On Thu, Aug 15, 2019 at 5:44 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>
> First rename the sysctl control to abi.tagged_addr_disabled and make it
> default off (zero). When abi.tagged_addr_disabled == 1, only block the
> enabling of the TBI ABI via prctl(PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE).
> Getting the status of the ABI or disabling it is still allowed.
>
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Acked-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
> arch/arm64/kernel/process.c | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 76b7c55026aa..03689c0beb34 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -579,17 +579,22 @@ void arch_setup_new_exec(void)
> /*
> * Control the relaxed ABI allowing tagged user addresses into the kernel.
> */
> -static unsigned int tagged_addr_prctl_allowed = 1;
> +static unsigned int tagged_addr_disabled;
>
> long set_tagged_addr_ctrl(unsigned long arg)
> {
> - if (!tagged_addr_prctl_allowed)
> - return -EINVAL;
> if (is_compat_task())
> return -EINVAL;
> if (arg & ~PR_TAGGED_ADDR_ENABLE)
> return -EINVAL;
>
> + /*
> + * Do not allow the enabling of the tagged address ABI if globally
> + * disabled via sysctl abi.tagged_addr_disabled.
> + */
> + if (arg & PR_TAGGED_ADDR_ENABLE && tagged_addr_disabled)
> + return -EINVAL;
> +
> update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);
>
> return 0;
> @@ -597,8 +602,6 @@ long set_tagged_addr_ctrl(unsigned long arg)
>
> long get_tagged_addr_ctrl(void)
> {
> - if (!tagged_addr_prctl_allowed)
> - return -EINVAL;
> if (is_compat_task())
> return -EINVAL;
>
> @@ -618,9 +621,9 @@ static int one = 1;
>
> static struct ctl_table tagged_addr_sysctl_table[] = {
> {
> - .procname = "tagged_addr",
> + .procname = "tagged_addr_disabled",
> .mode = 0644,
> - .data = &tagged_addr_prctl_allowed,
> + .data = &tagged_addr_disabled,
> .maxlen = sizeof(int),
> .proc_handler = proc_dointvec_minmax,
> .extra1 = &zero,
