This test triggers a TM Bad Thing by raising a signal in transactional state
and forcing a pagefault to happen in kernelspace when the kernel signal
handling code first touches the user signal stack.
This is inspired by the test tm-signal-context-force-tm but uses userfaultfd to
make the test deterministic. While this test always triggers the bug in one
run, I had to execute tm-signal-context-force-tm several times (the test runs
5000 times each execution) to trigger the same bug.
tm-signal-context-force-tm is kept instead of replaced because, while this test
is more reliable and triggers the same bug, tm-signal-context-force-tm has a
better coverage, in the sense that by running the test several times it might
trigger the pagefault and/or be preempted at different places.
Signed-off-by: Gustavo Luiz Duarte <gustav...@linux.ibm.com>
---
tools/testing/selftests/powerpc/tm/.gitignore | 1 +
tools/testing/selftests/powerpc/tm/Makefile | 3 +-
.../powerpc/tm/tm-signal-pagefault.c | 272 ++++++++++++++++++
3 files changed, 275 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c
diff --git a/tools/testing/selftests/powerpc/tm/.gitignore
b/tools/testing/selftests/powerpc/tm/.gitignore
index 98f2708d86cc..e1c72a4a3e91 100644
--- a/tools/testing/selftests/powerpc/tm/.gitignore
+++ b/tools/testing/selftests/powerpc/tm/.gitignore
@@ -13,6 +13,7 @@ tm-signal-context-chk-vmx
tm-signal-context-chk-vsx
tm-signal-context-force-tm
tm-signal-sigreturn-nt
+tm-signal-pagefault
tm-vmx-unavail
tm-unavailable
tm-trap
diff --git a/tools/testing/selftests/powerpc/tm/Makefile
b/tools/testing/selftests/powerpc/tm/Makefile
index b15a1a325bd0..b1d99736f8b8 100644
--- a/tools/testing/selftests/powerpc/tm/Makefile
+++ b/tools/testing/selftests/powerpc/tm/Makefile
@@ -5,7 +5,7 @@ SIGNAL_CONTEXT_CHK_TESTS := tm-signal-context-chk-gpr
tm-signal-context-chk-fpu
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-trap \
$(SIGNAL_CONTEXT_CHK_TESTS) tm-sigreturn tm-signal-sigreturn-nt \
- tm-signal-context-force-tm tm-poison
+ tm-signal-context-force-tm tm-poison tm-signal-pagefault
top_srcdir = ../../../../..
include ../../lib.mk
@@ -22,6 +22,7 @@ $(OUTPUT)/tm-resched-dscr: ../pmu/lib.c
$(OUTPUT)/tm-unavailable: CFLAGS += -O0 -pthread -m64
-Wno-error=uninitialized -mvsx
$(OUTPUT)/tm-trap: CFLAGS += -O0 -pthread -m64
$(OUTPUT)/tm-signal-context-force-tm: CFLAGS += -pthread -m64
+$(OUTPUT)/tm-signal-pagefault: CFLAGS += -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-signal-pagefault.c
b/tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c
new file mode 100644
index 000000000000..3a2166101d94
--- /dev/null
+++ b/tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c
@@ -0,0 +1,272 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2020, Gustavo Luiz Duarte, IBM Corp.
+ *
+ * This test starts a transaction and triggers a signal, forcing a pagefault to
+ * happen when the kernel signal handling code touches the user signal stack.
+ *
+ * In order to avoid pre-faulting the signal stack memory and to force the
+ * pagefault to happen precisely in the kernel signal handling code, the
+ * pagefault handling is done in userspace using the userfaultfd facility.
+ *
+ * Further pagefaults are triggered by crafting the signal handler's ucontext
+ * to point to additional memory regions managed by the userfaultfd, so using
+ * the same mechanism used to avoid pre-faulting the signal stack memory.
