On 2/11/21 11:59 PM, Aneesh Kumar K.V wrote:
>
> Hi,
>
> I am trying to estabilish the behaviour we should expect when passing a
> buffer with memory keys attached to io_uring syscalls. As show in the
> blow test
>
> /*
> * gcc -Wall -O2 -D_GNU_SOURCE -o pkey_uring pkey_uring.c -luring
> */
> #include <stdio.h>
> #include <fcntl.h>
> #include <string.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <sys/mman.h>
> #include "liburing.h"
>
> #define PAGE_SIZE (64 << 10)
>
> int main(int argc, char *argv[])
> {
> int fd, ret, pkey;
> struct io_uring ring;
> struct io_uring_sqe *sqe;
> struct io_uring_cqe *cqe;
> struct iovec iovec;
> void *buf;
>
> if (argc < 2) {
> printf("%s: file\n", argv[0]);
> return 1;
> }
>
> ret = io_uring_queue_init(1, &ring, IORING_SETUP_SQPOLL);
> if (ret < 0) {
> fprintf(stderr, "queue_init: %s\n", strerror(-ret));
> return 1;
> }
>
> fd = open(argv[1], O_RDONLY | O_DIRECT);
> if (fd < 0) {
> perror("open");
> return 1;
> }
>
> if (posix_memalign(&buf, PAGE_SIZE, PAGE_SIZE))
> return 1;
> iovec.iov_base = buf;
> iovec.iov_len = PAGE_SIZE;
>
> //mprotect(buf, PAGE_SIZE, PROT_NONE);
> pkey = pkey_alloc(0, PKEY_DISABLE_WRITE);
> pkey_mprotect(buf, PAGE_SIZE, PROT_READ | PROT_WRITE, pkey);
>
>
> sqe = io_uring_get_sqe(&ring);
> if (!sqe) {
> perror("io_uring_get_sqe");
> return 1;
> }
> io_uring_prep_readv(sqe, fd, &iovec, 1, 0);
>
> ret = io_uring_submit(&ring);
> if (ret != 1) {
> fprintf(stderr, "io_uring_submit: %s\n", strerror(-ret));
> return 1;
> }
>
> ret = io_uring_wait_cqe(&ring, &cqe);
>
> if (cqe->res < 0)
> fprintf(stderr, "iouring submit failed %s\n",
> strerror(-cqe->res));
> else
> fprintf(stderr, "iouring submit success\n");
>
> io_uring_cqe_seen(&ring, cqe);
>
> /*
> * let's access this via a read syscall
> */
> ret = read(fd, buf, PAGE_SIZE);
> if (ret < 0)
> fprintf(stderr, "read failed : %s\n", strerror(errno));
>
> close(fd);
> io_uring_queue_exit(&ring);
>
> return 0;
> }
>
> A read syscall do fail with EFAULT. But we allow read via io_uring
> syscalls. Is that ok? Considering memory keys are thread-specific we
> could debate that kernel thread can be considered to be the one that got all
> access
> allowed via keys or we could update that access is denied via kernel
> thread for any key value other than default key (key 0). Other option
> is to inherit the memory key restrictions when doing
> io_uring_submit() and use the same when accessing the userspace from
> kernel thread.
>
> Any thoughts here with respect to what should be behaviour?
It this a powerpc thing? I get -EFAULT on x86 for both reads, io_uring
and regular syscall. That includes SQPOLL, not using SQPOLL, or
explicitly setting IOSQE_ASYNC on the sqe.
--
Jens Axboe
