mm: add arch hook to validate mmap() prot flags

Add a hook to permit architectures to perform validation on the prot
flags passed to mmap(), like arch_validate_prot() does for mprotect().
This will be used by arm64 to reject PROT_WRITE+PROT_EXEC mappings on
configurations that run with WXN enabled.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-87-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/include/linux/mman.h b/include/linux/mman.h
index dc7048824be81d628ca12f0874c1a7508da0d5c1..ec5e7f606e434f943c564442a48d2907baee36ed 100644 (file)
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -124,6 +124,21 @@ static inline bool arch_validate_flags(unsigned long flags)
 #define arch_validate_flags arch_validate_flags
 #endif
 
+#ifndef arch_validate_mmap_prot
+/*
+ * This is called from mmap(), which ignores unknown prot bits so the default
+ * is to accept anything.
+ *
+ * Returns true if the prot flags are valid
+ */
+static inline bool arch_validate_mmap_prot(unsigned long prot,
+                                          unsigned long addr)
+{
+       return true;
+}
+#define arch_validate_mmap_prot arch_validate_mmap_prot
+#endif
+
 /*
  * Optimisation macro.  It is equivalent to:
  *      (x & bit1) ? bit2 : 0

diff --git a/mm/mmap.c b/mm/mmap.c
index d89770eaab6b6111117783ca7ff532871c1d71a5..977a8c3fd9f5f80e901b56fef4b19baabb7c7907 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1229,6 +1229,9 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
                if (!(file && path_noexec(&file->f_path)))
                        prot |= PROT_EXEC;
 
+       if (!arch_validate_mmap_prot(prot, addr))
+               return -EACCES;
+
        /* force arch specific MAP_FIXED handling in get_unmapped_area */
        if (flags & MAP_FIXED_NOREPLACE)
                flags |= MAP_FIXED;