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Marco Elver cc0a0f9855 kfence: introduce burst mode 
Introduce burst mode, which can be configured with kfence.burst=$count,
where the burst count denotes the additional successive slab allocations
to be allocated through KFENCE for each sample interval.

The idea is that this can give developers an additional knob to make
KFENCE more aggressive when debugging specific issues of systems where
either rebooting or recompiling the kernel with KASAN is not possible.

Experiment: To assess the effectiveness of the new option, we randomly
picked a recent out-of-bounds [1] and use-after-free bug [2], each with a
reproducer provided by syzbot, that initially detected these bugs with
KASAN.  We then tried to reproduce the bugs with KFENCE below.

[1] Fixed by: 7c55b78818 ("jfs: xattr: fix buffer overflow for invalid xattr")
    https://syzkaller.appspot.com/bug?id=9d1b59d4718239da6f6069d3891863c25f9f24a2
[2] Fixed by: f8ad00f3fb ("l2tp: fix possible UAF when cleaning up tunnels")
    https://syzkaller.appspot.com/bug?id=4f34adc84f4a3b080187c390eeef60611fd450e1

The following KFENCE configs were compared. A pool size of 1023 objects
was used for all configurations.

	Baseline
		kfence.sample_interval=100
		kfence.skip_covered_thresh=75
		kfence.burst=0

	Aggressive
		kfence.sample_interval=1
		kfence.skip_covered_thresh=10
		kfence.burst=0

	AggressiveBurst
		kfence.sample_interval=1
		kfence.skip_covered_thresh=10
		kfence.burst=1000

Each reproducer was run 10 times (after a fresh reboot), with the
following detection counts for each KFENCE config:

                    | Detection Count out of 10 |
                    |    OOB [1]  |    UAF [2]  |
  ------------------+-------------+-------------+
  Default           |     0/10    |     0/10    |
  Aggressive        |     0/10    |     0/10    |
  AggressiveBurst   |     8/10    |     8/10    |

With the Default and even the Aggressive configs the results are
unsurprising, given KFENCE has not been designed for deterministic bug
detection of small test cases.

However, when enabling burst mode with relatively large burst count,
KFENCE can start to detect heap memory-safety bugs even in simpler test
cases with high probability (in the above cases with ~80% probability).

Link: https://lkml.kernel.org/r/20240805124203.2692278-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-09-01 20:26:03 -07:00
arch s390/mm/fault: convert do_secure_storage_access() from follow_page() to folio_walk 2024-09-01 20:26:01 -07:00
block block: fix detection of unsupported WRITE SAME in blkdev_issue_write_zeroes 2024-08-28 08:49:25 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto crypto: testmgr - generate power-of-2 lengths more often 2024-07-13 11:50:28 +12:00
Documentation kfence: introduce burst mode 2024-09-01 20:26:03 -07:00
drivers mm: kvmalloc: align kvrealloc() with krealloc() 2024-09-01 20:25:44 -07:00
fs mm/hugetlb: remove hugetlb_follow_page_mask() leftover 2024-09-01 20:25:57 -07:00
include kfence: introduce burst mode 2024-09-01 20:26:03 -07:00
init mm: fix typo in Kconfig 2024-09-01 20:25:45 -07:00
io_uring io_uring/kbuf: return correct iovec count from classic buffer peek 2024-08-30 10:45:54 -06:00
ipc sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
kernel mm: create promo_wmark_pages and clean up open-coded sites 2024-09-01 20:25:58 -07:00
lib lib: test_hmm: use min() to improve dmirror_exclusive() 2024-09-01 20:25:52 -07:00
LICENSES
mm kfence: introduce burst mode 2024-09-01 20:26:03 -07:00
net Including fixes from bluetooth, wireless and netfilter. 2024-08-30 06:14:39 +12:00
rust Rust fixes for v6.11 2024-08-16 11:24:06 -07:00
samples kmemleak-test: add percpu leak 2024-09-01 20:25:50 -07:00
scripts net: drop special comment style 2024-08-23 10:21:02 +01:00
security Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging 2024-09-01 09:18:48 +12:00
sound sound fixes for 6.11-rc6 2024-08-28 06:24:22 +12:00
tools tools: add skeleton code for userland testing of VMA logic 2024-09-01 20:25:55 -07:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: Disallow read-only memslots for SEV-ES and SEV-SNP (and TDX) 2024-08-14 12:28:24 -04:00
.clang-format Docs: Move clang-format from process/ to dev-tools/ 2024-06-26 16:36:00 -06:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: add script and target to generate pacman package 2024-07-22 01:24:22 +09:00
.mailmap ARM: SoC fixes for 6.11, part 2 2024-09-01 06:42:13 +12:00
.rustfmt.toml
COPYING
CREDITS tracing: Update of MAINTAINERS and CREDITS file 2024-07-18 14:08:42 -07:00
Kbuild
Kconfig
MAINTAINERS tools: add skeleton code for userland testing of VMA logic 2024-09-01 20:25:55 -07:00
Makefile Linux 6.11-rc6 2024-09-01 19:46:02 +12:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.