+ drivers-misc-open-dice-dont-touch-vm_mayshare.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: drivers/misc/open-dice: don't touch VM_MAYSHARE
has been added to the -mm mm-unstable branch.  Its filename is
     drivers-misc-open-dice-dont-touch-vm_mayshare.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/drivers-misc-open-dice-dont-touch-vm_mayshare.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: drivers/misc/open-dice: don't touch VM_MAYSHARE
Date: Mon, 2 Jan 2023 17:08:56 +0100

A MAP_SHARED mapping always has VM_MAYSHARE set, and writable
(VM_MAYWRITE) MAP_SHARED mappings have VM_SHARED set as well.  To identify
a MAP_SHARED mapping, it's sufficient to look at VM_MAYSHARE.

We cannot have VM_MAYSHARE|VM_WRITE mappings without having VM_SHARED set.
Consequently, current code will never actually end up clearing
VM_MAYSHARE and that code is confusing, because nobody is supposed to mess
with VM_MAYWRITE.

Let's clean it up and restructure the code. No functional change intended.

Link: https://lkml.kernel.org/r/20230102160856.500584-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/misc/open-dice.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

--- a/drivers/misc/open-dice.c~drivers-misc-open-dice-dont-touch-vm_mayshare
+++ a/drivers/misc/open-dice.c
@@ -90,15 +90,13 @@ static int open_dice_mmap(struct file *f
 {
 	struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);
 
-	/* Do not allow userspace to modify the underlying data. */
-	if ((vma->vm_flags & VM_WRITE) && (vma->vm_flags & VM_SHARED))
-		return -EPERM;
-
-	/* Ensure userspace cannot acquire VM_WRITE + VM_SHARED later. */
-	if (vma->vm_flags & VM_WRITE)
-		vma->vm_flags &= ~VM_MAYSHARE;
-	else if (vma->vm_flags & VM_SHARED)
+	if (vma->vm_flags & VM_MAYSHARE) {
+		/* Do not allow userspace to modify the underlying data. */
+		if (vma->vm_flags & VM_WRITE)
+			return -EPERM;
+		/* Ensure userspace cannot acquire VM_WRITE later. */
 		vma->vm_flags &= ~VM_MAYWRITE;
+	}
 
 	/* Create write-combine mapping so all clients observe a wipe. */
 	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
_

Patches currently in -mm which might be from david@redhat.com are

mm-hugetlb-fix-pte-marker-handling-in-hugetlb_change_protection.patch
mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection.patch
mm-userfaultfd-enable-writenotify-while-userfaultfd-wp-is-enabled-for-a-vma.patch
mm-userfaultfd-rely-on-vma-vm_page_prot-in-uffd_wp_range.patch
mm-userfaultfd-rely-on-vma-vm_page_prot-in-uffd_wp_range-fix.patch
mm-mprotect-drop-pgprot_t-parameter-from-change_protection.patch
mm-mprotect-drop-pgprot_t-parameter-from-change_protection-fix.patch
selftests-vm-cow-add-cow-tests-for-collapsing-of-pte-mapped-anon-thp.patch
mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping.patch
mm-nommu-dont-use-vm_mayshare-for-map_private-mappings.patch
drivers-misc-open-dice-dont-touch-vm_mayshare.patch