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SubjectRe: [PATCH] x86/speculation: Check whether speculation is force disabled
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On 6/3/20 3:12 AM, Tada, Kenta (Sony) wrote:
> Once PR_SPEC_FORCE_DISABLE is set, users cannot set PR_SPEC_ENABLE.
> This commit checks whether PR_SPEC_FORCE_DISABLE was previously set.
>
> Signed-off-by: Kenta Tada <Kenta.Tada@sony.com>
> ---
> arch/x86/kernel/cpu/bugs.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index ed54b3b21c39..678ace157035 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1173,6 +1173,9 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
> if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
> spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
> return -EPERM;
> + /* If speculation is force disabled, enable is not allowed */
> + if (task_spec_ib_force_disable(task))
> + return -EPERM;
> task_clear_spec_ib_disable(task);
> task_update_spec_tif(task);
> break;

There is a comment up a few lines about this:

                /*
                 * Indirect branch speculation is always allowed when
                 * mitigation is force disabled.
                 */
It conflicts with your new code. We can have an argument on whether IB
should follow how SSB is being handled. Before that is settled,

Nacked-by: Waiman Long <longman@redhat.com>

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