[PATCH v5] ARM: Implement SLS mitigation

[Linus Walleij]

On Fri, Mar 5, 2021 at 12:23 AM Jian Cai <jiancai at google.com> wrote:
> On Wed, Mar 3, 2021 at 7:04 AM Linus Walleij <linus.walleij at linaro.org> wrote:
> >
> > On Tue, Feb 23, 2021 at 3:36 AM Jian Cai <jiancai at google.com> wrote:
> >
> > > This patch adds CONFIG_HARDEN_SLS_ALL that can be used to turn on
> > > -mharden-sls=all, which mitigates the straight-line speculation
> > > vulnerability, speculative execution of the instruction following some
> > > unconditional jumps. Notice -mharden-sls= has other options as below,
> > > and this config turns on the strongest option.
> > >
> > > all: enable all mitigations against Straight Line Speculation that are implemented.
> > > none: disable all mitigations against Straight Line Speculation.
> > > retbr: enable the mitigation against Straight Line Speculation for RET and BR instructions.
> > > blr: enable the mitigation against Straight Line Speculation for BLR instructions.
> >
> > I heard about compiler protection for this, so nice to see it happening!
> >
> > Would you happen to know if there is any plan to do the same for GCC?
> > I know you folks at Google like LLVM, but if you know let us know.
>
> I think gcc also has these options.
> https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html

And how does that work with this part of your patch:

+#define SLS_TEXT                                       \
+       ALIGN_FUNCTION();                              \
+       *(.text.__llvm_slsblr_thunk_*)

This does not look compiler agnostic?

Yours,
Linus Walleij