Re: [PATCH 13/18] arm64: preserve x18 when CPU is suspended

Nick Desaulniers
2019-10-18T16:49:53Z

On Fri, Oct 18, 2019 at 9:11 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> Don't lose the current task's shadow stack when the CPU is suspended.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
> arch/arm64/mm/proc.S | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index fdabf40a83c8..9a8bd4bc8549 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -73,6 +73,9 @@ alternative_endif
> stp x8, x9, [x0, #48]
> stp x10, x11, [x0, #64]
> stp x12, x13, [x0, #80]
> +#ifdef CONFIG_SHADOW_CALL_STACK
> + stp x18, xzr, [x0, #96]

Could this be a str/ldr of just x18 rather than stp/ldp of x18 +
garbage? Maybe there's no real cost difference, or some kind of
alignment invariant?

> +#endif
> ret
> ENDPROC(cpu_do_suspend)
>
> @@ -89,6 +92,9 @@ ENTRY(cpu_do_resume)
> ldp x9, x10, [x0, #48]
> ldp x11, x12, [x0, #64]
> ldp x13, x14, [x0, #80]
> +#ifdef CONFIG_SHADOW_CALL_STACK
> + ldp x18, x19, [x0, #96]
> +#endif
> msr tpidr_el0, x2
> msr tpidrro_el0, x3
> msr contextidr_el1, x4
> --
> 2.23.0.866.gb869b98d4c-goog
>

--
Thanks,
~Nick Desaulniers