[LTP] [PATCH v4] userfaultfd: Add test using UFFDIO_POISON

Ricardo Branco
2026-02-19T22:50:47Z

Signed-off-by: Ricardo Branco <rbranco@suse.de>
---
configure.ac | 1 +
include/lapi/userfaultfd.h | 13 ++
.../kernel/syscalls/userfaultfd/.gitignore | 1 +
.../kernel/syscalls/userfaultfd/Makefile | 1 +
.../syscalls/userfaultfd/userfaultfd06.c | 137 ++++++++++++++++++
5 files changed, 153 insertions(+)
create mode 100644 testcases/kernel/syscalls/userfaultfd/userfaultfd06.c

diff --git a/configure.ac b/configure.ac
index 7fa614dcb..94bcbcc98 100644
--- a/configure.ac
+++ b/configure.ac
@@ -278,6 +278,7 @@ AC_CHECK_TYPES([struct sockaddr_vm],,,[
])

AC_CHECK_TYPES([struct uffdio_move],,,[#include <linux/userfaultfd.h>])
+AC_CHECK_TYPES([struct uffdio_poison],,,[#include <linux/userfaultfd.h>])
AC_CHECK_TYPES([struct uffdio_writeprotect],,,[#include <linux/userfaultfd.h>])

# Tools knobs
diff --git a/include/lapi/userfaultfd.h b/include/lapi/userfaultfd.h
index 0c9e34c84..aab3890b7 100644
--- a/include/lapi/userfaultfd.h
+++ b/include/lapi/userfaultfd.h
@@ -233,6 +233,19 @@ struct uffdio_writeprotect {
};
#endif /* HAVE_STRUCT_UFFDIO_WRITEPROTECT */

+#ifndef HAVE_STRUCT_UFFDIO_POISON
+#define UFFD_FEATURE_POISON (1<<14)
+#define _UFFDIO_POISON (0x08)
+#define UFFDIO_POISON _IOWR(UFFDIO, _UFFDIO_POISON, \
+ struct uffdio_poison)
+struct uffdio_poison {
+ struct uffdio_range range;
+#define UFFDIO_POISON_MODE_DONTWAKE ((__u64)1<<0)
+ __u64 mode;
+ __s64 updated;
+};
+#endif /* HAVE_STRUCT_UFFDIO_POISON */
+
#define SAFE_USERFAULTFD(flags, retry) \
safe_userfaultfd(__FILE__, __LINE__, (flags), (retry))

