Re: [ammarfaizi2-block:google/android/kernel/common/android12-5.4 6517/9999] fs/userfaultfd.c:1519:9: warning: variable 'ioctls_out' set but not used

From: Lokesh Gidra
Date: Thu Jan 20 2022 - 13:16:40 EST

Thanks a lot for confirming. I hope I have not screwed up like this
anywhere else.

On Thu, Jan 20, 2022 at 10:15 AM Axel Rasmussen
<axelrasmussen@xxxxxxxxxx> wrote:
>
> On Wed, Jan 19, 2022 at 2:11 PM Lokesh Gidra <lokeshgidra@xxxxxxxxxx> wrote:
> >
> > On Wed, Jan 19, 2022 at 2:03 PM Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote:
> > >
> > > On Wed, Jan 19, 2022 at 1:19 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> > > >
> > > > On Wed, Jan 19, 2022 at 12:39 PM Axel Rasmussen
> > > > <axelrasmussen@xxxxxxxxxx> wrote:
> > > > >
> > > > > Lokesh, I only spent a few moments looking, but my suspicion is that
> > > > > this is the result of an incomplete backport of these patches to the
> > > > > Android kernel?
> > > > >
> > > > > The UFFDIO_CONTINUE patches introduced ioctls_out since the
> > > > > computation of it got more complicated, and those same patches also
> > > > > modified the put_user() on line 1533 here to use ioctls_out. I think
> > > > > Android backported the first part, but left out the second?
> > > >
> > > > The backport https://android-review.googlesource.com/c/kernel/common/+/1652718
> > > > looks like a mixture of
> > > > 14819305e09fe4 ("userfaultfd: wp: declare _UFFDIO_WRITEPROTECT
> > > > conditionally") and f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE
> > > > ioctl").
> > > > Not sure why it was done this way, maybe to minimize code changes
> > > > while backporting.
> > > > Simplest fix is probably to add __maybe_unused to ioctls_out declaration.
> > >
> > > Unfortunately, that doesn't quite do it. That would fix the warning,
> > > but the code in the original e-mail is still wrong: we incorrectly
> > > don't report the _UFFDIO_CONTINUE bit, unless we use the value we
> > > computed in ioctls_out.
> >
> > Apologies for the screw up. Actually, since 5.4 kernel didn't already
> > have UFFD_WRITE_PROTECT feature and neither was I interested in it, so
> > I attempted to only backport UFFDIO_CONTINUE feature and there
> > mistakenly missed this one out.
> >
> > Axel, wouldn't doing what Peter did in the following patch the right
> > thing to do?
> > https://lore.kernel.org/lkml/20200220163112.11409-18-peterx@xxxxxxxxxx/
> >
> > Basically:
> >
> > - if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
> > - UFFD_API_RANGE_IOCTLS,
> > - &user_uffdio_register->ioctls))
> > + if (put_user(ioctls_out, &user_uffdio_register->ioctls))
>
> Exactly right, that's the solution. And, I believe Kalesh has now
> applied exactly that to the Android tree here:
> https://android-review.googlesource.com/c/kernel/common/+/1955138 - so
> once that's merged, we can consider this fixed.
>
> >
> >
> > >
> > > >
> > > > >
> > > > > On Sun, Jan 16, 2022 at 10:11 AM kernel test robot <lkp@xxxxxxxxx> wrote:
> > > > > >
> > > > > > Hi Axel,
> > > > > >
> > > > > > FYI, the error/warning still remains.
