Patch "arm: move ELF_ET_DYN_BASE to 4MB" has been added to the 4.12-stable tree

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

arm: move ELF_ET_DYN_BASE to 4MB

to the 4.12-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:
arm-move-elf_et_dyn_base-to-4mb.patch
and it can be found in the queue-4.12 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 15:52:40 -0700
Subject: arm: move ELF_ET_DYN_BASE to 4MB

From: Kees Cook <[email protected]>

commit 6a9af90a3bcde217a1c053e135f5f43e5d5fafbd 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.

4MB is chosen here mainly to have parity with x86, where this is the traditional 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 ARM the position could be 0x8000, the standard ET_EXEC load address, but that is needlessly close to the NULL address, and anyone running PIE on 32-bit ARM will have an MMU, so the tight mapping is not needed.

---
 arch/arm/include/asm/elf.h |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

@@ -112,12 +112,8 @@ int dump_task_regs(struct task_struct *t
 #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.  */
-
-#define ELF_ET_DYN_BASE	(TASK_SIZE / 3 * 2)
+/* This is the base location for PIE (ET_DYN with INTERP) loads. */
+#define ELF_ET_DYN_BASE		0x400000UL
 
 /* When the program starts, a1 contains a pointer to a function to be 
    registered with atexit, as per the SVR4 ABI.  A value of 0 means we 

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

queue-4.12/binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch queue-4.12/s390-reduce-elf_et_dyn_base.patch queue-4.12/arm-move-elf_et_dyn_base-to-4mb.patch queue-4.12/arm64-move-elf_et_dyn_base-to-4gb-4mb.patch queue-4.12/powerpc-move-elf_et_dyn_base-to-4gb-4mb.patch