+ binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch added to -mm tree

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The patch titled
     Subject: binfmt_elf: use ELF_ET_DYN_BASE only for PIE
has been added to the -mm tree.  Its filename is
     binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch

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------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: binfmt_elf: use ELF_ET_DYN_BASE only for PIE

The ELF_ET_DYN_BASE position was originally intended to keep loaders away
from ET_EXEC binaries.  (For example, running "/lib/ld-linux.so.2
/bin/cat" might cause the subsequent load of /bin/cat into where the
loader had been loaded.) With the advent of PIE (ET_DYN binaries with an
INTERP Program Header), ELF_ET_DYN_BASE continued to be used since the
kernel was only looking at ET_DYN.  However, since ELF_ET_DYN_BASE is
traditionally set at the top 1/3rd of the TASK_SIZE, a substantial portion
of the address space is unused.

For 32-bit tasks when RLIMIT_STACK is set to RLIM_INFINITY, programs are
loaded below the mmap region.  This means they can be made to collide
(CVE-2017-1000370) or nearly collide (CVE-2017-1000371) with pathological
stack regions.  Lowering ELF_ET_DYN_BASE solves both by moving programs
above the mmap region in all cases, and will now additionally avoid
programs falling back to the mmap region by enforcing MAP_FIXED for
program loads (i.e.  if it would have collided with the stack, now it will
fail to load instead of falling back to the mmap region).

To allow for a lower ELF_ET_DYN_BASE, loaders (ET_DYN without INTERP) are
loaded into the mmap region, leaving space available for either an ET_EXEC
binary with a fixed location or PIE being loaded into mmap by the loader. 
Only PIE programs are loaded offset from ELF_ET_DYN_BASE, which means
architectures can now safely lower their values without risk of loaders
colliding with their subsequently loaded programs.

For 64-bit, ELF_ET_DYN_BASE is best set to 4GB to allow runtimes to use
the entire 32-bit address space for 32-bit pointers.

Thanks to PaX Team, Daniel Micay, and Rik van Riel for inspiration and
suggestions on how to implement this solution.

Fixes: d1fd836dcf00 ("mm: split ET_DYN ASLR from mmap ASLR")
Link: http://lkml.kernel.org/r/20170621173201.GA114489@beast
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Daniel Micay <danielmicay@xxxxxxxxx>
Cc: Qualys Security Advisory <qsa@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Grzegorz Andrejczuk <grzegorz.andrejczuk@xxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: James Hogan <james.hogan@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Pratyush Anand <panand@xxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 arch/x86/include/asm/elf.h |   13 ++++---
 fs/binfmt_elf.c            |   59 ++++++++++++++++++++++++++++++-----
 2 files changed, 58 insertions(+), 14 deletions(-)

diff -puN arch/x86/include/asm/elf.h~binfmt_elf-use-elf_et_dyn_base-only-for-pie arch/x86/include/asm/elf.h
--- a/arch/x86/include/asm/elf.h~binfmt_elf-use-elf_et_dyn_base-only-for-pie
+++ a/arch/x86/include/asm/elf.h
@@ -245,12 +245,13 @@ extern int force_personality32;
 #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. 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		(mmap_is_ia32() ? 0x000400000UL : \
+						  0x100000000UL)
 
 /* 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,
diff -puN fs/binfmt_elf.c~binfmt_elf-use-elf_et_dyn_base-only-for-pie fs/binfmt_elf.c
--- a/fs/binfmt_elf.c~binfmt_elf-use-elf_et_dyn_base-only-for-pie
+++ a/fs/binfmt_elf.c
@@ -927,17 +927,60 @@ static int load_elf_binary(struct linux_
 		elf_flags = MAP_PRIVATE | MAP_DENYWRITE | MAP_EXECUTABLE;
 
