linux-kernel - [PATCH 1/3] mm: fix the MAP

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Message-Id: <20190703122359.18200-2-hch@lst.de>
Date:   Wed,  3 Jul 2019 05:23:57 -0700
From:   Christoph Hellwig <hch@....de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-riscv@...ts.infradead.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Vladimir Murzin <vladimir.murzin@....com>
Subject: [PATCH 1/3] mm: fix the MAP_UNINITIALIZED flag

We can't expose UAPI symbols differently based on CONFIG_ symbols, as
userspace won't have them available.  Instead always define the flag,
but only respect it based on the config option.

Signed-off-by: Christoph Hellwig <hch@....de>
Reviewed-by: Vladimir Murzin <vladimir.murzin@....com>
---
 arch/xtensa/include/uapi/asm/mman.h    | 6 +-----
 include/uapi/asm-generic/mman-common.h | 8 +++-----
 mm/nommu.c                             | 4 +++-
 3 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
index be726062412b..ebbb48842190 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -56,12 +56,8 @@
 #define MAP_STACK	0x40000		/* give out an address that is best suited for process/thread stacks */
 #define MAP_HUGETLB	0x80000		/* create a huge page mapping */
 #define MAP_FIXED_NOREPLACE 0x100000	/* MAP_FIXED which doesn't unmap underlying mapping */
-#ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED
-# define MAP_UNINITIALIZED 0x4000000	/* For anonymous mmap, memory could be
+#define MAP_UNINITIALIZED 0x4000000	/* For anonymous mmap, memory could be
 					 * uninitialized */
-#else
-# define MAP_UNINITIALIZED 0x0		/* Don't support this flag */
-#endif
 
 /*
  * Flags for msync
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index abd238d0f7a4..cb556b430e71 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -19,15 +19,13 @@
 #define MAP_TYPE	0x0f		/* Mask for type of mapping */
 #define MAP_FIXED	0x10		/* Interpret addr exactly */
 #define MAP_ANONYMOUS	0x20		/* don't use a file */
-#ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED
-# define MAP_UNINITIALIZED 0x4000000	/* For anonymous mmap, memory could be uninitialized */
-#else
-# define MAP_UNINITIALIZED 0x0		/* Don't support this flag */
-#endif
 
 /* 0x0100 - 0x80000 flags are defined in asm-generic/mman.h */
 #define MAP_FIXED_NOREPLACE	0x100000	/* MAP_FIXED which doesn't unmap underlying mapping */
 
+#define MAP_UNINITIALIZED 0x4000000	/* For anonymous mmap, memory could be
+					 * uninitialized */
+
 /*
  * Flags for mlock
  */
diff --git a/mm/nommu.c b/mm/nommu.c
index d8c02fbe03b5..ec75a0dffd4f 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1349,7 +1349,9 @@ unsigned long do_mmap(struct file *file,
 	add_nommu_region(region);
 
 	/* clear anonymous mappings that don't ask for uninitialized data */
-	if (!vma->vm_file && !(flags & MAP_UNINITIALIZED))
+	if (!vma->vm_file &&
+	    (!IS_ENABLED(CONFIG_MMAP_ALLOW_UNINITIALIZED) ||
+	     !(flags & MAP_UNINITIALIZED)))
 		memset((void *)region->vm_start, 0,
 		       region->vm_end - region->vm_start);
 
-- 
2.20.1