Introduce new flag -- MTE_CTRL_STORE_ONLY used to set store-only tag check.
This flag isn't overrided by prefered tcf flag setting but set together
with prefered setting of way to report tag check fault.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 arch/arm64/include/asm/processor.h |  2 ++
 arch/arm64/kernel/mte.c            | 11 ++++++++++-
 arch/arm64/kernel/process.c        |  6 +++++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 1bf1a3b16e88..61d62bfd5a7b 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -23,6 +23,8 @@
 #define MTE_CTRL_TCF_ASYNC		(1UL << 17)
 #define MTE_CTRL_TCF_ASYMM		(1UL << 18)
 
+#define MTE_CTRL_STORE_ONLY		(1UL << 19)
+
 #ifndef __ASSEMBLY__
 
 #include <linux/build_bug.h>
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 2fbfd27ff5f2..e5e773844889 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -200,7 +200,7 @@ static void mte_update_sctlr_user(struct task_struct *task)
 	 * program requested values go with what was requested.
 	 */
 	resolved_mte_tcf = (mte_ctrl & pref) ? pref : mte_ctrl;
-	sctlr &= ~SCTLR_EL1_TCF0_MASK;
+	sctlr &= ~(SCTLR_EL1_TCF0_MASK | SCTLR_EL1_TCSO0_MASK);
 	/*
 	 * Pick an actual setting. The order in which we check for
 	 * set bits and map into register values determines our
@@ -212,6 +212,10 @@ static void mte_update_sctlr_user(struct task_struct *task)
 		sctlr |= SYS_FIELD_PREP_ENUM(SCTLR_EL1, TCF0, ASYNC);
 	else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC)
 		sctlr |= SYS_FIELD_PREP_ENUM(SCTLR_EL1, TCF0, SYNC);
+
+	if (mte_ctrl & MTE_CTRL_STORE_ONLY)
+		sctlr |= SYS_FIELD_PREP(SCTLR_EL1, TCSO0, 1);
+
 	task->thread.sctlr_user = sctlr;
 }
 
@@ -371,6 +375,9 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 	    (arg & PR_MTE_TCF_SYNC))
 		mte_ctrl |= MTE_CTRL_TCF_ASYMM;
 
+	if (arg & PR_MTE_STORE_ONLY)
+		mte_ctrl |= MTE_CTRL_STORE_ONLY;
+
 	task->thread.mte_ctrl = mte_ctrl;
 	if (task == current) {
 		preempt_disable();
@@ -398,6 +405,8 @@ long get_mte_ctrl(struct task_struct *task)
 		ret |= PR_MTE_TCF_ASYNC;
 	if (mte_ctrl & MTE_CTRL_TCF_SYNC)
 		ret |= PR_MTE_TCF_SYNC;
+	if (mte_ctrl & MTE_CTRL_STORE_ONLY)
+		ret |= PR_MTE_STORE_ONLY;
 
 	return ret;
 }
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 42faebb7b712..cea4a23a15de 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -815,10 +815,14 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
 	if (is_compat_thread(ti))
 		return -EINVAL;
 
-	if (system_supports_mte())
+	if (system_supports_mte()) {
 		valid_mask |= PR_MTE_TCF_SYNC | PR_MTE_TCF_ASYNC \
 			| PR_MTE_TAG_MASK;
 
+		if (cpus_have_cap(ARM64_MTE_STORE_ONLY))
+			valid_mask |= PR_MTE_STORE_ONLY;
+	}
+
 	if (arg & ~valid_mask)
 		return -EINVAL;
 
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}

On Thu, Apr 10, 2025 at 09:07:22AM +0100, Yeoreum Yun wrote:
> Introduce new flag -- MTE_CTRL_STORE_ONLY used to set store-only tag check.
> This flag isn't overrided by prefered tcf flag setting but set together

Nit: s/overrided/overridden/

> with prefered setting of way to report tag check fault.

The preferred mode set via sysfs is about whether we want synchronous or
asynchronous tag check faults for reads/writes (or asymmetric). The
store-only checking can be combined with sync/async, so they are
slightly complementary. The question is whether one wants some global
knob to turn on store-only in combination with sync/async. We could add
more strings for sysfs like "(a)sync+storeonly"

It would be good to hear Peter's opinion from an Android perspective.

-- 
Catalin

Hi Catalin,

> On Thu, Apr 10, 2025 at 09:07:22AM +0100, Yeoreum Yun wrote:
> > Introduce new flag -- MTE_CTRL_STORE_ONLY used to set store-only tag check.
> > This flag isn't overrided by prefered tcf flag setting but set together
>
> Nit: s/overrided/overridden/

Thanks!

>
> > with prefered setting of way to report tag check fault.
>
> The preferred mode set via sysfs is about whether we want synchronous or
> asynchronous tag check faults for reads/writes (or asymmetric). The
> store-only checking can be combined with sync/async, so they are
> slightly complementary. The question is whether one wants some global
> knob to turn on store-only in combination with sync/async. We could add
> more strings for sysfs like "(a)sync+storeonly"
>
> It would be good to hear Peter's opinion from an Android perspective.

Thanks to add, I'll wait for his comment for this :)

> --
> Catalin

--
Sincerely,
Yeoreum Yun