Re: [PATCH v8 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file

Dave Martin
2019-08-20T10:02:10Z

On Tue, Aug 13, 2019 at 01:52:20PM -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 specific
> arch_parse_property() and 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);
> ...
> }
>
> This patch is derived from code provided by H.J. Lu <hjl.tools@gmail.com>.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

[...]

For the hell of it, I tried implementing an alternate version [1] that
tries to integrate into the existing ELF loader more directly.

This may or may not be a better approach, but tries to solve some
issues such as not repeatedly reading and parsing the properties.

Cheers
---Dave

[1] [RFC PATCH 0/2] ELF: Alternate program property parser