[PATCH 2/2] powerpc/selftests: Check endianness on trap in TM
Gustavo Romero
gromero at linux.vnet.ibm.com
Mon Jan 1 10:20:46 AEDT 2018
Add a selftest to check if endianness is flipped inadvertently to BE
(MSR.LE set to zero) on BE and LE machines when a trap is caught in
transactional mode and load_fp and load_vec are zero, i.e. when MSR.FP
and MSR.VEC are zeroed (disabled).
Signed-off-by: Gustavo Romero <gromero at linux.vnet.ibm.com>
---
tools/testing/selftests/powerpc/tm/.gitignore | 1 +
tools/testing/selftests/powerpc/tm/Makefile | 3 +-
tools/testing/selftests/powerpc/tm/tm-trap.c | 329 ++++++++++++++++++++++++++
3 files changed, 332 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/powerpc/tm/tm-trap.c
diff --git a/tools/testing/selftests/powerpc/tm/.gitignore b/tools/testing/selftests/powerpc/tm/.gitignore
index 241a4a4..bb90d4b 100644
--- a/tools/testing/selftests/powerpc/tm/.gitignore
+++ b/tools/testing/selftests/powerpc/tm/.gitignore
@@ -13,3 +13,4 @@ tm-signal-context-chk-vmx
tm-signal-context-chk-vsx
tm-vmx-unavail
tm-unavailable
+tm-trap
diff --git a/tools/testing/selftests/powerpc/tm/Makefile b/tools/testing/selftests/powerpc/tm/Makefile
index 8ed6f8c..a234539 100644
--- a/tools/testing/selftests/powerpc/tm/Makefile
+++ b/tools/testing/selftests/powerpc/tm/Makefile
@@ -3,7 +3,7 @@ SIGNAL_CONTEXT_CHK_TESTS := tm-signal-context-chk-gpr tm-signal-context-chk-fpu
tm-signal-context-chk-vmx tm-signal-context-chk-vsx
TEST_GEN_PROGS := tm-resched-dscr tm-syscall tm-signal-msr-resv tm-signal-stack \
- tm-vmxcopy tm-fork tm-tar tm-tmspr tm-vmx-unavail tm-unavailable \
+ tm-vmxcopy tm-fork tm-tar tm-tmspr tm-vmx-unavail tm-unavailable tm-trap \
$(SIGNAL_CONTEXT_CHK_TESTS)
include ../../lib.mk
@@ -18,6 +18,7 @@ $(OUTPUT)/tm-tmspr: CFLAGS += -pthread
$(OUTPUT)/tm-vmx-unavail: CFLAGS += -pthread -m64
$(OUTPUT)/tm-resched-dscr: ../pmu/lib.o
$(OUTPUT)/tm-unavailable: CFLAGS += -O0 -pthread -m64 -Wno-error=uninitialized -mvsx
+$(OUTPUT)/tm-trap: CFLAGS += -O0 -pthread -m64
SIGNAL_CONTEXT_CHK_TESTS := $(patsubst %,$(OUTPUT)/%,$(SIGNAL_CONTEXT_CHK_TESTS))
$(SIGNAL_CONTEXT_CHK_TESTS): tm-signal.S
diff --git a/tools/testing/selftests/powerpc/tm/tm-trap.c b/tools/testing/selftests/powerpc/tm/tm-trap.c
new file mode 100644
index 0000000..5d92c23
--- /dev/null
+++ b/tools/testing/selftests/powerpc/tm/tm-trap.c
@@ -0,0 +1,329 @@
+/*
+ * Copyright 2017, Gustavo Romero, IBM Corp.
+ * Licensed under GPLv2.
+ *
+ * Check if thread endianness is flipped inadvertently to BE on trap
+ * caught in TM whilst MSR.FP and MSR.VEC are zero (i.e. just after
+ * load_fp and load_vec overflowed).
+ *
+ * The issue can be checked on LE machines simply by zeroing load_fp
+ * and load_vec and then causing a trap in TM. Since the endianness
+ * changes to BE on return from the signal handler, 'nop' is
+ * thread as an illegal instruction in following sequence:
+ * tbegin.
+ * beq 1f
+ * trap
+ * tend.
+ * 1: nop
+ *
+ * However, although the issue is also present on BE machines, it's a
+ * bit trickier to check it on BE machines because MSR.LE bit is set
+ * to zero which determines a BE endianness that is the native
+ * endianness on BE machines, so nothing notably critical happens,
+ * i.e. no illegal instruction is observed immediately after returning
+ * from the signal handler (as it happens on LE machines). Thus to test
+ * it on BE machines LE endianness is forced after a first trap and then
+ * the endianness is verified on subsequent traps to determine if the
+ * endianness "flipped back" to the native endianness (BE).
