Commit fbc877cd authored Jul 10, 2017 by Kees Cook Committed by Greg Kroah-Hartman Jul 21, 2017

s390: reduce ELF_ET_DYN_BASE

commit a73dc5370e153ac63718d850bddf0c9aa9d871e6 upstream.

Now that explicitly executed loaders are loaded in the mmap region, we
have more freedom to decide where we position PIE binaries in the
address space to avoid possible collisions with mmap or stack regions.

For 64-bit, align to 4GB to allow runtimes to use the entire 32-bit
address space for 32-bit pointers.  On 32-bit use 4MB, which is the
traditional x86 minimum load location, likely to avoid historically
requiring a 4MB page table entry when only a portion of the first 4MB
would be used (since the NULL address is avoided).  For s390 the
position could be 0x10000, but that is needlessly close to the NULL
address.

Link: http://lkml.kernel.org/r/1498154792-49952-5-git-send-email-keescook@chromium.org


Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 90fb0f7a

arch/s390/include/asm/elf.h

+7 −8

Original line number	Original line	Diff line number	Diff line
	@@ -158,14 +158,13 @@ extern unsigned int vdso_enabled;
	#define CORE_DUMP_USE_REGSET		#define CORE_DUMP_USE_REGSET
	#define ELF_EXEC_PAGESIZE 4096		#define ELF_EXEC_PAGESIZE 4096

	/* This is the location that an ET_DYN program is loaded if exec'ed. Typical		/*
	use of this is to invoke "./ld.so someprog" to test out a new version of		* This is the base location for PIE (ET_DYN with INTERP) loads. On
	the loader. We need to make sure that it is out of the way of the program		* 64-bit, this is raised to 4GB to leave the entire 32-bit address
	that it will "exec", and that there is sufficient room for the brk. 64-bit		* space open for things that want to use the area for 32-bit pointers.
	tasks are aligned to 4GB. */		*/
	#define ELF_ET_DYN_BASE (is_compat_task() ? \		#define ELF_ET_DYN_BASE (is_compat_task() ? 0x000400000UL : \
	(STACK_TOP / 3 * 2) : \		0x100000000UL)
	(STACK_TOP / 3 * 2) & ~((1UL << 32) - 1))

	/* This yields a mask that user programs can use to figure out what		/* This yields a mask that user programs can use to figure out what
	instruction set this CPU supports. */		instruction set this CPU supports. */