linux-kernel - [PATCH 4/6] mm/userfaultfd: Fail uffd-wp registeration if not supported

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Message-Id: <20210428225030.9708-5-peterx@redhat.com>
Date:   Wed, 28 Apr 2021 18:50:28 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Mike Kravetz <mike.kravetz@...cle.com>, peterx@...hat.com,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jerome Glisse <jglisse@...hat.com>
Subject: [PATCH 4/6] mm/userfaultfd: Fail uffd-wp registeration if not supported

We should fail uffd-wp registration immediately if the arch does not even have
CONFIG_HAVE_ARCH_USERFAULTFD_WP defined.  That'll block also relevant ioctls on
e.g. UFFDIO_WRITEPROTECT because that'll check against VM_UFFD_WP, which can
only be applied with a success registration.

Remove the WP feature bit too for those archs when handling UFFDIO_API ioctl.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 fs/userfaultfd.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 14f92285d04f8..5dd78238cc156 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1304,8 +1304,12 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	vm_flags = 0;
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
 		vm_flags |= VM_UFFD_MISSING;
-	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
+	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+		goto out;
+#endif
 		vm_flags |= VM_UFFD_WP;
+	}
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
 		goto out;
@@ -1942,6 +1946,9 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 	uffdio_api.features = UFFD_API_FEATURES;
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
 	uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS;
+#endif
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+	uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
 #endif
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
-- 
2.26.2