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Subject[PATCH 15/15] x86/split_lock: Add split lock user space test in selftest
Date
The test generates split locked access from user space. If #AC
exception is enabled for split lock, a SIGBUS is delivered
to the test.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
tools/testing/selftests/x86/Makefile | 3 +-
tools/testing/selftests/x86/split_lock_user_test.c | 187 +++++++++++++++++++++
2 files changed, 189 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/x86/split_lock_user_test.c

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index d744991c0f4f..19d65729b100 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -11,7 +11,8 @@ CAN_BUILD_X86_64 := $(shell ./check_cc.sh $(CC) trivial_64bit_program.c)

TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt test_mremap_vdso \
check_initial_reg_state sigreturn iopl mpx-mini-test ioperm \
- protection_keys test_vdso test_vsyscall
+ protection_keys test_vdso test_vsyscall \
+ split_lock_user_test
TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \
test_FCMOV test_FCOMI test_FISTTP \
vdso_restorer
diff --git a/tools/testing/selftests/x86/split_lock_user_test.c b/tools/testing/selftests/x86/split_lock_user_test.c
new file mode 100644
index 000000000000..e6f3367dfb6b
--- /dev/null
+++ b/tools/testing/selftests/x86/split_lock_user_test.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018 Intel Corporation
+ * Author: Fenghua Yu <fenghua.yu@intel.com>
+ *
+ * Pre-request:
+ * Kernel is built with CONFIG_SPLIT_LOCK_AC=y.
+ * Split lock is enabled. If not, enable it by:
+ * #echo 1 >/sys/kernel/split_lock/enable
+ *
+ * Usage:
+ * Run the test alone and it should show:
+ * TEST PASS: locked instruction is re-executed.
+ * TEST PASS: Caught SIGBUS/#AC due to split locked access
+ *
+ * Or launch the test from perf and watch "split_lock_user" event count.
+ * #/perf stat -e exceptions:split_lock* /root/split_lock_user_test_64
+ * TEST PASS: locked instruction is re-executed.
+ * TEST PASS: Caught SIGBUS/#AC due to split locked access
+ *
+ * Performance counter stats for '/root/split_lock_user_test_64':
+ *
+ * 1 exceptions:split_lock_user
+ * 0 exceptions:split_lock_kernel
+ *
+ * 1.000893458 seconds time elapsed
+ */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+
+int split_lock_exception;
+
+void catch_sigbus(int sig)
+{
+ split_lock_exception = 1;
+ printf("TEST PASS: Caught SIGBUS/#AC due to split locked access\n");
+
+ exit(-1);
+}
+
+int split_lock_ac_enabled(void)
+{
+ int fd, enable, ret;
+ char buf[16];
+
+ fd = open("/sys/kernel/split_lock/enable", O_RDONLY);
+ if (fd < 0)
+ return 0;
+
+ if (read(fd, buf, sizeof(int)) < 0) {
+ ret = 0;
+ goto out;
+ }
+
+ enable = atoi(buf);
+ if (enable == 1)
+ ret = 1;
+ else
+ ret = 0;
+
+out:
+ close(fd);
+
+ return ret;
+}
+
+int setup_user_mode(char *user_mode_reaction)
+{
+ ssize_t count;
+ int fd;
+
+ if (strcmp(user_mode_reaction, "sigbus") &&
+ strcmp(user_mode_reaction, "re-execute"))
+ return -1;
+
+ fd = open("/sys/kernel/split_lock/user_mode", O_RDWR);
+ if (fd < 0)
+ return -1;
+
+ count = write(fd, user_mode_reaction, strlen(user_mode_reaction));
+ if (count != strlen(user_mode_reaction))
+ return -1;
+
+ close(fd);
+
+ return 0;
+}
+
+void do_split_locked_inst(int a, int b, int *iptr)
+{
+ /*
+ * Since eax is equal to *iptr, the instruction loads value in b
+ * (i.e. 11) into iptr. If the instruction is executed correctly,
+ * the content of *iptr is changed * to 11 from previous value 1.
+ *
+ * Accessing iptr cross two cache lines will trigger #AC in hardware
+ * and kernel either delivers SIGBUS to this process or re-execute
+ * the instruction depending on /sys/kernel/split_lock/user_mode
+ * setting.
+ */
+ asm volatile ("movl %1, %%eax\n\t"
+ "movl %1, %0\n\t"
+ "lock\n cmpxchgl %2, %0\n\t"
+ : "=m" (*iptr)
+ : "r"(a), "r"(b)
+ : "%eax");
+}
+
+void test_re_execute(int a, int b, int *iptr)
+{
+ setup_user_mode("re-execute");
+
+ /* The locked instruction triggers #AC and then it's re-executed. */
+ do_split_locked_inst(a, b, iptr);
+
+ if (*iptr == b) {
+ printf("TEST PASS: locked instruction is re-executed.\n");
+ } else {
+ printf("TEST FAIL: No #AC exception is caught and ");
+ printf("instruction is not executed correctly.\n");
+ }
+}
+
+void test_sigbus(int a, int b, int *iptr)
+{
+ setup_user_mode("sigbus");
+
+ /*
+ * The locked instruction triggers #AC and kernel delivers SIGBUS
+ * to this process.
+ */
+ do_split_locked_inst(a, b, iptr);
+}
+
+int main(int argc, char **argv)
+{
+ int *iptr, a = 10, b = 11;
+ char *cptr;
+
+ if (!split_lock_ac_enabled()) {
+ printf("#AC exception for split lock is NOT enabled!!\n");
+ printf("Please make sure split lock feature is supported,\n");
+ printf("CONFIG_SPLIT_LOCK_AC is turned on,\n");
+ printf("and /sys/kernel/split_lock/enable is 1 before test!\n");
+
+ return 0;
+ }
+
+ signal(SIGBUS, catch_sigbus);
+
+ /*
+ * Enable Alignment Checking on x86_64.
+ * This will generate alignment check on not only split lock but also
+ * on any misalignment.
+ * Turn on this for reference only.
+ */
+ /* __asm__("pushf\norl $0x40000,(%rsp)\npopf"); */
+
+ /* aligned_alloc() provides 64-byte aligned memory */
+ cptr = (char *)aligned_alloc(64, 128);
+
+ /* Increment the pointer by 61, making it misaligned */
+ iptr = (int *)(cptr + 61);
+
+ /* Initial value in iptr is 1. */
+ *iptr = 1;
+
+ test_re_execute(a, b, iptr);
+ /*
+ * The split lock is disabled after the last locked instruction is
+ * re-executed.
+ *
+ * Wait for the split lock is re-enabled again before next test.
+ */
+ sleep(1);
+ test_sigbus(a, b, iptr);
+
+ free(cptr);
+
+ return 0;
+}
--
2.5.0
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