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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
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eab09532d4
@ -245,12 +245,13 @@ extern int force_personality32;
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#define CORE_DUMP_USE_REGSET
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#define ELF_EXEC_PAGESIZE 4096
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/* This is the location that an ET_DYN program is loaded if exec'ed. Typical
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use of this is to invoke "./ld.so someprog" to test out a new version of
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the loader. We need to make sure that it is out of the way of the program
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that it will "exec", and that there is sufficient room for the brk. */
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#define ELF_ET_DYN_BASE (TASK_SIZE / 3 * 2)
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/*
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* This is the base location for PIE (ET_DYN with INTERP) loads. On
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* 64-bit, this is raised to 4GB to leave the entire 32-bit address
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* space open for things that want to use the area for 32-bit pointers.
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*/
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#define ELF_ET_DYN_BASE (mmap_is_ia32() ? 0x000400000UL : \
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0x100000000UL)
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/* This yields a mask that user programs can use to figure out what
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instruction set this CPU supports. This could be done in user space,
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@ -927,17 +927,60 @@ static int load_elf_binary(struct linux_binprm *bprm)
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elf_flags = MAP_PRIVATE | MAP_DENYWRITE | MAP_EXECUTABLE;
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vaddr = elf_ppnt->p_vaddr;
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/*
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* If we are loading ET_EXEC or we have already performed
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* the ET_DYN load_addr calculations, proceed normally.
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*/
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if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
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elf_flags |= MAP_FIXED;
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} else if (loc->elf_ex.e_type == ET_DYN) {
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/* Try and get dynamic programs out of the way of the
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* default mmap base, as well as whatever program they
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* might try to exec. This is because the brk will
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* follow the loader, and is not movable. */
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load_bias = ELF_ET_DYN_BASE - vaddr;
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if (current->flags & PF_RANDOMIZE)
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load_bias += arch_mmap_rnd();
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load_bias = ELF_PAGESTART(load_bias);
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/*
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* This logic is run once for the first LOAD Program
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* Header for ET_DYN binaries to calculate the
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* randomization (load_bias) for all the LOAD
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* Program Headers, and to calculate the entire
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* size of the ELF mapping (total_size). (Note that
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* load_addr_set is set to true later once the
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* initial mapping is performed.)
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*
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* There are effectively two types of ET_DYN
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* binaries: programs (i.e. PIE: ET_DYN with INTERP)
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* and loaders (ET_DYN without INTERP, since they
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* _are_ the ELF interpreter). The loaders must
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* be loaded away from programs since the program
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* may otherwise collide with the loader (especially
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* for ET_EXEC which does not have a randomized
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* position). For example to handle invocations of
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* "./ld.so someprog" to test out a new version of
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* the loader, the subsequent program that the
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* loader loads must avoid the loader itself, so
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* they cannot share the same load range. Sufficient
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* room for the brk must be allocated with the
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* loader as well, since brk must be available with
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* the loader.
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*
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* Therefore, programs are loaded offset from
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* ELF_ET_DYN_BASE and loaders are loaded into the
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* independently randomized mmap region (0 load_bias
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* without MAP_FIXED).
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*/
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if (elf_interpreter) {
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load_bias = ELF_ET_DYN_BASE;
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if (current->flags & PF_RANDOMIZE)
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load_bias += arch_mmap_rnd();
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elf_flags |= MAP_FIXED;
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} else
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load_bias = 0;
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/*
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* Since load_bias is used for all subsequent loading
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* calculations, we must lower it by the first vaddr
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* so that the remaining calculations based on the
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* ELF vaddrs will be correctly offset. The result
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* is then page aligned.
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*/
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load_bias = ELF_PAGESTART(load_bias - vaddr);
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total_size = total_mapping_size(elf_phdata,
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loc->elf_ex.e_phnum);
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if (!total_size) {
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