[PATCH 0/2] arm64: gcs: Return -EPERM when changes are prevented by locking

[PATCH 0/2] arm64: gcs: Return -EPERM when changes are prevented by locking

[Mark Brown]

When we refuse to change the GCS configuraiton due to locking we
currently return -EBUSY which is an odd choice.  The only userspace I
found that relies on this value at present is the kselftest and other
architectures are using the more obvious -EPERM here let's switch.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
Mark Brown (2):
      arm64: gcs: Return -EPERM not -EBUSY for prctl() locking failures
      kselftest/arm64: Check for -EPERM not -EBUSY in the locking test

 arch/arm64/include/asm/gcs.h                    | 2 +-
 tools/testing/selftests/arm64/gcs/gcs-locking.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)
---
base-commit: df2908090cda368b01ff43709f51890076c56157
change-id: 20260910-arm64-gcs-lock-eperm-06ce8f8e5250

Best regards,
--  
Mark Brown <broonie@kernel.org>

[PATCH 1/2] arm64: gcs: Return -EPERM not -EBUSY for prctl() locking failures

[Mark Brown]

When we refuse to perform a GCS configuration change due to locking we
currently return -EBUSY which is an odd error code to return.  While the
selftest does currently check for this it is unlikely that we have any
practical users relying on the behaviour at this point so let's change
to return the more descriptive -EPERM instead like other architectures.

Reported-by: Bill Roberts <bill.roberts@foss.arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/gcs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index 8fa0707069e8..bbc22e382cfe 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h
@@ -76,7 +76,7 @@ static inline int gcs_check_locked(struct task_struct *task,
 	new_val &= task->thread.gcs_el0_locked;
 
 	if (cur_val != new_val)
-		return -EBUSY;
+		return -EPERM;
 
 	return 0;
 }

-- 
2.47.3

[PATCH 2/2] kselftest/arm64: Check for -EPERM not -EBUSY in the locking test

[Mark Brown]

The API has been updated to return the more permissive -EPERM rather
than -EBUSY, update the selftest to reflect this.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/arm64/gcs/gcs-locking.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/arm64/gcs/gcs-locking.c b/tools/testing/selftests/arm64/gcs/gcs-locking.c
index 1e6abb136ffd..f780f0c7b8dd 100644
--- a/tools/testing/selftests/arm64/gcs/gcs-locking.c
+++ b/tools/testing/selftests/arm64/gcs/gcs-locking.c
@@ -115,7 +115,7 @@ TEST_F(valid_modes, enable_lock_disable)
 	ASSERT_EQ(ret, 0);
 
 	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0);
-	ASSERT_EQ(ret, -EBUSY);
+	ASSERT_EQ(ret, -EPERM);
 
 	_exit(0);
 }
@@ -131,7 +131,7 @@ TEST_F(valid_modes, lock_enable)
 
 	ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
 			  variant->mode);
-	ASSERT_EQ(ret, -EBUSY);
+	ASSERT_EQ(ret, -EPERM);
 
 	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &mode, 0, 0, 0);
 	ASSERT_EQ(ret, 0);

-- 
2.47.3