[PATCH 2/2] kselftest/arm64: Add test for atomic futex uaccess with POE

[Kevin Brodsky <kevin.brodsky@arm.com>]

Add a new test to ensure that atomic futex uaccess succeeds on
memory mapped with a non-default POIndex/pkey.

In the absence of FEAT_LSUI, atomic futex uaccess operations such as
those triggered by FUTEX_WAKE_OP use privileged atomic load/store
instructions and thus cannot have user permission overlays applied
(as per POR_EL0). In case the kernel enabled POE at EL1, it is worth
checking that PIR_EL1 isn't mistakenly configured to have kernel
overlays (POR_EL1) applied instead, as that would fail for non-zero
pkeys.

Note that if such misconfiguration occurs, futex_wake_op() may get
stuck in an infinite loop because futex_atomic_op_inuser() will fail
but fault_in_user_writeable() will still report success.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 tools/testing/selftests/arm64/Makefile        |  2 +-
 tools/testing/selftests/arm64/poe/.gitignore  |  2 +
 tools/testing/selftests/arm64/poe/Makefile    |  6 +++
 tools/testing/selftests/arm64/poe/poe_futex.c | 62 +++++++++++++++++++++++++++
 4 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/arm64/Makefile b/tools/testing/selftests/arm64/Makefile
index e456f3b62fa1..bad5c3b33dce 100644
--- a/tools/testing/selftests/arm64/Makefile
+++ b/tools/testing/selftests/arm64/Makefile
@@ -4,7 +4,7 @@
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),aarch64 arm64))
-ARM64_SUBTARGETS ?= tags signal pauth fp mte bti abi gcs
+ARM64_SUBTARGETS ?= tags signal pauth fp mte bti abi gcs poe
 else
 ARM64_SUBTARGETS :=
 endif
diff --git a/tools/testing/selftests/arm64/poe/.gitignore b/tools/testing/selftests/arm64/poe/.gitignore
new file mode 100644
index 000000000000..0dce4a3aa38b
--- /dev/null
+++ b/tools/testing/selftests/arm64/poe/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+poe_futex
diff --git a/tools/testing/selftests/arm64/poe/Makefile b/tools/testing/selftests/arm64/poe/Makefile
new file mode 100644
index 000000000000..2af2bbf3f6d3
--- /dev/null
+++ b/tools/testing/selftests/arm64/poe/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += $(KHDR_INCLUDES)
+TEST_GEN_PROGS := poe_futex
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/arm64/poe/poe_futex.c b/tools/testing/selftests/arm64/poe/poe_futex.c
new file mode 100644
index 000000000000..21a2e109ee43
--- /dev/null
+++ b/tools/testing/selftests/arm64/poe/poe_futex.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <linux/futex.h>
+#include <sys/syscall.h>
+
+#include "kselftest_harness.h"
+
+static int sys_pkey_alloc(unsigned long flags, unsigned long init_val)
+{
+	return syscall(__NR_pkey_alloc, flags, init_val);
+}
+
+static int sys_pkey_mprotect(void *ptr, size_t size, int prot, int pkey)
+{
+	return syscall(__NR_pkey_mprotect, ptr, size, prot, pkey);
+}
+
+static int futex_wake_op(uint32_t *uaddr, uint32_t val, uint32_t val2,
+			 uint32_t *uaddr2, uint32_t val3)
+{
+	return syscall(SYS_futex, uaddr, FUTEX_WAKE_OP, val, val2,
+		       uaddr2, val3);
+}
+
+/*
+ * Trigger some atomic uaccess on a page mapped with a non-default pkey.
+ *
+ * This ensures that such access is not mistakenly checked against the
+ * kernel's POR_EL1 register.
+ */
+TEST(poe_futex)
+{
+	int ret, pkey;
+	void *ptr;
+	size_t size = getpagesize();
+
+	pkey = sys_pkey_alloc(0, 0);
+
+	if (pkey == -1 && errno == ENOSPC)
+		SKIP(return, "pkeys are not supported");
+
+	ASSERT_GT(pkey, 0);
+
+	ptr = mmap(NULL, size, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+
+	ret = sys_pkey_mprotect(ptr, size, PROT_READ | PROT_WRITE, pkey);
+	ASSERT_EQ(ret, 0);
+
+	/*
+	 * There is no one to wake up so this syscall boils down to *(ptr+4) = 0
+	 * (arch_futex_atomic_op_inuser() called with FUTEX_OP_SET and op_arg=0).
+	 */
+	ret = futex_wake_op(ptr, 1, 1, ptr + sizeof(uint32_t), 0);
+	ASSERT_EQ(ret, 0);
+}
+
+TEST_HARNESS_MAIN

-- 
2.51.2