+ mm-refactor-map_deny_write_exec.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm: refactor map_deny_write_exec()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-refactor-map_deny_write_exec.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-refactor-map_deny_write_exec.patch

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

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------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Subject: mm: refactor map_deny_write_exec()
Date: Wed, 23 Oct 2024 21:38:28 +0100

Refactor the map_deny_write_exec() to not unnecessarily require a VMA
parameter but rather to accept VMA flags parameters, which allows us to
use this function early in mmap_region() in a subsequent commit.

While we're here, we refactor the function to be more readable and add
some additional documentation.

Link: https://lkml.kernel.org/r/e82d23cebaa87fe5b767fecf9e730e0059066e63.1729715266.git.lorenzo.stoakes@oracle.com
Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: Jann Horn <jannh@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Jann Horn <jannh@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mman.h |   21 ++++++++++++++++++---
 mm/mmap.c            |    2 +-
 mm/mprotect.c        |    2 +-
 mm/vma.h             |    2 +-
 4 files changed, 21 insertions(+), 6 deletions(-)

--- a/include/linux/mman.h~mm-refactor-map_deny_write_exec
+++ a/include/linux/mman.h
@@ -188,16 +188,31 @@ static inline bool arch_memory_deny_writ
  *
  *	d)	mmap(PROT_READ | PROT_EXEC)
  *		mmap(PROT_READ | PROT_EXEC | PROT_BTI)
+ *
+ * This is only applicable if the user has set the Memory-Deny-Write-Execute
+ * (MDWE) protection mask for the current process.
+ *
+ * @old specifies the VMA flags the VMA originally possessed, and @new the ones
+ * we propose to set.
+ *
+ * Return: false if proposed change is OK, true if not ok and should be denied.
  */
-static inline bool map_deny_write_exec(struct vm_area_struct *vma,  unsigned long vm_flags)
+static inline bool map_deny_write_exec(unsigned long old, unsigned long new)
 {
+	/* If MDWE is disabled, we have nothing to deny. */
 	if (!test_bit(MMF_HAS_MDWE, &current->mm->flags))
 		return false;
 
-	if ((vm_flags & VM_EXEC) && (vm_flags & VM_WRITE))
+	/* If the new VMA is not executable, we have nothing to deny. */
+	if (!(new & VM_EXEC))
+		return false;
+
+	/* Under MDWE we do not accept newly writably executable VMAs... */
+	if (new & VM_WRITE)
 		return true;
 
-	if (!(vma->vm_flags & VM_EXEC) && (vm_flags & VM_EXEC))
+	/* ...nor previously non-executable VMAs becoming executable. */
+	if (!(old & VM_EXEC))
 		return true;
 
 	return false;
--- a/mm/mmap.c~mm-refactor-map_deny_write_exec
+++ a/mm/mmap.c
@@ -1504,7 +1504,7 @@ unsigned long mmap_region(struct file *f
 		vma_set_anonymous(vma);
 	}
 
-	if (map_deny_write_exec(vma, vma->vm_flags)) {
+	if (map_deny_write_exec(vma->vm_flags, vma->vm_flags)) {
 		error = -EACCES;
 		goto close_and_free_vma;
 	}
--- a/mm/mprotect.c~mm-refactor-map_deny_write_exec
+++ a/mm/mprotect.c
@@ -810,7 +810,7 @@ static int do_mprotect_pkey(unsigned lon
 			break;
 		}
 
-		if (map_deny_write_exec(vma, newflags)) {
+		if (map_deny_write_exec(vma->vm_flags, newflags)) {
 			error = -EACCES;
 			break;
 		}
--- a/mm/vma.h~mm-refactor-map_deny_write_exec
+++ a/mm/vma.h
@@ -42,7 +42,7 @@ struct vma_munmap_struct {
 	int vma_count;                  /* Number of vmas that will be removed */
 	bool unlock;                    /* Unlock after the munmap */
 	bool clear_ptes;                /* If there are outstanding PTE to be cleared */
-	/* 1 byte hole */
+	/* 2 byte hole */
 	unsigned long nr_pages;         /* Number of pages being removed */
 	unsigned long locked_vm;        /* Number of locked pages */
 	unsigned long nr_accounted;     /* Number of VM_ACCOUNT pages */
_

Patches currently in -mm which might be from lorenzo.stoakes@oracle.com are

fork-do-not-invoke-uffd-on-fork-if-error-occurs.patch
fork-only-invoke-khugepaged-ksm-hooks-if-no-error.patch
mm-vma-add-expand-only-vma-merge-mode-and-optimise-do_brk_flags.patch
tools-testing-add-expand-only-mode-vma-test.patch
mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook.patch
mm-unconditionally-close-vmas-on-error.patch
mm-refactor-map_deny_write_exec.patch
mm-resolve-faulty-mmap_region-error-path-behaviour.patch
tools-testing-add-additional-vma_internalh-stubs.patch
mm-isolate-mmap-internal-logic-to-mm-vmac.patch
mm-refactor-__mmap_region.patch
mm-defer-second-attempt-at-merge-on-mmap.patch
selftests-mm-add-pkey_sighandler_xx-hugetlb_dio-to-gitignore.patch
mm-refactor-mm_access-to-not-return-null.patch
mm-refactor-mm_access-to-not-return-null-fix.patch
mm-madvise-unrestrict-process_madvise-for-current-process.patch
maple_tree-do-not-hash-pointers-on-dump-in-debug-mode.patch
tools-testing-fix-phys_addr_t-size-on-64-bit-systems.patch