diff --git a/testcases/kernel/syscalls/userfaultfd/.gitignore b/testcases/kernel/syscalls/userfaultfd/.gitignore
index fb2ae243b..bc32fdf3b 100644
--- a/testcases/kernel/syscalls/userfaultfd/.gitignore
+++ b/testcases/kernel/syscalls/userfaultfd/.gitignore
@@ -3,3 +3,4 @@
/userfaultfd03
/userfaultfd04
/userfaultfd05
+/userfaultfd06
diff --git a/testcases/kernel/syscalls/userfaultfd/Makefile b/testcases/kernel/syscalls/userfaultfd/Makefile
index 96650a65a..3252e47df 100644
--- a/testcases/kernel/syscalls/userfaultfd/Makefile
+++ b/testcases/kernel/syscalls/userfaultfd/Makefile
@@ -16,3 +16,4 @@ userfaultfd02: CFLAGS += -pthread
userfaultfd03: CFLAGS += -pthread
userfaultfd04: CFLAGS += -pthread
userfaultfd05: CFLAGS += -pthread
+userfaultfd06: CFLAGS += -pthread
diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
new file mode 100644
index 000000000..1f132d4d5
--- /dev/null
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 SUSE LLC
+ * Author: Ricardo Branco <rbranco@suse.com>
+ */
+
+/*\
+ * Force a pagefault event and handle it using :manpage:`userfaultfd(2)`
+ * from a different thread testing UFFDIO_POISON.
+ */
+
+#include "config.h"
+#include <poll.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <unistd.h>
+#include "tst_test.h"
+#include "tst_safe_macros.h"
+#include "tst_safe_pthread.h"
+#include "lapi/userfaultfd.h"
+
+static int page_size;
+static char *page;
+static int uffd;
+static int poison_fault_seen;
+static volatile int sigbus_seen;
+static sigjmp_buf jmpbuf;
+
+static void sigbus_handler(int sig)
+{
+ if (sig == SIGBUS) {
+ sigbus_seen = 1;
+ siglongjmp(jmpbuf, 1);
+ }
+}
+
+static void set_pages(void)
+{
+ page_size = sysconf(_SC_PAGE_SIZE);
+ page = SAFE_MMAP(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+}
+
+static void cleanup(void)
+{
+ if (page) {
+ SAFE_MUNMAP(page, page_size);
+ page = NULL;
+ }
+}
+
+static void *handle_thread(void)
+{
+ static struct uffd_msg msg;
+ struct uffdio_poison uffdio_poison = {};
+ struct pollfd pollfd;
+ int nready;
+
+ pollfd.fd = uffd;
+ pollfd.events = POLLIN;
+ nready = poll(&pollfd, 1, -1);
+ if (nready == -1)
+ tst_brk(TBROK | TERRNO, "Error on poll");
+
+ SAFE_READ(1, uffd, &msg, sizeof(msg));
+
+ if (msg.event != UFFD_EVENT_PAGEFAULT)
+ tst_brk(TFAIL, "Received unexpected UFFD_EVENT %d", msg.event);
+
+ tst_atomic_store(1, &poison_fault_seen);
+
+ /* Poison the page that triggered the fault */
+ uffdio_poison.range.start = msg.arg.pagefault.address & ~(page_size - 1);
+ uffdio_poison.range.len = page_size;
+
+ SAFE_IOCTL(uffd, UFFDIO_POISON, &uffdio_poison);
+
+ close(uffd);
+ return NULL;
+}
+
+static void run(void)
+{
+ pthread_t thr;
+ struct uffdio_api uffdio_api = {};
+ struct uffdio_register uffdio_register;
+ struct sigaction sa = {};
+ volatile char dummy;
+
+ sa.sa_handler = sigbus_handler;
+ sigemptyset(&sa.sa_mask);
+ SAFE_SIGACTION(SIGBUS, &sa, NULL);
+
+ set_pages();
+
+ uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
+
+ uffdio_api.api = UFFD_API;
+ uffdio_api.features = UFFD_FEATURE_POISON;
+
+ SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
+
+ if (!(uffdio_api.features & UFFD_FEATURE_POISON))
+ tst_brk(TCONF, "UFFD_FEATURE_POISON not supported");
+
+ uffdio_register.range.start = (unsigned long) page;
+ uffdio_register.range.len = page_size;
+ uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+
+ SAFE_IOCTL(uffd, UFFDIO_REGISTER, &uffdio_register);
+
+ SAFE_PTHREAD_CREATE(&thr, NULL, (void *) handle_thread, NULL);
+
+ /* Try to read from the page: should trigger fault, get poisoned, then SIGBUS */
+ if (sigsetjmp(jmpbuf, 1) == 0) {
+ dummy = page[0];
+ (void)dummy;
+ }
+
+ SAFE_PTHREAD_JOIN(thr, NULL);
+
+ int poisoned = tst_atomic_load(&poison_fault_seen);
+
+ if (poisoned && sigbus_seen)
+ tst_res(TPASS, "POISON successfully triggered SIGBUS");
+ else if (poison_fault_seen && !sigbus_seen)
+ tst_res(TFAIL, "POISON fault seen but no SIGBUS received");
+ else if (!poison_fault_seen && sigbus_seen)
+ tst_res(TFAIL, "SIGBUS received but no poison fault seen");
+ else
+ tst_res(TFAIL, "No poison fault or SIGBUS observed");
+}
+
+static struct tst_test test = {
+ .test_all = run,
+ .cleanup = cleanup,
+};
--
2.53.0