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

[Axel Rasmussen <axelrasmussen@google.com>]

On Wed, Jan 19, 2022 at 2:11 PM Lokesh Gidra <lokeshgidra@google.com> wrote:
>
> On Wed, Jan 19, 2022 at 2:03 PM Axel Rasmussen <axelrasmussen@google.com> wrote:
> >
> > On Wed, Jan 19, 2022 at 1:19 PM Suren Baghdasaryan <surenb@google.com> wrote:
> > >
> > > On Wed, Jan 19, 2022 at 12:39 PM Axel Rasmussen
> > > <axelrasmussen@google.com> 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@redhat.com/
>
> 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@intel.com> 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@intel.com/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@intel.com>
> > > > >
> > > > > 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@lists.01.org
> > > >
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