Patch "s390: reduce ELF_ET_DYN_BASE" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

s390: reduce ELF_ET_DYN_BASE

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     s390-reduce-elf_et_dyn_base.patch

and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Kees Cook <[email protected]>
Date: Mon, 10 Jul 2017 15:52:51 -0700
Subject: s390: reduce ELF_ET_DYN_BASE

From: Kees Cook <[email protected]>

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.

---
 arch/s390/include/asm/elf.h |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

@@ -158,14 +158,13 @@ extern unsigned int vdso_enabled;
 #define CORE_DUMP_USE_REGSET
 #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
-   the loader.  We need to make sure that it is out of the way of the program
-   that it will "exec", and that there is sufficient room for the brk. 64-bit
-   tasks are aligned to 4GB. */
-#define ELF_ET_DYN_BASE (is_compat_task() ? \
-				(STACK_TOP / 3 * 2) : \
-				(STACK_TOP / 3 * 2) & ~((1UL << 32) - 1))
+/*
+ * This is the base location for PIE (ET_DYN with INTERP) loads. On
+ * 64-bit, this is raised to 4GB to leave the entire 32-bit address
+ * space open for things that want to use the area for 32-bit pointers.
+ */
+#define ELF_ET_DYN_BASE		(is_compat_task() ? 0x000400000UL : \
+						    0x100000000UL)
 
 /* This yields a mask that user programs can use to figure out what
    instruction set this CPU supports. */

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch queue-4.9/exec-limit-arg-stack-to-at-most-75-of-_stk_lim.patch queue-4.9/s390-reduce-elf_et_dyn_base.patch queue-4.9/arm-move-elf_et_dyn_base-to-4mb.patch queue-4.9/arm64-move-elf_et_dyn_base-to-4gb-4mb.patch queue-4.9/selftests-capabilities-fix-the-test_execve-test.patch queue-4.9/powerpc-move-elf_et_dyn_base-to-4gb-4mb.patch