Re: [PATCH v2] powerpc/uprobes: Validation for prefixed instruction

[Ravi Bangoria]

On 2/4/21 6:45 PM, Naveen N. Rao wrote:
> On 2021/02/04 04:19PM, Ravi Bangoria wrote:
> > On 2/4/21 4:17 PM, Ravi Bangoria wrote:
> > > Don't allow Uprobe on 2nd word of a prefixed instruction. As per
> > > ISA 3.1, prefixed instruction should not cross 64-byte boundary.
> > > So don't allow Uprobe on such prefixed instruction as well.
> > >
> > > There are two ways probed instruction is changed in mapped pages.
> > > First, when Uprobe is activated, it searches for all the relevant
> > > pages and replace instruction in them. In this case, if we notice
> > > that probe is on the 2nd word of prefixed instruction, error out
> > > directly. Second, when Uprobe is already active and user maps a
> > > relevant page via mmap(), instruction is replaced via mmap() code
> > > path. But because Uprobe is invalid, entire mmap() operation can
> > > not be stopped. In this case just print an error and continue.
> >
> > @mpe,
> >
> > arch_uprobe_analyze_insn() can return early if
> > cpu_has_feature(CPU_FTR_ARCH_31) is not set. But that will
> > miss out a rare scenario of user running binary with prefixed
> > instruction on p10 predecessors. Please let me know if I
> > should add cpu_has_feature(CPU_FTR_ARCH_31) or not.
>
> The check you are adding is very specific to prefixed instructions, so
> it makes sense to add a cpu feature check for v3.1.
>
> On older processors, those are invalid instructions like any other. The
> instruction emulation infrastructure will refuse to emulate it and the
> instruction will be single stepped.

Sure will add it.

Ravi