Commit c715b72c authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds

mm: revert x86_64 and arm64 ELF_ET_DYN_BASE base changes

Moving the x86_64 and arm64 PIE base from 0x555555554000 to 0x000100000000
broke AddressSanitizer.  This is a partial revert of:

  eab09532 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE")
  02445990 ("arm64: move ELF_ET_DYN_BASE to 4GB / 4MB")

The AddressSanitizer tool has hard-coded expectations about where
executable mappings are loaded.

The motivation for changing the PIE base in the above commits was to
avoid the Stack-Clash CVEs that allowed executable mappings to get too
close to heap and stack.  This was mainly a problem on 32-bit, but the
64-bit bases were moved too, in an effort to proactively protect those
systems (proofs of concept do exist that show 64-bit collisions, but
other recent changes to fix stack accounting and setuid behaviors will
minimize the impact).

The new 32-bit PIE base is fine for ASan (since it matches the ET_EXEC
base), so only the 64-bit PIE base needs to be reverted to let x86 and
arm64 ASan binaries run again.  Future changes to the 64-bit PIE base on
these architectures can be made optional once a more dynamic method for
dealing with AddressSanitizer is found.  (e.g.  always loading PIE into
the mmap region for marked binaries.)

Link: http://lkml.kernel.org/r/20170807201542.GA21271@beast
Fixes: eab09532 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE")
Fixes: 02445990 ("arm64: move ELF_ET_DYN_BASE to 4GB / 4MB")
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Reported-by: default avatarKostya Serebryany <kcc@google.com>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 704b862f
......@@ -114,10 +114,10 @@
/*
* 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
* 64-bit, this is above 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 0x100000000UL
#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3)
#ifndef __ASSEMBLY__
......
......@@ -247,11 +247,11 @@ extern int force_personality32;
/*
* 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
* 64-bit, this is above 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 (mmap_is_ia32() ? 0x000400000UL : \
0x100000000UL)
(TASK_SIZE / 3 * 2))
/* This yields a mask that user programs can use to figure out what
instruction set this CPU supports. This could be done in user space,
......
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