+ *
+ * On failure (bug is present) kernel crashes or never returns control back to
+ * userspace. If bug is not present, tests completes almost immediately.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <linux/userfaultfd.h>
+#include <poll.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <pthread.h>
+#include <signal.h>
+
+#include "tm.h"
+
+
+#define UF_MEM_SIZE 655360 /* 10 x 64k pages */
+
+/* Memory handled by userfaultfd */
+static char *uf_mem;
+static size_t uf_mem_offset = 0;
+
+/*
+ * Data that will be copied into the faulting pages (instead of zero-filled
+ * pages). This is used to make the test more reliable and avoid segfaulting
+ * when we return from the signal handler. Since we are making the signal
+ * handler's ucontext point to newly allocated memory, when that memory is
+ * paged-in it will contain the expected content.
+ */
+static char backing_mem[UF_MEM_SIZE];
+
+static size_t pagesize;
+
+/*
+ * Return a chunk of at least 'size' bytes of memory that will be handled by
+ * userfaultfd. If 'backing_data' is not NULL, its content will be save to
+ * 'backing_mem' and then copied into the faulting pages when the page fault
+ * is handled.
+ */
+void *get_uf_mem(size_t size, void *backing_data)
+{
+ void *ret;
+
+ if (uf_mem_offset + size > UF_MEM_SIZE) {
+ fprintf(stderr, "Requesting more uf_mem than expected!\n");
+ exit(EXIT_FAILURE);
+ }
+
+ ret = &uf_mem[uf_mem_offset];
+
+ /* Save the data that will be copied into the faulting page */
+ if (backing_data != NULL)
+ memcpy(&backing_mem[uf_mem_offset], backing_data, size);
+
+ /* Reserve the requested amount of uf_mem */
+ uf_mem_offset += size;
+ /* Keep uf_mem_offset aligned to the page size (round up) */
+ uf_mem_offset = (uf_mem_offset + pagesize - 1) & ~(pagesize - 1);
+
+ return ret;
+}
+
+void *fault_handler_thread(void *arg)
+{
+ struct uffd_msg msg; /* Data read from userfaultfd */
+ long uffd; /* userfaultfd file descriptor */
+ struct uffdio_copy uffdio_copy;
+ struct pollfd pollfd;
+ ssize_t nread, offset;
+
+ uffd = (long) arg;
+
+ for (;;) {
+ pollfd.fd = uffd;
+ pollfd.events = POLLIN;
+ if (poll(&pollfd, 1, -1) == -1) {
+ perror("poll() failed");
+ exit(EXIT_FAILURE);
+ }
+
+ nread = read(uffd, &msg, sizeof(msg));
+ if (nread == 0) {
+ fprintf(stderr, "read(): EOF on userfaultfd\n");
+ exit(EXIT_FAILURE);
+ }
+
+ if (nread == -1) {
+ perror("read() failed");
+ exit(EXIT_FAILURE);
+ }
+
+ /* We expect only one kind of event */
+ if (msg.event != UFFD_EVENT_PAGEFAULT) {
+ fprintf(stderr, "Unexpected event on userfaultfd\n");
+ exit(EXIT_FAILURE);
+ }
+
+ /*
+ * We need to handle page faults in units of pages(!).
+ * So, round faulting address down to page boundary.
+ */
+ uffdio_copy.dst = msg.arg.pagefault.address & ~(pagesize-1);
+
+ offset = (char *) uffdio_copy.dst - uf_mem;
+ uffdio_copy.src = (unsigned long) &backing_mem[offset];
+
+ uffdio_copy.len = pagesize;
+ uffdio_copy.mode = 0;
+ uffdio_copy.copy = 0;
+ if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy) == -1) {
+ perror("ioctl-UFFDIO_COPY failed");
+ exit(EXIT_FAILURE);
+ }
+ }
+}
+
+void setup_uf_mem(void)
+{
+ long uffd; /* userfaultfd file descriptor */
+ pthread_t thr;
+ struct uffdio_api uffdio_api;
+ struct uffdio_register uffdio_register;
+ int ret;
+
+ pagesize = sysconf(_SC_PAGE_SIZE);
+
+ /* Create and enable userfaultfd object */
+ uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+ if (uffd == -1) {
+ perror("userfaultfd() failed");
+ exit(EXIT_FAILURE);
+ }
+ uffdio_api.api = UFFD_API;
+ uffdio_api.features = 0;
+ if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1) {
+ perror("ioctl-UFFDIO_API failed");
+ exit(EXIT_FAILURE);
+ }
+
+ /*
+ * Create a private anonymous mapping. The memory will be demand-zero
+ * paged, that is, not yet allocated. When we actually touch the memory
+ * the related page will be allocated via the userfaultfd mechanism.
