[PATCH v3 3/3] arm64: kprobe: disable probe of fault prone ptrauth instruction

[Mark Rutland]

On Mon, Jun 22, 2020 at 03:40:26PM +0100, Dave Martin wrote:
> On Thu, Jun 18, 2020 at 10:40:29AM +0530, Amit Daniel Kachhap wrote:
> > This patch disables the probing of authenticate ptrauth instruction (AUT*)
> > which falls under the hint instructions region. This is done to disallow
> > probe of authenticate instruction which may lead to ptrauth faults with the
> > addition of Armv8.6 enhanced ptrauth features.

> > diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
> > index 263d5fba4c8a..c26c638b260e 100644
> > --- a/arch/arm64/kernel/probes/decode-insn.c
> > +++ b/arch/arm64/kernel/probes/decode-insn.c
> > @@ -42,7 +42,7 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
> >  			     != AARCH64_INSN_SPCLREG_DAIF;
> >  
> >  		/*
> > -		 * The HINT instruction is is problematic when single-stepping,
> > +		 * The HINT instruction is problematic when single-stepping,
> 
> Nit: doesn't matter too much, but ideally this should be a separate
> patch (or just don't bother).

Agreed. I also think if we change this at all we should drop the comment
entirely: it's somewhat misleading given it implies NOP is the only HINT
space instruction that can be sfely stepped, and doesn't suggest *why*
hints might be proboematic.

Thanks,
Mark.