[PATCH v3 13/23] mm: Introduce arch_validate_flags()

Catalin Marinas
2020-04-21T14:26:35Z

Similarly to arch_validate_prot() called from do_mprotect_pkey(), an
architecture may need to sanity-check the new vm_flags.

Define a dummy function always returning true. In addition to
do_mprotect_pkey(), also invoke it from mmap_region() prior to updating
vma->vm_page_prot to allow the architecture code to veto potentially
inconsistent vm_flags.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---

Notes:
v2:
- Some comments updated.

include/linux/mman.h | 13 +++++++++++++
mm/mmap.c | 9 +++++++++
mm/mprotect.c | 6 ++++++
3 files changed, 28 insertions(+)

diff --git a/include/linux/mman.h b/include/linux/mman.h
index 15c1162b9d65..09dd414b81b6 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -103,6 +103,19 @@ static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
#define arch_validate_prot arch_validate_prot
#endif

+#ifndef arch_validate_flags
+/*
+ * This is called from mmap() and mprotect() with the updated vma->vm_flags.
+ *
+ * Returns true if the VM_* flags are valid.
+ */
+static inline bool arch_validate_flags(unsigned long flags)
+{
+ return true;
+}
+#define arch_validate_flags arch_validate_flags
+#endif
+
/*
* Optimisation macro. It is equivalent to:
* (x & bit1) ? bit2 : 0
diff --git a/mm/mmap.c b/mm/mmap.c
index f609e9ec4a25..d5fc93c2072e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1792,6 +1792,15 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
vma_set_anonymous(vma);
}

+ /* Allow architectures to sanity-check the vm_flags */
+ if (!arch_validate_flags(vma->vm_flags)) {
+ error = -EINVAL;
+ if (file)
+ goto unmap_and_free_vma;
+ else
+ goto free_vma;
+ }
+
vma_link(mm, vma, prev, rb_link, rb_parent);
/* Once vma denies write, undo our temporary denial count */
if (file) {
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 494192ca954b..04b1d2cf0e74 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -603,6 +603,12 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
goto out;
}

+ /* Allow architectures to sanity-check the new flags */
+ if (!arch_validate_flags(newflags)) {
+ error = -EINVAL;
+ goto out;
+ }
+
error = security_file_mprotect(vma, reqprot, prot);
if (error)
goto out;