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Message-ID: <20171113151641.yfqrecpcxllpn5mq@dhcp22.suse.cz>
Date: Mon, 13 Nov 2017 16:16:41 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Michael Ellerman <mpe@...erman.id.au>
Cc: Joel Stanley <joel@....id.au>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux-Next Mailing List <linux-next@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Russell King <linux@...linux.org.uk>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
Ralf Baechle <ralf@...ux-mips.org>,
"James E.J. Bottomley" <jejb@...isc-linux.org>,
Helge Deller <deller@....de>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Rich Felker <dalias@...c.org>,
"David S. Miller" <davem@...emloft.net>,
Chris Zankel <chris@...kel.net>,
Max Filippov <jcmvbkbc@...il.com>,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, linux-mips@...ux-mips.org,
linux-parisc@...r.kernel.org, linux-sh@...r.kernel.org,
sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org
Subject: Re: linux-next: Tree for Nov 7
On Mon 13-11-17 13:00:57, Michal Hocko wrote:
[...]
> Yes, I have mentioned that in the previous email but the amount of code
> would be even larger. Basically every arch which reimplements
> arch_get_unmapped_area would have to special case new MAP_FIXED flag to
> do vma lookup.
It turned out that this might be much more easier than I thought after
all. It seems we can really handle that in the common code. This would
mean that we are exposing a new functionality to the userspace though.
Myabe this would be useful on its own though. Just a quick draft (not
even compile tested) whether this makes sense in general. I would be
worried about unexpected behavior when somebody set other bit without a
good reason and we might fail with ENOMEM for such a call now.
Elf loader would then use MAP_FIXED_SAFE rather than MAP_FIXED.
---
diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
index 3b26cc62dadb..d021c21f9b01 100644
--- a/arch/alpha/include/uapi/asm/mman.h
+++ b/arch/alpha/include/uapi/asm/mman.h
@@ -31,6 +31,9 @@
#define MAP_STACK 0x80000 /* give out an address that is best suited for process/thread stacks */
#define MAP_HUGETLB 0x100000 /* create a huge page mapping */
+#define MAP_KEEP_MAPPING 0x2000000
+#define MAP_FIXED_SAFE MAP_FIXED|MAP_KEEP_MAPPING /* enforce MAP_FIXED without clobbering an existing mapping */
+
#define MS_ASYNC 1 /* sync memory asynchronously */
#define MS_SYNC 2 /* synchronous memory sync */
#define MS_INVALIDATE 4 /* invalidate the caches */
diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
index da3216007fe0..51e3885fbfc1 100644
--- a/arch/mips/include/uapi/asm/mman.h
+++ b/arch/mips/include/uapi/asm/mman.h
@@ -49,6 +49,9 @@
#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_KEEP_MAPPING 0x2000000
+#define MAP_FIXED_SAFE MAP_FIXED|MAP_KEEP_MAPPING /* enforce MAP_FIXED without clobbering an existing mapping */
+
/*
* Flags for msync
*/
diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index cc9ba1d34779..5a4381484fc5 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -25,6 +25,9 @@
#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_KEEP_MAPPING 0x2000000
+#define MAP_FIXED_SAFE MAP_FIXED|MAP_KEEP_MAPPING /* enforce MAP_FIXED without clobbering an existing mapping */
+
#define MS_SYNC 1 /* synchronous memory sync */
#define MS_ASYNC 2 /* sync memory asynchronously */
#define MS_INVALIDATE 4 /* invalidate the caches */
diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
index b15b278aa314..5df8a81524da 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -62,6 +62,9 @@
# define MAP_UNINITIALIZED 0x0 /* Don't support this flag */
#endif
+#define MAP_KEEP_MAPPING 0x2000000
+#define MAP_FIXED_SAFE MAP_FIXED|MAP_KEEP_MAPPING /* enforce MAP_FIXED without clobbering an existing mapping */
+
/*
* Flags for msync
*/
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 203268f9231e..22442846f5c8 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -25,6 +25,9 @@
# define MAP_UNINITIALIZED 0x0 /* Don't support this flag */
#endif
+#define MAP_KEEP_MAPPING 0x2000000
+#define MAP_FIXED_SAFE MAP_FIXED|MAP_KEEP_MAPPING /* enforce MAP_FIXED without clobbering an existing mapping */
+
/*
* Flags for mlock
*/
diff --git a/mm/mmap.c b/mm/mmap.c
index 680506faceae..e53b6b15a8d9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1365,6 +1365,13 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (offset_in_page(addr))
return addr;
+ if ((flags & MAP_FIXED_SAFE) == MAP_FIXED_SAFE) {
+ struct vm_area_struct *vma = find_vma(mm, addr);
+
+ if (vma && vma->vm_start <= addr)
+ return -ENOMEM;
+ }
+
if (prot == PROT_EXEC) {
pkey = execute_only_pkey(mm);
if (pkey < 0)
--
Michal Hocko
SUSE Labs
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