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Daniel Borkmann 2a5418a13f bpf: improve dead code sanitizing 
Given we recently had c131187db2 ("bpf: fix branch pruning
logic") and 95a762e2c8 ("bpf: fix incorrect sign extension in
check_alu_op()") in particular where before verifier skipped
verification of the wrongly assumed dead branch, we should not
just replace the dead code parts with nops (mov r0,r0). If there
is a bug such as fixed in 95a762e2c8 in future again, where
runtime could execute those insns, then one of the potential
issues with the current setting would be that given the nops
would be at the end of the program, we could execute out of
bounds at some point.

The best in such case would be to just exit the BPF program
altogether and return an exception code. However, given this
would require two instructions, and such a dead code gap could
just be a single insn long, we would need to place 'r0 = X; ret'
snippet at the very end after the user program or at the start
before the program (where we'd skip that region on prog entry),
and then place unconditional ja's into the dead code gap.

While more complex but possible, there's still another block
in the road that currently prevents from this, namely BPF to
BPF calls. The issue here is that such exception could be
returned from a callee, but the caller would not know that
it's an exception that needs to be propagated further down.
Alternative that has little complexity is to just use a ja-1
code for now which will trap the execution here instead of
silently doing bad things if we ever get there due to bugs.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2018-01-26 16:42:05 -08:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2018-01-20 22:03:46 -05:00
block block: drain queue before waiting for q_usage_counter becoming zero 2018-01-05 09:09:48 -07:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2018-01-12 09:47:58 -08:00
Documentation bpf, doc: Correct one wrong value in "Register value tracking" 2018-01-24 16:43:11 +01:00
drivers net: aquantia: make symbol hw_atl_boards static 2018-01-23 10:59:42 -05:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-01-19 22:59:33 -05:00
include bpf: Add BPF_SOCK_OPS_STATE_CB 2018-01-25 16:41:15 -08:00
init Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-01-12 10:23:59 -08:00
ipc Rename superblock flags (MS_xyz -> SB_xyz) 2017-11-27 13:05:09 -08:00
kernel bpf: improve dead code sanitizing 2018-01-26 16:42:05 -08:00
lib bpf: add couple of test cases for signed extended imms 2018-01-19 18:36:59 -08:00
mm mm/page_owner.c: remove drain_all_pages from init_early_allocated_pages 2018-01-19 10:09:40 -08:00
net bpf: xor of a/x in cbpf can be done in 32 bit alu 2018-01-26 16:42:05 -08:00
samples samples/bpf: Partially fixes the bpf.o build 2018-01-26 23:57:10 +01:00
scripts scripts/gdb/linux/tasks.py: fix get_thread_info 2018-01-19 10:09:41 -08:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-01-17 00:10:42 -05:00
sound ALSA: seq: Make ioctls race-free 2018-01-11 14:37:51 +01:00
tools bpf: clean up from test_tcpbpf_kern.c 2018-01-26 23:39:05 +01:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM/ARM Fixes for v4.15, Round 2 2017-12-18 12:57:43 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild misc updates for v4.15 2017-11-17 17:51:33 -08:00
.mailmap mailmap: update Mark Yao's email address 2018-01-04 16:45:09 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS wireless-drivers-next patches for 4.16 2018-01-19 10:26:53 -05:00
Makefile Linux 4.15-rc8 2018-01-14 15:32:30 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.