.gnu.property indicates features the executable file
> > can support. For example, the property GNU_PROPERTY_X86_FEATURE_1_AND
> > indicates the file supports GNU_PROPERTY_X86_FEATURE_1_IBT and/or
> > GNU_PROPERTY_X86_FEATURE_1_SHSTK.
> >
> > With this patch, if an arch needs to setup features from ELF properties,
> > it needs CONFIG_ARCH_USE_GNU_PROPERTY to be set, and a specific
> > arch_setup_property().
> >
> > For example, for X86_64:
> >
> > int arch_setup_property(void *ehdr, void *phdr, struct file *f, bool inter)
> > {
> > int r;
> > uint32_t property;
> >
> > r = get_gnu_property(ehdr, phdr, f, GNU_PROPERTY_X86_FEATURE_1_AND,
> > &property);
> > ...
> > }
>
> Although this code works for the simple case, I have some concerns about
> some aspects of the implementation here. There appear to be some bounds
> checking / buffer overrun issues, and the code seems quite complex.
>
> Maybe this patch tries too hard to be compatible with toolchains that do
> silly things such as embedding huge notes in an executable, or mixing
> NT_GNU_PROPERTY_TYPE_0 in a single PT_NOTE with a load of junk not
> relevant to the loader. I wonder whether Linux can dictate what
> interpretation(s) of the ELF specs it is prepared to support, rather than
> trying to support absolutely anything.

To me, looking at PT_GNU_PROPERTY and not trying to support anything is a
logical choice. And it breaks only a limited set of toolchains.

I will simplify the parser and leave this patch as-is for anyone who wants to
back-port. Are there any objections or concerns?

Yu-cheng