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From: Michal Hocko <mhocko@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Joel Stanley <joel@jms.id.au>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	"James E.J. Bottomley" <jejb@parisc-linux.org>,
	Helge Deller <deller@gmx.de>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	"David S. Miller" <davem@davemloft.net>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-mips@linux-mips.org
Subject: Re: linux-next: Tree for Nov 7
Date: Mon, 13 Nov 2017 16:16:41 +0100
Message-ID: <20171113151641.yfqrecpcxllpn5mq@dhcp22.suse.cz> (raw)
In-Reply-To: <20171113120057.555mvrs4fjq5tyng@dhcp22.suse.cz>

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

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-07  5:22 Stephen Rothwell
2017-11-07 22:22 ` Joel Stanley
2017-11-08 14:20   ` Michal Hocko
2017-11-10 12:30     ` Michal Hocko
2017-11-12  1:08       ` Joel Stanley
2017-11-13  9:20         ` Michal Hocko
2017-11-13  9:34           ` Russell King - ARM Linux
2017-11-13  9:42           ` Michal Hocko
2017-11-13 11:34             ` Michael Ellerman
2017-11-13 12:00               ` Michal Hocko
2017-11-13 15:16                 ` Michal Hocko [this message]
2017-11-13 15:48                   ` Russell King - ARM Linux
2017-11-13 15:59                     ` Michal Hocko
2017-11-13 15:49                   ` Michal Hocko
2017-11-13 16:06                     ` Michal Hocko
2017-11-13 16:35                       ` Khalid Aziz
2017-11-14  7:07                         ` Michal Hocko
2017-11-14  9:18                       ` Michael Ellerman
2017-11-14  9:29                         ` Michal Hocko
2017-11-14  9:02                   ` Michael Ellerman
2017-11-14  8:54                 ` Michael Ellerman
2017-11-14  9:04                   ` Michal Hocko
2017-11-14 14:52                     ` Khalid Aziz
2017-11-13 14:11           ` Michal Hocko
2017-11-13 15:09             ` Russell King - ARM Linux
2017-11-13 15:31               ` Michal Hocko
2017-11-14  0:03         ` Andrew Morton
2017-11-14  0:36           ` Stephen Rothwell
  -- strict thread matches above, loose matches on Subject: below --
2019-11-07  8:07 Stephen Rothwell
2018-11-07  3:16 Stephen Rothwell
2013-11-07  7:31 Stephen Rothwell
2012-11-07  5:15 Stephen Rothwell

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