+ */
+
+#define _GNU_SOURCE
+#include <error.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <htmintrin.h>
+#include <inttypes.h>
+#include <pthread.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdbool.h>
+
+#include "tm.h"
+#include "utils.h"
+
+#define pr_error(error_code, format, ...) \
+ error_at_line(1, error_code, __FILE__, __LINE__, format, ##__VA_ARGS__)
+
+#define MSR_LE 1UL
+#define LE 1UL
+
+pthread_t t0_ping;
+pthread_t t1_pong;
+
+int exit_from_pong;
+
+int trap_event;
+int le;
+
+bool success;
+
+void trap_signal_handler(int signo, siginfo_t *si, void *uc)
+{
+ ucontext_t *ucp = uc;
+ uint64_t thread_endianness;
+
+ /* Get thread endianness: extract bit LE from MSR */
+ thread_endianness = MSR_LE & ucp->uc_mcontext.gp_regs[PT_MSR];
+
+ /***
+ * Little-Endian Machine
+ */
+
+ if (le) {
+ /* First trap event */
+ if (trap_event == 0) {
+ /* Do nothing. Since it is returning from this trap
+ * event that endianness is flipped by the bug, so just
+ * let the process return from the signal handler and
+ * check on the second trap event if endianness is
+ * flipped or not.
+ */
+ }
+ /* Second trap event */
+ else if (trap_event == 1) {
+ /*
+ * Since trap was caught in TM on first trap event, if
+ * endianness was still LE (not flipped inadvertently)
+ * after returning from the signal handler instruction
+ * (1) is executed (basically a 'nop'), as it's located
+ * at address of tbegin. +4 (rollback addr). As (1) on
+ * LE endianness does in effect nothing, instruction (2)
+ * is then executed again as 'trap', generating a second
+ * trap event (note that in that case 'trap' is caught
+ * not in transacional mode). On te other hand, if after
+ * the return from the signal handler the endianness in-
+ * advertently flipped, instruction (1) is tread as a
+ * branch instruction, i.e. b .+8, hence instruction (3)
+ * and (4) are executed (tbegin.; trap;) and we get sim-
+ * ilaly on the trap signal handler, but now in TM mode.
+ * Either way, it's now possible to check the MSR LE bit
+ * once in the trap handler to verify if endianness was
+ * flipped or not after the return from the second trap
+ * event. If endianness is flipped, the bug is present.
+ * Finally, getting a trap in TM mode or not is just
+ * worth noting because it affects the math to determine
+ * the offset added to the NIP on return: the NIP for a
+ * trap caught in TM is the rollback address, i.e. the
+ * next instruction after 'tbegin.', whilst the NIP for
+ * a trap caught in non-transactional mode is the very
+ * same address of the 'trap' instruction that generated
+ * the trap event.
+ */
+
+ if (thread_endianness == LE) {
+ /* Go to 'success', i.e. instruction (6) */
+ ucp->uc_mcontext.gp_regs[PT_NIP] += 16;
+ } else {
+ /*
+ * Thread endianness is BE, so it flipped
+ * inadvertently. Thus we flip back to LE and
+ * set NIP to go to 'failure', instruction (5).
+ */
+ ucp->uc_mcontext.gp_regs[PT_MSR] |= 1UL;
+ ucp->uc_mcontext.gp_regs[PT_NIP] += 4;
+ }
+ }
+ }
+
+ /***
+ * Big-Endian Machine
+ */
+
+ else {
+ /* First trap event */
+ if (trap_event == 0) {
+ /*
+ * Force thread endianness to be LE. Instructions (1),
+ * (3), and (4) will be executed, generating a second
+ * trap in TM mode.
+ */
+ ucp->uc_mcontext.gp_regs[PT_MSR] |= 1UL;
+ }
+ /* Second trap event */
+ else if (trap_event == 1) {
+ /*
+ * Do nothing. If bug is present on return from this
+ * second trap event endianness will flip back "automat-
+ * ically" to BE, otherwise thread endianness will
+ * continue to be LE, just as it was set above.
+ */
+ }
+ /* A third trap event */
+ else {
+ /*
+ * Once here it means that after returning from the sec-
+ * ond trap event instruction (4) (trap) was executed
+ * as LE, generating a third trap event. In that case
+ * endianness is still LE as set on return from the
+ * first trap event, hence no bug. Otherwise, bug
+ * flipped back to BE on return from the second trap
+ * event and instruction (4) was executed as 'tdi' (so
+ * basically a 'nop') and branch to 'failure' in
+ * instruction (5) was taken to indicate failure and we
+ * never get here.
+ */
+
+ /*
+ * Flip back to BE and go to instruction (6), i.e. go to
+ * 'success'.
+ */
+ ucp->uc_mcontext.gp_regs[PT_MSR] &= ~1UL;
+ ucp->uc_mcontext.gp_regs[PT_NIP] += 8;
+ }
+ }
+
+ trap_event++;
+}
+
+void usr1_signal_handler(int signo, siginfo_t *si, void *not_used)
+{
+ /* Got a USR1 signal from ping(), so just tell pong() to exit */
+ exit_from_pong = 1;
+}
+
+void *ping(void *not_used)
+{
+ uint64_t i;
+
+ trap_event = 0;
+
+ /*
+ * Wait an amount of context switches so load_fp and load_vec overflows
+ * and MSR_[FP|VEC|V] is 0.
