From 1b028f784e8c341e762c264f70dc0ca1418c8b7a Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Mon, 6 Mar 2017 17:17:19 +0300 Subject: 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 Cc: 0x7f454c46@gmail.com Cc: linux-mm@kvack.org Cc: Andy Lutomirski Cc: Cyrill Gorcunov Cc: Borislav Petkov Cc: "Kirill A. Shutemov" Link: http://lkml.kernel.org/r/20170306141721.9188-4-dsafonov@virtuozzo.com Signed-off-by: Thomas Gleixner --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/x86/Kconfig') diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index cc98d5a294ee..2bab9d093b51 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -106,6 +106,7 @@ config X86 select HAVE_ARCH_KMEMCHECK select HAVE_ARCH_MMAP_RND_BITS if MMU select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT + select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_TRACEHOOK select HAVE_ARCH_TRANSPARENT_HUGEPAGE -- cgit v1.2.3