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

[Yu-cheng Yu]

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