+ */
+ for (i = 0; i < 1024*1024*512; i++)
+ ;
+
+ asm goto(
+ /*
+ * [NA] means "Native Endianness", i.e. it tells how a
+ * instruction is executed on machine's native endianness (in
+ * other words, native endianness matches kernel endianness).
+ * [OP] means "Opposite Endianness", i.e. on a BE machine, it
+ * tells how a instruction is executed as a LE instruction; con-
+ * versely, on a LE machine, it tells how a instruction is
+ * executed as a BE instruction. When [NA] is omitted, it means
+ * that the native interpretation of a given instruction is not
+ * relevant for the test. Likewise when [OP] is omitted.
+ */
+
+ " tbegin. ;" /* (0) tbegin. [NA] */
+ " tdi 0, 0, 0x48;" /* (1) nop [NA]; b (3) [OP] */
+ " trap ;" /* (2) trap [NA] */
+ ".long 0x1D05007C;" /* (3) tbegin. [OP] */
+ ".long 0x0800E07F;" /* (4) trap [OP]; nop [NA] */
+ " b %l[failure] ;" /* (5) b [NA]; MSR.LE flipped (bug) */
+ " b %l[success] ;" /* (6) b [NA]; MSR.LE did not flip (ok)*/
+
+ : : : : failure, success);
+
+failure:
+ success = false;
+ goto exit_from_ping;
+
+success:
+ success = true;
+
+exit_from_ping:
+ /* Tell pong() to exit before leaving */
+ pthread_kill(t1_pong, SIGUSR1);
+ return NULL;
+}
+
+void *pong(void *not_used)
+{
+ while (!exit_from_pong)
+ /*
+ * Induce context switches on ping() thread
+ * until ping() finishes its job and signs
+ * to exit from this loop.
+ */
+ sched_yield();
+
+ return NULL;
+}
+
+int tm_trap_test(void)
+{
+ uint16_t k = 1;
+
+ int rc;
+
+ pthread_attr_t attr;
+ cpu_set_t cpuset;
+
+ struct sigaction trap_sa;
+
+ trap_sa.sa_flags = SA_SIGINFO;
+ trap_sa.sa_sigaction = trap_signal_handler;
+ sigaction(SIGTRAP, &trap_sa, NULL);
+
+ struct sigaction usr1_sa;
+
+ usr1_sa.sa_flags = SA_SIGINFO;
+ usr1_sa.sa_sigaction = usr1_signal_handler;
+ sigaction(SIGUSR1, &usr1_sa, NULL);
+
+ /* Set only CPU 0 in the mask. Both threads will be bound to cpu 0. */
+ CPU_ZERO(&cpuset);
+ CPU_SET(0, &cpuset);
+
+ /* Init pthread attribute */
+ rc = pthread_attr_init(&attr);
+ if (rc)
+ pr_error(rc, "pthread_attr_init()");
+
+ /*
+ * Bind thread ping() and pong() both to CPU 0 so they ping-pong and
+ * speed up context switches on ping() thread, speeding up the load_fp
+ * and load_vec overflow.
+ */
+ rc = pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &cpuset);
+ if (rc)
+ pr_error(rc, "pthread_attr_setaffinity()");
+
+ /* Figure out the machine endianness */
+ le = (int) *(uint8_t *)&k;
+
+ printf("%s machine detected. Checking if endianness flips %s",
+ le ? "Little-Endian" : "Big-Endian",
+ "inadvertently on trap in TM... ");
+
+ rc = fflush(0);
+ if (rc)
+ pr_error(rc, "fflush()");
+
+ /* Launch ping() */
+ rc = pthread_create(&t0_ping, &attr, ping, NULL);
+ if (rc)
+ pr_error(rc, "pthread_create()");
+
+ exit_from_pong = 0;
+
+ /* Launch pong() */
+ rc = pthread_create(&t1_pong, &attr, pong, NULL);
+ if (rc)
+ pr_error(rc, "pthread_create()");
+
+ rc = pthread_join(t0_ping, NULL);
+ if (rc)
+ pr_error(rc, "pthread_join()");
+
+ rc = pthread_join(t1_pong, NULL);
+ if (rc)
+ pr_error(rc, "pthread_join()");
+
+ if (success) {
+ printf("no.\n"); /* no, endianness did not flip inadvertently */
+ return EXIT_SUCCESS;
+ }
+
+ printf("yes!\n"); /* yes, endianness did flip inadvertently */
+ return EXIT_FAILURE;
+}
+
+int main(int argc, char **argv)
+{
+ return test_harness(tm_trap_test, "tm_trap_test");
+}
--
2.7.4
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