On Thu, Jan 7, 2021 at 6:25 PM Vincenzo Frascino <vincenzo.frasc...@arm.com> wrote: > > Hi Andrey, > > On 1/7/21 4:29 PM, Andrey Konovalov wrote: > > On Wed, Jan 6, 2021 at 12:56 PM Vincenzo Frascino > > <vincenzo.frasc...@arm.com> 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. > >> > >> Add support for MTE asynchronous mode. > >> > >> The exception handling mechanism will be added with a future patch. > >> > >> Note: KASAN HW activates async mode via kasan.mode kernel parameter. > >> The default mode is set to synchronous. > >> > >> Cc: Catalin Marinas <catalin.mari...@arm.com> > >> Cc: Will Deacon <will.dea...@arm.com> > >> Signed-off-by: Vincenzo Frascino <vincenzo.frasc...@arm.com> > >> --- > >> arch/arm64/kernel/mte.c | 31 +++++++++++++++++++++++++++++-- > >> 1 file changed, 29 insertions(+), 2 deletions(-) > >> > >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > >> index 24a273d47df1..5d992e16b420 100644 > >> --- 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; > >> + } > >> + > >> + pr_info_once("MTE: enabled in %s mode at EL1\n", m); > >> + > >> isb(); > >> } > >> > >> -- > >> 2.29.2 > >> > > > > Hi Vincenzo, > > > > It would be cleaner to pass a bool to mte_enable_kernel() and have it > > indicate sync/async mode. This way you don't have to pull all these > > KASAN constants into the arm64 code. > > > > Boolean arguments are generally bad for legibility, hence I tend to avoid > them. > In this case exposing the constants does not seem a big issue especially > because > the only user of this code is "KASAN_HW_TAGS" and definitely improves its > legibility hence I would prefer to keep it as is.
I don't like that this spills KASAN internals to the arm64 code. Let's add another enum with two values and pass it as an argument then. Something like: enum mte_mode { ARM_MTE_SYNC, ARM_MTE_ASYNC }