On Thu, Jan 07, 2021 at 05:29:06PM +0000, Vincenzo Frascino wrote:
> MTE provides an asynchronous mode for detecting tag exceptions. In
> particular instead of triggering a fault the arm64 core updates a
> register which is checked by the kernel at the first entry after the tag
> exception has occurred.
Just rephrase the "tag exception" here as there's no exception taken.
Also we don't check this only when the kernel is first entered after a
tag check fault, as per patch 3.
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -153,8 +153,35 @@ void mte_init_tags(u64 max_tag)
>
> void mte_enable_kernel(enum kasan_arg_mode mode)
> {
> - /* Enable MTE Sync Mode for EL1. */
> - sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> + const char *m;
> +
> + /* Preset parameter values based on the mode. */
> + switch (mode) {
> + case KASAN_ARG_MODE_OFF:
> + return;
> + case KASAN_ARG_MODE_LIGHT:
> + /* Enable MTE Async Mode for EL1. */
> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK,
> SCTLR_ELx_TCF_ASYNC);
> + m = "asynchronous";
> + break;
> + case KASAN_ARG_MODE_DEFAULT:
> + case KASAN_ARG_MODE_PROD:
> + case KASAN_ARG_MODE_FULL:
> + /* Enable MTE Sync Mode for EL1. */
> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK,
> SCTLR_ELx_TCF_SYNC);
> + m = "synchronous";
> + break;
> + default:
> + /*
> + * kasan mode should be always set hence we should
> + * not reach this condition.
> + */
> + WARN_ON_ONCE(1);
> + return;
> + }
I guess the switch statement here will be re-written as we want kasan to
drive the actual sync/async modes as it sees fit rather than MTE
guessing what PROD/FULL/LIGHT means.
--
Catalin