> > > > > >
> > > > > > tree: https://github.com/ammarfaizi2/linux-block google/android/kernel/common/android12-5.4
> > > > > > head: bdf17ba628090156b539b1474eb5c636eeaf571b
> > > > > > commit: b69f713e60d03ae448e5c9fd92e5b0b193dea7be [6517/9999] BACKPORT: FROMGIT: userfaultfd: add UFFDIO_CONTINUE ioctl
> > > > > > config: x86_64-randconfig-a012 (https://download.01.org/0day-ci/archive/20220117/202201170247.Cir3moOM-lkp@xxxxxxxxx/config)
> > > > > > compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project c63a3175c2947e8c1a2d3bbe16a8586600705c54)
> > > > > > reproduce (this is a W=1 build):
> > > > > > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > > > > chmod +x ~/bin/make.cross
> > > > > > # https://github.com/ammarfaizi2/linux-block/commit/b69f713e60d03ae448e5c9fd92e5b0b193dea7be
> > > > > > git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block
> > > > > > git fetch --no-tags ammarfaizi2-block google/android/kernel/common/android12-5.4
> > > > > > git checkout b69f713e60d03ae448e5c9fd92e5b0b193dea7be
> > > > > > # save the config file to linux build tree
> > > > > > mkdir build_dir
> > > > > > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
> > > > > >
> > > > > > If you fix the issue, kindly add following tag as appropriate
> > > > > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > > > >
> > > > > > All warnings (new ones prefixed by >>):
> > > > > >
> > > > > > >> fs/userfaultfd.c:1519:9: warning: variable 'ioctls_out' set but not used [-Wunused-but-set-variable]
> > > > > > __u64 ioctls_out;
> > > > > > ^
> > > > > > 1 warning generated.
> > > > > >
> > > > > >
> > > > > > vim +/ioctls_out +1519 fs/userfaultfd.c
> > > > > >
> > > > > > 1311
> > > > > > 1312 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > > > > > 1313 unsigned long arg)
> > > > > > 1314 {
> > > > > > 1315 struct mm_struct *mm = ctx->mm;
> > > > > > 1316 struct vm_area_struct *vma, *prev, *cur;
> > > > > > 1317 int ret;
> > > > > > 1318 struct uffdio_register uffdio_register;
> > > > > > 1319 struct uffdio_register __user *user_uffdio_register;
> > > > > > 1320 unsigned long vm_flags, new_flags;
> > > > > > 1321 bool found;
> > > > > > 1322 bool basic_ioctls;
> > > > > > 1323 unsigned long start, end, vma_end;
> > > > > > 1324
> > > > > > 1325 user_uffdio_register = (struct uffdio_register __user *) arg;
> > > > > > 1326
> > > > > > 1327 ret = -EFAULT;
> > > > > > 1328 if (copy_from_user(&uffdio_register, user_uffdio_register,
> > > > > > 1329 sizeof(uffdio_register)-sizeof(__u64)))
> > > > > > 1330 goto out;
> > > > > > 1331
> > > > > > 1332 ret = -EINVAL;
> > > > > > 1333 if (!uffdio_register.mode)
> > > > > > 1334 goto out;
> > > > > > 1335 if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
> > > > > > 1336 goto out;
> > > > > > 1337 vm_flags = 0;
> > > > > > 1338 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
> > > > > > 1339 vm_flags |= VM_UFFD_MISSING;
> > > > > > 1340 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
> > > > > > 1341 vm_flags |= VM_UFFD_WP;
> > > > > > 1342 /*
> > > > > > 1343 * FIXME: remove the below error constraint by
> > > > > > 1344 * implementing the wprotect tracking mode.
> > > > > > 1345 */
> > > > > > 1346 ret = -EINVAL;
> > > > > > 1347 goto out;
> > > > > > 1348 }
> > > > > > 1349 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
> > > > > > 1350 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
> > > > > > 1351 goto out;
> > > > > > 1352 #endif
> > > > > > 1353 vm_flags |= VM_UFFD_MINOR;
> > > > > > 1354 }
> > > > > > 1355
> > > > > > 1356 ret = validate_range(mm, &uffdio_register.range.start,
> > > > > > 1357 uffdio_register.range.len);
> > > > > > 1358 if (ret)
> > > > > > 1359 goto out;
> > > > > > 1360
> > > > > > 1361 start = uffdio_register.range.start;
> > > > > > 1362 end = start + uffdio_register.range.len;
> > > > > > 1363
> > > > > > 1364 ret = -ENOMEM;
> > > > > > 1365 if (!mmget_not_zero(mm))
> > > > > > 1366 goto out;
> > > > > > 1367
> > > > > > 1368 down_write(&mm->mmap_sem);
> > > > > > 1369 if (!mmget_still_valid(mm))
> > > > > > 1370 goto out_unlock;
> > > > > > 1371 vma = find_vma_prev(mm, start, &prev);
> > > > > > 1372 if (!vma)
> > > > > > 1373 goto out_unlock;
> > > > > > 1374
> > > > > > 1375 /* check that there's at least one vma in the range */
> > > > > > 1376 ret = -EINVAL;
> > > > > > 1377 if (vma->vm_start >= end)
> > > > > > 1378 goto out_unlock;
> > > > > > 1379
> > > > > > 1380 /*
> > > > > > 1381 * If the first vma contains huge pages, make sure start address
> > > > > > 1382 * is aligned to huge page size.
