On Wed, Mar 24, 2021 at 1:41 PM Lokesh Gidra <lokeshgidra@xxxxxxxxxx> wrote:
>
>
>
> On Wed, Mar 24, 2021 at 5:56 PM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
>>
>> On some old kernels (think RHEL-7) __NR_userfaultfd may not be defined
>> on certain arches, even though the <linux/userfaultfd.h> header is
>> available. To avoid build errors in such environments, abstract the
>> userfaultfd syscall into a helper function and make it fail with ENOSYS
>> when __NR_userfaultfd is not defined.
>>
>> Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
>
>
> Reviewed-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Thanks!
>
> Thanks for this fix.
>
> BTW, does it make sense to keep this test enabled on old kernels which don't have SELinux support for userfaultfd?
No, it doesn't - that's why I made it return ENOSYS in this case,
which will lead to the test being skipped.
>>
>> ---
>> tests/userfaultfd/userfaultfd.c | 17 ++++++++++++++---
>> 1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/tests/userfaultfd/userfaultfd.c b/tests/userfaultfd/userfaultfd.c
>> index a283a83..dd3a9f3 100644
>> --- a/tests/userfaultfd/userfaultfd.c
>> +++ b/tests/userfaultfd/userfaultfd.c
>> @@ -19,7 +19,7 @@ int page_size;
>>
>> void *fault_handler_thread(void *arg)
>> {
>> - long uffd = (long)arg;
>> + int uffd = (int)(intptr_t)arg;
>> struct uffd_msg msg = {0};
>> struct uffdio_copy uffdio_copy = {0};
>> ssize_t nread;
>> @@ -83,6 +83,16 @@ void *fault_handler_thread(void *arg)
>> }
>> }
>>
>> +int syscall_userfaultfd(int flags)
>> +{
>> +#ifdef __NR_userfaultfd
>> + return (int)syscall(__NR_userfaultfd, flags);
>> +#else
>> + errno = ENOSYS;
>> + return -1;
>> +#endif
>> +}
>> +
>> int main (int argc, char *argv[])
>> {
>> char *addr;
>> @@ -92,7 +102,7 @@ int main (int argc, char *argv[])
>> pthread_t thr; // ID of thread that handles page faults
>> ssize_t ret;
>>
>> - long uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
>> + int uffd = syscall_userfaultfd(O_CLOEXEC | O_NONBLOCK);
>> if (uffd < 0) {
>> if (errno == ENOSYS) {
>> return 8;
>> @@ -159,7 +169,8 @@ int main (int argc, char *argv[])
>> }
>>
>> // Create a thread that will process the userfaultfd events
>> - ret = pthread_create(&thr, NULL, fault_handler_thread, (void *) uffd);
>> + ret = pthread_create(&thr, NULL, fault_handler_thread,
>> + (void *)(intptr_t)uffd);
>> if (ret != 0) {
>> errno = ret;
>> perror("pthread_create");
>> --
>> 2.30.2
>>
--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.