+ */
+ uf_mem = mmap(NULL, UF_MEM_SIZE, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (uf_mem == MAP_FAILED) {
+ perror("mmap() failed");
+ exit(EXIT_FAILURE);
+ }
+
+ /*
+ * Register the memory range of the mapping we've just mapped to be
+ * handled by the userfaultfd object. In 'mode' we request to track
+ * missing pages (i.e. pages that have not yet been faulted-in).
+ */
+ uffdio_register.range.start = (unsigned long) uf_mem;
+ uffdio_register.range.len = UF_MEM_SIZE;
+ uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+ if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) {
+ perror("ioctl-UFFDIO_REGISTER");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Create a thread that will process the userfaultfd events */
+ ret = pthread_create(&thr, NULL, fault_handler_thread, (void *) uffd);
+ if (ret != 0) {
+ fprintf(stderr, "pthread_create(): Error. Returned %d\n", ret);
+ exit(EXIT_FAILURE);
+ }
+}
+
+/*
+ * Assumption: the signal was delivered while userspace was in transactional or
+ * suspended state, i.e. uc->uc_link != NULL.
+ */
+void signal_handler(int signo, siginfo_t *si, void *uc)
+{
+ ucontext_t *ucp = uc;
+
+ /* Skip 'trap' after returning, otherwise we get a SIGTRAP again */
+ ucp->uc_link->uc_mcontext.regs->nip += 4;
+
+ ucp->uc_mcontext.v_regs =
+ get_uf_mem(sizeof(elf_vrreg_t), ucp->uc_mcontext.v_regs);
+
+ ucp->uc_link->uc_mcontext.v_regs =
+ get_uf_mem(sizeof(elf_vrreg_t),
ucp->uc_link->uc_mcontext.v_regs);
+
+ ucp->uc_link = get_uf_mem(sizeof(ucontext_t), ucp->uc_link);
+}
+
+int tm_signal_pagefault(void)
+{
+ struct sigaction sa;
+ stack_t ss;
+
+ SKIP_IF(!have_htm());
+
+ setup_uf_mem();
+
+ /*
+ * Set an alternative stack that will generate a page fault when the
+ * signal is raised. The page fault will be treated via userfaultfd,
+ * i.e. via fault_handler_thread.
+ */
+ ss.ss_sp = get_uf_mem(SIGSTKSZ, NULL);
+ ss.ss_size = SIGSTKSZ;
+ ss.ss_flags = 0;
+ if (sigaltstack(&ss, NULL) == -1) {
+ perror("sigaltstack() failed");
+ exit(EXIT_FAILURE);
+ }
+
+ sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+ sa.sa_sigaction = signal_handler;
+ if (sigaction(SIGTRAP, &sa, NULL) == -1) {
+ perror("sigaction() failed");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Trigger a SIGTRAP in transactional state */
+ asm __volatile__(
+ "tbegin.;"
+ "beq 1f;"
+ "trap;"
+ "1: ;"
+ : : : "memory");
+
+ /* Trigger a SIGTRAP in suspended state */
+ asm __volatile__(
+ "tbegin.;"
+ "beq 1f;"
+ "tsuspend.;"
+ "trap;"
+ "tresume.;"
+ "1: ;"
+ : : : "memory");
+
+ return EXIT_SUCCESS;
+}
+
+int main(int argc, char **argv)
+{
+ /*
+ * Depending on kernel config, the TM Bad Thing might not result in a
+ * crash, instead the kernel never returns control back to userspace, so
+ * set a tight timeout. If the test passes it completes almost
+ * immediately.
+ */
+ test_harness_set_timeout(2);
+ return test_harness(tm_signal_pagefault, "tm_signal_pagefault");
+}