> > > > > > 1383 */
> > > > > > 1384 if (is_vm_hugetlb_page(vma)) {
> > > > > > 1385 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
> > > > > > 1386
> > > > > > 1387 if (start & (vma_hpagesize - 1))
> > > > > > 1388 goto out_unlock;
> > > > > > 1389 }
> > > > > > 1390
> > > > > > 1391 /*
> > > > > > 1392 * Search for not compatible vmas.
> > > > > > 1393 */
> > > > > > 1394 found = false;
> > > > > > 1395 basic_ioctls = false;
> > > > > > 1396 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
> > > > > > 1397 cond_resched();
> > > > > > 1398
> > > > > > 1399 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
> > > > > > 1400 !!(cur->vm_flags & __VM_UFFD_FLAGS));
> > > > > > 1401
> > > > > > 1402 /* check not compatible vmas */
> > > > > > 1403 ret = -EINVAL;
> > > > > > 1404 if (!vma_can_userfault(cur, vm_flags))
> > > > > > 1405 goto out_unlock;
> > > > > > 1406
> > > > > > 1407 /*
> > > > > > 1408 * UFFDIO_COPY will fill file holes even without
> > > > > > 1409 * PROT_WRITE. This check enforces that if this is a
> > > > > > 1410 * MAP_SHARED, the process has write permission to the backing
> > > > > > 1411 * file. If VM_MAYWRITE is set it also enforces that on a
> > > > > > 1412 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
> > > > > > 1413 * F_WRITE_SEAL can be taken until the vma is destroyed.
> > > > > > 1414 */
> > > > > > 1415 ret = -EPERM;
> > > > > > 1416 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
> > > > > > 1417 goto out_unlock;
> > > > > > 1418
> > > > > > 1419 /*
> > > > > > 1420 * If this vma contains ending address, and huge pages
> > > > > > 1421 * check alignment.
> > > > > > 1422 */
> > > > > > 1423 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
> > > > > > 1424 end > cur->vm_start) {
> > > > > > 1425 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
> > > > > > 1426
> > > > > > 1427 ret = -EINVAL;
> > > > > > 1428
> > > > > > 1429 if (end & (vma_hpagesize - 1))
> > > > > > 1430 goto out_unlock;
> > > > > > 1431 }
> > > > > > 1432
> > > > > > 1433 /*
> > > > > > 1434 * Check that this vma isn't already owned by a
> > > > > > 1435 * different userfaultfd. We can't allow more than one
> > > > > > 1436 * userfaultfd to own a single vma simultaneously or we
> > > > > > 1437 * wouldn't know which one to deliver the userfaults to.
> > > > > > 1438 */
> > > > > > 1439 ret = -EBUSY;
> > > > > > 1440 if (cur->vm_userfaultfd_ctx.ctx &&
> > > > > > 1441 cur->vm_userfaultfd_ctx.ctx != ctx)
> > > > > > 1442 goto out_unlock;
> > > > > > 1443
> > > > > > 1444 /*
> > > > > > 1445 * Note vmas containing huge pages
> > > > > > 1446 */
> > > > > > 1447 if (is_vm_hugetlb_page(cur))
> > > > > > 1448 basic_ioctls = true;
> > > > > > 1449
> > > > > > 1450 found = true;
> > > > > > 1451 }
> > > > > > 1452 BUG_ON(!found);
> > > > > > 1453
> > > > > > 1454 if (vma->vm_start < start)
> > > > > > 1455 prev = vma;
> > > > > > 1456
> > > > > > 1457 ret = 0;
> > > > > > 1458 do {
> > > > > > 1459 cond_resched();
> > > > > > 1460
> > > > > > 1461 BUG_ON(!vma_can_userfault(vma, vm_flags));
> > > > > > 1462 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
> > > > > > 1463 vma->vm_userfaultfd_ctx.ctx != ctx);
> > > > > > 1464 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
> > > > > > 1465
> > > > > > 1466 /*
> > > > > > 1467 * Nothing to do: this vma is already registered into this
> > > > > > 1468 * userfaultfd and with the right tracking mode too.
