Re: [PATCH] kernel/sys.c: fix possible spectre-v1 in do_prlimit()

[Cyrill Gorcunov]

On Tue, May 28, 2019 at 10:37:10AM +0800, Dianzhang Chen wrote:
> Hi,
> Because when i reply your emailïi always get 'Message rejected' from
> gmail(get this rejection from all the recipients). I still don't know
> how to deal with it, so i reply your email here:

Hi! This is weird. Next time simply reply to LKML (I CC'ed it back).

> Because of speculative execution, the attacker can bypass the bound
> check `if (resource >= RLIM_NLIMITS)`.

And then misprediction get detected and execution is dropped. So I
still don't see a problem here, since we don't leak info even in
such case.

That said I don't mind for this patch but rather in a sake of
code clarity, not because of spectre issue since it has
nothing to do here.

> as for array_index_nospec(index, size), it will clamp the index within
> the range of [0, size), and attacker can't exploit speculative
> execution to make the index out of range [0, size).
> 
> 
> For more detail, please check the link below:
> 
> https://github.com/torvalds/linux/commit/f3804203306e098dae9ca51540fcd5eb700d7f40