Re: [PATCH 01/14] x86/cfi: Wreck things...

[Josh Poimboeuf]

On Fri, Sep 27, 2024 at 09:48:57PM +0200, Peter Zijlstra wrote:
> vmlinux.o: warning: objtool: .export_symbol+0x3c9f0: data relocation to !ENDBR: entry_untrain_ret+0x0
> 
> Which states that while these functions are exported and (directly)
> callable, they cannot be called indirectly. There are two solutions:

IIRC, exported symbols are by far the most common "need" for ENDBR.  But
presumably the vast majority of them aren't being indirect called.

>  - exclude the .export_symbol section from validation; effectively
>    saying that having linkable but not indirectly callable exports are
>    fine by default, or

This is confusingly inconsistent IMO.

>  - make all of those use SYM_TYPED_FUNC_START to restore the
>    traditional (and expected, but less secure?) behaviour.

Why not just make SYM_FUNC_START imply "typed"?  That's consistent with
what the compiler does anyway right?

Even better, require exported+indirect-called symbols to use
EXPORT_SYMBOL_TYPED, otherwise they get sealed.  I suppose we'd need to
add some module-to-vmlinux ENDBR validation to make sure modules don't
get broken by this.

-- 
Josh