Re: RFC: GCC plugin to find encrypted function pointer calls in glibc

[Carlos O'Donell <carlos at redhat dot com>]

On 04/29/2016 06:23 AM, Aldy Hernandez wrote:
> Since I would prefer not to assume the output of all inline asm's are
> a demangling operation, I would like to get feedback from the
> community on what would be preferred.

Awesome looking work!
 
> My preferred approach is to add an attribute to an inline function that would wrap the asm:
> 
>     __attribute__((decrypt)) static inline funcp demangler (funcp f)
>     {
>         asm("blah");
>     }
> 
> This is straightforward, clean, and follows language semantics (not
> to mention that I already have it implemented into my plugin :)), but
> Florian made funny faces when I showed it to him, so here I am :).

You can build glibc with gcc 4.7 or newer.

(1) static inline wrapper with function attribute:

For a representative set of architectures, say x86_64, i686, ppc64,
s390x, aarch64, and arm, does a 4.7 or newer compiler do as good a
job with a static inline function as it does with the macro that
evaluates to a bare assembly?

(2) Asm attribute:

We have function, variable, type, label, and enumerator attributes,
why not support them on asm statements to mark them as decrypt or
encrypt functions? This would lend itself to a more natural conversion
of inline assembly that users may want to write and embed into their
programs.

It is entirely conceivable that (1) does a good-enough job, and we
add (2) at the same time to the latest gcc and backport. When we raise
the supported build compiler version we can switch to (2) if needed.

-- 
Cheers,
Carlos.