 		vaddr = elf_ppnt->p_vaddr;
+		/*
+		 * If we are loading ET_EXEC or we have already performed
+		 * the ET_DYN load_addr calculations, proceed normally.
+		 */
 		if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
 			elf_flags |= MAP_FIXED;
 		} else if (loc->elf_ex.e_type == ET_DYN) {
-			/* Try and get dynamic programs out of the way of the
-			 * default mmap base, as well as whatever program they
-			 * might try to exec.  This is because the brk will
-			 * follow the loader, and is not movable.  */
-			load_bias = ELF_ET_DYN_BASE - vaddr;
-			if (current->flags & PF_RANDOMIZE)
-				load_bias += arch_mmap_rnd();
-			load_bias = ELF_PAGESTART(load_bias);
+			/*
+			 * This logic is run once for the first LOAD Program
+			 * Header for ET_DYN binaries to calculate the
+			 * randomization (load_bias) for all the LOAD
+			 * Program Headers, and to calculate the entire
+			 * size of the ELF mapping (total_size). (Note that
+			 * load_addr_set is set to true later once the
+			 * initial mapping is performed.)
+			 *
+			 * There are effectively two types of ET_DYN
+			 * binaries: programs (i.e. PIE: ET_DYN with INTERP)
+			 * and loaders (ET_DYN without INTERP, since they
+			 * _are_ the ELF interpreter). The loaders must
+			 * be loaded away from programs since the program
+			 * may otherwise collide with the loader (especially
+			 * for ET_EXEC which does not have a randomized
+			 * position). For example to handle invocations of
+			 * "./ld.so someprog" to test out a new version of
+			 * the loader, the subsequent program that the
+			 * loader loads must avoid the loader itself, so
+			 * they cannot share the same load range. Sufficient
+			 * room for the brk must be allocated with the
+			 * loader as well, since brk must be available with
+			 * the loader.
+			 *
+			 * Therefore, programs are loaded offset from
+			 * ELF_ET_DYN_BASE and loaders are loaded into the
+			 * independently randomized mmap region (0 load_bias
+			 * without MAP_FIXED).
+			 */
+			if (elf_interpreter) {
+				load_bias = ELF_ET_DYN_BASE;
+				if (current->flags & PF_RANDOMIZE)
+					load_bias += arch_mmap_rnd();
+				elf_flags |= MAP_FIXED;
+			} else
+				load_bias = 0;
+
+			/*
+			 * Since load_bias is used for all subsequent loading
+			 * calculations, we must lower it by the first vaddr
+			 * so that the remaining calculations based on the
+			 * ELF vaddrs will be correctly offset. The result
+			 * is then page aligned.
+			 */
+			load_bias = ELF_PAGESTART(load_bias - vaddr);
+
 			total_size = total_mapping_size(elf_phdata,
 							loc->elf_ex.e_phnum);
 			if (!total_size) {
_

Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are

binfmt_elf-use-elf_et_dyn_base-only-for-pie.patch
arm-reduce-elf_et_dyn_base.patch
arm64-reduce-elf_et_dyn_base.patch
powerpc-reduce-elf_et_dyn_base.patch
s390-reduce-elf_et_dyn_base.patch
ipc-drop-non-rcu-allocation.patch
ipc-sem-do-not-use-ipc_rcu_free.patch
ipc-shm-do-not-use-ipc_rcu_free.patch
ipc-msg-do-not-use-ipc_rcu_free.patch
ipc-util-drop-ipc_rcu_free.patch
ipc-sem-avoid-ipc_rcu_alloc.patch
ipc-shm-avoid-ipc_rcu_alloc.patch
ipc-msg-avoid-ipc_rcu_alloc.patch
ipc-util-drop-ipc_rcu_alloc.patch
ipc-move-atomic_set-to-where-it-is-needed.patch
ipc-shm-remove-special-shm_alloc-free.patch
ipc-msg-remove-special-msg_alloc-free.patch
ipc-sem-drop-__sem_free.patch
efi-avoid-fortify-checks-in-efi-stub.patch
x86-power-64-use-char-arrays-for-asm-function-names.patch
kexec_file-adjust-declaration-of-kexec_purgatory.patch
ib-rxe-do-not-copy-extra-stack-memory-to-skb.patch

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