[PATCH] powerpc/kernel: Fix potential spectre v1 in syscall

[Breno Leitao]

On Tue, Mar 12, 2024 at 10:07:54PM +1100, Michael Ellerman wrote:
> Breno Leitao <leitao at debian.org> writes:
> > On Tue, Mar 12, 2024 at 08:17:42AM +0000, Christophe Leroy wrote:
> >> +Nathan as this is RTAS related.
> >> 
> >> Le 21/08/2018 à 20:42, Breno Leitao a écrit :
> >> > The rtas syscall reads a value from a user-provided structure and uses it
> >> > to index an array, being a possible area for a potential spectre v1 attack.
> >> > This is the code that exposes this problem.
> >> > 
> >> > 	args.rets = &args.args[nargs];
> >> > 
> >> > The nargs is an user provided value, and the below code is an example where
> >> > the 'nargs' value would be set to XX.
> >> > 
> >> > 	struct rtas_args ra;
> >> > 	ra.nargs = htobe32(XX);
> >> > 	syscall(__NR_rtas, &ra);
> >> 
> >> 
> >> This patch has been hanging around in patchwork since 2018 and doesn't 
> >> apply anymore. Is it still relevant ? If so, can you rebase et resubmit ?
> >
> > This seems to be important, since nargs is a user-provided value. I can
> > submit it if the maintainers are willing to accept. I do not want to
> > spend my time if no one is willing to review it.
> 
> My memory is that I didn't think it was actually a problem, because all
> we do is memset args.rets to zero. I thought I'd talked to you on Slack
> about it, but maybe I didn't.
> 
> Anyway we should probably just fix it to be safe and keep the static
> checkers happy.
> 
> I'll rebase it and apply it, I'm sure you've got better things to do :)

Awesome. Thanks Michael!