linux-kernel - [PATCH RFC 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap

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Message-Id: <20210423131640.20080-7-david@redhat.com>
Date:   Fri, 23 Apr 2021 15:16:39 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
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        x86@...nel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH RFC 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff()

Let's also remove masking off MAP_DENYWROTE from ksys_mmap_pgoff():
the last in-tree occurrence of MAP_DENYWRITE is now in LEGACY_MAP_MASK,
which accepts the flag e.g., for MAP_SHARED_VALIDATE; however, the flag
is ignored throughout the kernel now.

Add a comment to LEGACY_MAP_MASK stating that MAP_DENYWRITE is ignored.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/mman.h | 3 ++-
 mm/mmap.c            | 2 --
 mm/nommu.c           | 2 --
 3 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/include/linux/mman.h b/include/linux/mman.h
index bd9aadda047b..b66e91b8176c 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -32,7 +32,8 @@
  * The historical set of flags that all mmap implementations implicitly
  * support when a ->mmap_validate() op is not provided in file_operations.
  *
- * MAP_EXECUTABLE is completely ignored throughout the kernel.
+ * MAP_EXECUTABLE and MAP_DENYWRITE are completely ignored throughout the
+ * kernel.
  */
 #define LEGACY_MAP_MASK (MAP_SHARED \
 		| MAP_PRIVATE \
diff --git a/mm/mmap.c b/mm/mmap.c
index b335f8907568..33479ce05653 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1623,8 +1623,6 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
 			return PTR_ERR(file);
 	}
 
-	flags &= ~MAP_DENYWRITE;
-
 	retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
 out_fput:
 	if (file)
diff --git a/mm/nommu.c b/mm/nommu.c
index 1fafe3e9d3df..7d85c8a46582 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1306,8 +1306,6 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
 			goto out;
 	}
 
-	flags &= ~MAP_DENYWRITE;
-
 	retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
 
 	if (file)
-- 
2.30.2