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5f501d5556
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Kees Cook 5f501d5556 binfmt_elf: reintroduce using MAP_FIXED_NOREPLACE 
Commit b212921b13 ("elf: don't use MAP_FIXED_NOREPLACE for elf
executable mappings") reverted back to using MAP_FIXED to map ELF LOAD
segments because it was found that the segments in some binaries overlap
and can cause MAP_FIXED_NOREPLACE to fail.

The original intent of MAP_FIXED_NOREPLACE in the ELF loader was to
prevent the silent clobbering of an existing mapping (e.g.  stack) by
the ELF image, which could lead to exploitable conditions.  Quoting
commit 4ed2863951 ("fs, elf: drop MAP_FIXED usage from elf_map"),
which originally introduced the use of MAP_FIXED_NOREPLACE in the
loader:

    Both load_elf_interp and load_elf_binary rely on elf_map to map
    segments [to a specific] address and they use MAP_FIXED to enforce
    that. This is however [a] dangerous thing prone to silent data
    corruption which can be even exploitable.
    ...
    Let's take CVE-2017-1000253 as an example ... we could end up mapping
    [the executable] over the existing stack ... The [stack layout] issue
    has been fixed since then ... So we should be safe and any [similar]
    attack should be impractical. On the other hand this is just too
    subtle [an] assumption ... it can break quite easily and [be] hard to
    spot.
    ...
    Address this [weakness] by changing MAP_FIXED to the newly added
    MAP_FIXED_NOREPLACE. This will mean that mmap will fail if there is
    an existing mapping clashing with the requested one [instead of
    silently] clobbering it.

Then processing ET_DYN binaries the loader already calculates a total
size for the image when the first segment is mapped, maps the entire
image, and then unmaps the remainder before the remaining segments are
then individually mapped.

To avoid the earlier problems (legitimate overlapping LOAD segments
specified in the ELF), apply the same logic to ET_EXEC binaries as well.

For both ET_EXEC and ET_DYN+INTERP use MAP_FIXED_NOREPLACE for the
initial total size mapping and then use MAP_FIXED to build the final
(possibly legitimately overlapping) mappings.  For ET_DYN w/out INTERP,
continue to map at a system-selected address in the mmap region.

Link: https://lkml.kernel.org/r/20210916215947.3993776-1-keescook@chromium.org
Link: https://lore.kernel.org/lkml/1595869887-23307-2-git-send-email-anthony.yznaga@oracle.com
Co-developed-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Chen Jingwen <chenjingwen6@huawei.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrei Vagin <avagin@openvz.org>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-11-09 10:02:50 -08:00
arch include/linux/delay.h: replace kernel.h with the necessary inclusions 2021-11-09 10:02:49 -08:00
block block-5.15-2021-10-29 2021-10-29 11:10:29 -07:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-08-30 12:57:10 -07:00
Documentation Docs/admin-guide/mm/pagemap: wordsmith page flags descriptions 2021-11-06 13:30:46 -07:00
drivers lib, stackdepot: add helper to print stack entries into buffer 2021-11-09 10:02:50 -08:00
fs binfmt_elf: reintroduce using MAP_FIXED_NOREPLACE 2021-11-09 10:02:50 -08:00
include include/linux/string_helpers.h: add linux/string.h for strlen() 2021-11-09 10:02:50 -08:00
init memblock: use memblock_free for freeing virtual pointers 2021-11-06 13:30:41 -07:00
ipc mm,hugetlb: remove mlock ulimit for SHM_HUGETLB 2021-11-09 10:02:48 -08:00
kernel stacktrace: move filter_irq_stacks() to kernel/stacktrace.c 2021-11-06 13:30:43 -07:00
lib mm/scatterlist: replace the !preemptible warning in sg_miter_stop() 2021-11-09 10:02:50 -08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm lib, stackdepot: add helper to print stack entries into buffer 2021-11-09 10:02:50 -08:00
net include/linux/mm.h: move nr_free_buffer_pages from swap.h to mm.h 2021-11-06 13:30:43 -07:00
samples samples/bpf: Relicense bpf_insn.h as GPL-2.0-only OR BSD-2-Clause 2021-09-29 16:03:55 +02:00
scripts checkpatch: get default codespell dictionary path from package location 2021-11-09 10:02:50 -08:00
security mm: remove HARDENED_USERCOPY_FALLBACK 2021-11-06 13:30:43 -07:00
sound ALSA: usb-audio: Fix microphone sound on Jieli webcam. 2021-10-19 08:07:01 +02:00
tools procfs: do not list TID 0 in /proc/<pid>/task 2021-11-09 10:02:48 -08:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Remove tlbs_dirty 2021-09-23 11:01:12 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update email address for Colin King 2021-11-09 10:02:49 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: rectify entry for ALLWINNER HARDWARE SPINLOCK SUPPORT 2021-11-09 10:02:50 -08:00
Makefile Compiler Attributes: add __alloc_size() for better bounds checking 2021-11-06 13:30:33 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.