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

Cyril Hrubis
2026-02-20T10:41:56Z

Hi!
> 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);

The signal handle can be set once from the test setup().

And we have to reset the poison_fault_seen and sigbus_seen flags here so
that we actually test something with -i 2

> + 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;

Does LTP_VAR_USED(dummy) = page[0] work here instead of the volatile and
cast to the (void) ?

> + }
> +
> + 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
>
>
> --
> Mailing list info: https://lists.linux.it/listinfo/ltp

--
Cyril Hrubis
chrubis@suse.cz