RE: [PATCH v4] ARM: Implement SLS mitigation

[David Laight]

From: Linus Walleij
> Sent: 03 March 2021 15:19
> 
> On Tue, Feb 23, 2021 at 11:05 AM Will Deacon <will@xxxxxxxxxx> wrote:
> > On Mon, Feb 22, 2021 at 01:50:06PM -0800, Jian Cai wrote:
> > > I am not sure if there are any plans to protect assembly code and I
> > > will leave it to the Arm folks since they know a whole lot better. But
> > > even without that part, we should still have better protection,
> > > especially when overhead does not look too bad: I did some preliminary
> > > experiments on ChromeOS, code size of vmlinux increased 3%, and there
> > > were no noticeable changes to run-time performance of the benchmarks I
> > > used.
> >
> > If the mitigation is required, I'm not sure I see a lot of point in only
> > doing a half-baked job of it. It feels a bit like a box-ticking exercise,
> > in which case any overhead is too much.
> 
> I wrote some suggestions on follow-ups in my reply, and I can
> help out doing some of the patches, I think.
> 
> Since ARM32 RET is mov pc, <>
> git grep 'mov.*pc,' | wc -l gives 93 sites in arch/arm.
> I suppose these need to come out:
> 
> mov pc, lr
> dsb(nsh);
> isb();

Won't that go horribly wrong for conditional returns?

	David

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