> > > > > > 1469 */
> > > > > > 1470 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
> > > > > > 1471 (vma->vm_flags & vm_flags) == vm_flags)
> > > > > > 1472 goto skip;
> > > > > > 1473
> > > > > > 1474 if (vma->vm_start > start)
> > > > > > 1475 start = vma->vm_start;
> > > > > > 1476 vma_end = min(end, vma->vm_end);
> > > > > > 1477
> > > > > > 1478 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
> > > > > > 1479 prev = vma_merge(mm, prev, start, vma_end, new_flags,
> > > > > > 1480 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
> > > > > > 1481 vma_policy(vma),
> > > > > > 1482 ((struct vm_userfaultfd_ctx){ ctx }),
> > > > > > 1483 vma_get_anon_name(vma));
> > > > > > 1484 if (prev) {
> > > > > > 1485 vma = prev;
> > > > > > 1486 goto next;
> > > > > > 1487 }
> > > > > > 1488 if (vma->vm_start < start) {
> > > > > > 1489 ret = split_vma(mm, vma, start, 1);
> > > > > > 1490 if (ret)
> > > > > > 1491 break;
> > > > > > 1492 }
> > > > > > 1493 if (vma->vm_end > end) {
> > > > > > 1494 ret = split_vma(mm, vma, end, 0);
> > > > > > 1495 if (ret)
> > > > > > 1496 break;
> > > > > > 1497 }
> > > > > > 1498 next:
> > > > > > 1499 /*
> > > > > > 1500 * In the vma_merge() successful mprotect-like case 8:
> > > > > > 1501 * the next vma was merged into the current one and
> > > > > > 1502 * the current one has not been updated yet.
> > > > > > 1503 */
> > > > > > 1504 vma->vm_flags = new_flags;
> > > > > > 1505 vma->vm_userfaultfd_ctx.ctx = ctx;
> > > > > > 1506
> > > > > > 1507 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
> > > > > > 1508 hugetlb_unshare_all_pmds(vma);
> > > > > > 1509
> > > > > > 1510 skip:
> > > > > > 1511 prev = vma;
> > > > > > 1512 start = vma->vm_end;
> > > > > > 1513 vma = vma->vm_next;
> > > > > > 1514 } while (vma && vma->vm_start < end);
> > > > > > 1515 out_unlock:
> > > > > > 1516 up_write(&mm->mmap_sem);
> > > > > > 1517 mmput(mm);
> > > > > > 1518 if (!ret) {
> > > > > > > 1519 __u64 ioctls_out;
> > > > > > 1520
> > > > > > 1521 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
> > > > > > 1522 UFFD_API_RANGE_IOCTLS;
> > > > > > 1523
> > > > > > 1524 /* CONTINUE ioctl is only supported for MINOR ranges. */
> > > > > > 1525 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
> > > > > > 1526 ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
> > > > > > 1527
> > > > > > 1528 /*
> > > > > > 1529 * Now that we scanned all vmas we can already tell
> > > > > > 1530 * userland which ioctls methods are guaranteed to
> > > > > > 1531 * succeed on this range.
> > > > > > 1532 */
> > > > > > 1533 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
> > > > > > 1534 UFFD_API_RANGE_IOCTLS,
> > > > > > 1535 &user_uffdio_register->ioctls))
> > > > > > 1536 ret = -EFAULT;
> > > > > > 1537 }
> > > > > > 1538 out:
> > > > > > 1539 return ret;
> > > > > > 1540 }
> > > > > > 1541
> > > > > >
> > > > > > ---
> > > > > > 0-DAY CI Kernel Test Service, Intel Corporation
> > > > > > https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx
> > > > >