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| author | Dmitry Safonov <dsafonov@virtuozzo.com> | 2017-03-06 17:17:19 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2017-03-13 14:59:22 +0100 |
| commit | 1b028f784e8c341e762c264f70dc0ca1418c8b7a (patch) | |
| tree | ef63f639dc3a8f1d95f8e485314e5d2ebfa6b8a4 /arch/Kconfig | |
| parent | 8f3e474f3cea7b2470218a6ed6da47ff02147dce (diff) | |
| download | lwn-1b028f784e8c341e762c264f70dc0ca1418c8b7a.tar.gz lwn-1b028f784e8c341e762c264f70dc0ca1418c8b7a.zip | |
x86/mm: Introduce mmap_compat_base() for 32-bit mmap()
mmap() uses a base address, from which it starts to look for a free space
for allocation.
The base address is stored in mm->mmap_base, which is calculated during
exec(). The address depends on task's size, set rlimit for stack, ASLR
randomization. The base depends on the task size and the number of random
bits which are different for 64-bit and 32bit applications.
Due to the fact, that the base address is fixed, its mmap() from a compat
(32bit) syscall issued by a 64bit task will return a address which is based
on the 64bit base address and does not fit into the 32bit address space
(4GB). The returned pointer is truncated to 32bit, which results in an
invalid address.
To solve store a seperate compat address base plus a compat legacy address
base in mm_struct. These bases are calculated at exec() time and can be
used later to address the 32bit compat mmap() issued by 64 bit
applications.
As a consequence of this change 32-bit applications issuing a 64-bit
syscall (after doing a long jump) will get a 64-bit mapping now. Before
this change 32-bit applications always got a 32bit mapping.
[ tglx: Massaged changelog and added a comment ]
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: 0x7f454c46@gmail.com
Cc: linux-mm@kvack.org
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20170306141721.9188-4-dsafonov@virtuozzo.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/Kconfig')
| -rw-r--r-- | arch/Kconfig | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index cd211a14a88f..c4d6833aacd9 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -700,6 +700,13 @@ config ARCH_MMAP_RND_COMPAT_BITS This value can be changed after boot using the /proc/sys/vm/mmap_rnd_compat_bits tunable +config HAVE_ARCH_COMPAT_MMAP_BASES + bool + help + This allows 64bit applications to invoke 32-bit mmap() syscall + and vice-versa 32-bit applications to call 64-bit mmap(). + Required for applications doing different bitness syscalls. + config HAVE_COPY_THREAD_TLS bool help |