Re: [PATCH v10 00/13] arm64: Branch Target Identification support

[Mark Rutland]

On Mon, Mar 23, 2020 at 02:39:55PM +0000, Catalin Marinas wrote:
> On Mon, Mar 23, 2020 at 01:57:22PM +0000, Mark Rutland wrote:
> > On Mon, Mar 23, 2020 at 01:24:12PM +0000, Mark Brown wrote:
> > > On Mon, Mar 23, 2020 at 12:21:44PM +0000, Catalin Marinas wrote:
> > > > On Fri, Mar 20, 2020 at 05:39:46PM +0000, Szabolcs Nagy wrote:
> > > 
> > > > +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
> > > > +                        bool has_interp, bool is_interp)
> > > > +{
> > > > +       if (is_interp != has_interp)
> > > > +               return prot;
> > > > +
> > > > +       if (!(state->flags & ARM64_ELF_BTI))
> > > > +               return prot;
> > > > +
> > > > +       if (prot & PROT_EXEC)
> > > > +               prot |= PROT_BTI;
> > > > +
> > > > +       return prot;
> > > > +}

> > I think it would be best to document the current behaviour, as it's a
> > simple ABI that we can guarantee, and the dynamic linker will have to be
> > aware of BTI in order to do the right thing anyhow.
> 
> That's a valid point. If we have an old dynamic linker and the kernel
> enabled BTI automatically for the main executable, could things go wrong
> (e.g. does the PLT need to be BTI-aware)?

Also worth noting that an old dynamic linker won't have ARM64_ELF_BTI
set, so the kernel will not enable BTI for this.

Mark.