mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-28 14:44:10 +08:00
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 above 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 below 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: d1fd836dcf
("mm: split ET_DYN ASLR from mmap ASLR")
Link: http://lkml.kernel.org/r/20170621173201.GA114489@beast
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Qualys Security Advisory <qsa@qualys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
c257a340ed
commit
eab09532d4
@ -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,
|
||||
|
@ -927,17 +927,60 @@ static int load_elf_binary(struct linux_binprm *bprm)
|
||||
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) {
|
||||
|
Loading…
Reference in New Issue
Block a user