Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Andrea Cervesato via ltp <ltp@lists.linux.it>]

Hi!

On Wed Feb 18, 2026 at 2:50 PM CET, Ricardo Branco wrote:
> 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      | 134 ++++++++++++++++++
>  5 files changed, 150 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..c4546acce
> --- /dev/null
> +++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
> @@ -0,0 +1,134 @@
> +// 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 volatile 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 reset_pages(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);
> +
> +	poison_fault_seen = 1;
> +
> +	/* 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);
> +
> +	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);
> +	reset_pages();

This should also go into a cleanup(), otherwise if other syscalls will
fail (ioctl for instance), memory will be lost.

> +
> +	if (poison_fault_seen && 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,
> +	.min_kver = "6.6",

This is not needed, we should use UFFDIO_API instead, in order to verify
that UFFD_FEATURE_POISON is present and eventually TCONF.


Also, if I run checkpatch.pl on the code I get:

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#25: FILE: userfaultfd06.c:25:
+static volatile int poison_fault_seen;

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#26: FILE: userfaultfd06.c:26:
+static volatile int sigbus_seen;

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#88: FILE: userfaultfd06.c:88:
+       volatile char dummy;

WARNING: braces {} are not necessary for any arm of this statement
#120: FILE: userfaultfd06.c:120:
+       if (poison_fault_seen && sigbus_seen) {
[...]
+       } else if (poison_fault_seen && !sigbus_seen) {
[...]
+       } else if (!poison_fault_seen && sigbus_seen) {
[...]
+       } else {
[...]

total: 0 errors, 4 warnings, 134 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

userfaultfd06.c has style problems, please review.

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.

If you have `b4`, please run `b4 prep --check` before sending the patch.

-- 
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com


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