Re: [PATCH 05/15] x86: Implement function_nocfi

[Andy Lutomirski]

On Sun, Apr 18, 2021 at 9:17 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> On Sat, Apr 17 2021 at 17:11, Andy Lutomirski wrote:
> > On Sat, Apr 17, 2021 at 4:53 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> >> which works for
> >>
> >>       foo = function_nocfi(bar);
> >
> > I agree in general.  But right now, we have, in asm/proto.h:
> >
> > void entry_SYSCALL_64(void);
> >
> > and that's pure nonsense.  Depending on your point of view,
> > entry_SYSCALL_64 is a symbol that resolves to an integer or it's an
> > array of bytes containing instructions, but it is most definitely not
> > a function void (void).  So, regardless of any CFI stuff, I propose
> > that we standardize our handling of prototypes of symbols that are
> > opaque to the C compiler.  Here are a couple of choices:
> >
> > Easy one:
> >
> > extern u8 entry_SYSCALL_64[];
> >
> > Slightly more complicated:
> >
> > struct opaque_symbol;
> > extern struct opaque_symbol entry_SYSCALL_64;
> >
> > The opaque_symbol variant avoids any possible confusion over the weird
> > status of arrays in C, and it's hard to misuse, since struct
> > opaque_symbol is an incomplete type.
>
> Makes sense.

Sami, do you want to do this as part of your series or should I write a patch?