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authorLinus Torvalds <torvalds@linux-foundation.org>2016-07-26 13:05:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-07-26 13:05:11 -0700
commit0f776dc377f6c87f4e4d4a5f63602f33fb93b31e (patch)
tree25811858d15be4c526c6c887d8c41c0546edd6b9 /Documentation/security
parent015cd867e566e3a27b5e8062eb24eeaa4d77297f (diff)
parenta88b1672d4ddf9895eb53e6980926d5e960dea8e (diff)
Merge tag 'docs-for-linus' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet: "Some big changes this month, headlined by the addition of a new formatted documentation mechanism based on the Sphinx system. The objectives here are to make it easier to create better-integrated (and more attractive) documents while (eventually) dumping our one-of-a-kind, cobbled-together system for something that is widely used and maintained by others. There's a fair amount of information what's being done, why, and how to use it in: https://lwn.net/Articles/692704/ https://lwn.net/Articles/692705/ Closer to home, Documentation/kernel-documentation.rst describes how it works. For now, the new system exists alongside the old one; you should soon see the GPU documentation converted over in the DRM pull and some significant media conversion work as well. Once all the docs have been moved over and we're convinced that the rough edges (of which are are a few) have been smoothed over, the DocBook-based stuff should go away. Primary credit is to Jani Nikula for doing the heavy lifting to make this stuff actually work; there has also been notable effort from Markus Heiser, Daniel Vetter, and Mauro Carvalho Chehab. Expect a couple of conflicts on the new index.rst file over the course of the merge window; they are trivially resolvable. That file may be a bit of a conflict magnet in the short term, but I don't expect that situation to last for any real length of time. Beyond that, of course, we have the usual collection of tweaks, updates, and typo fixes" * tag 'docs-for-linus' of git://git.lwn.net/linux: (77 commits) doc-rst: kernel-doc: fix handling of address_space tags Revert "doc/sphinx: Enable keep_warnings" doc-rst: kernel-doc directive, fix state machine reporter docs: deprecate kernel-doc-nano-HOWTO.txt doc/sphinx: Enable keep_warnings Documentation: add watermark_scale_factor to the list of vm systcl file kernel-doc: Fix up warning output docs: Get rid of some kernel-documentation warnings doc-rst: add an option to ignore DocBooks when generating docs workqueue: Fix a typo in workqueue.txt Doc: ocfs: Fix typo in filesystems/ocfs2-online-filecheck.txt Documentation/sphinx: skip build if user requested specific DOCBOOKS Documentation: add cleanmediadocs to the documentation targets Add .pyc files to .gitignore Doc: PM: Fix a typo in intel_powerclamp.txt doc-rst: flat-table directive - initial implementation Documentation: add meta-documentation for Sphinx and kernel-doc Documentation: tiny typo fix in usb/gadget_multi.txt Documentation: fix wrong value in md.txt bcache: documentation formatting, edited for clarity, stripe alignment notes ...
Diffstat (limited to 'Documentation/security')
-rw-r--r--Documentation/security/self-protection.txt28
1 files changed, 18 insertions, 10 deletions
diff --git a/Documentation/security/self-protection.txt b/Documentation/security/self-protection.txt
index babd6378ec05..3010576c9fca 100644
--- a/Documentation/security/self-protection.txt
+++ b/Documentation/security/self-protection.txt
@@ -183,8 +183,9 @@ provide meaningful defenses.
### Canaries, blinding, and other secrets
It should be noted that things like the stack canary discussed earlier
-are technically statistical defenses, since they rely on a (leakable)
-secret value.
+are technically statistical defenses, since they rely on a secret value,
+and such values may become discoverable through an information exposure
+flaw.
Blinding literal values for things like JITs, where the executable
contents may be partially under the control of userspace, need a similar
@@ -199,8 +200,8 @@ working?) in order to maximize their success.
Since the location of kernel memory is almost always instrumental in
mounting a successful attack, making the location non-deterministic
raises the difficulty of an exploit. (Note that this in turn makes
-the value of leaks higher, since they may be used to discover desired
-memory locations.)
+the value of information exposures higher, since they may be used to
+discover desired memory locations.)
#### Text and module base
@@ -222,14 +223,21 @@ become more difficult to locate.
Much of the kernel's dynamic memory (e.g. kmalloc, vmalloc, etc) ends up
being relatively deterministic in layout due to the order of early-boot
initializations. If the base address of these areas is not the same
-between boots, targeting them is frustrated, requiring a leak specific
-to the region.
+between boots, targeting them is frustrated, requiring an information
+exposure specific to the region.
+
+#### Structure layout
+
+By performing a per-build randomization of the layout of sensitive
+structures, attacks must either be tuned to known kernel builds or expose
+enough kernel memory to determine structure layouts before manipulating
+them.
-## Preventing Leaks
+## Preventing Information Exposures
Since the locations of sensitive structures are the primary target for
-attacks, it is important to defend against leaks of both kernel memory
+attacks, it is important to defend against exposure of both kernel memory
addresses and kernel memory contents (since they may contain kernel
addresses or other sensitive things like canary values).
@@ -250,8 +258,8 @@ sure structure holes are cleared.
When releasing memory, it is best to poison the contents (clear stack on
syscall return, wipe heap memory on a free), to avoid reuse attacks that
rely on the old contents of memory. This frustrates many uninitialized
-variable attacks, stack info leaks, heap info leaks, and use-after-free
-attacks.
+variable attacks, stack content exposures, heap content exposures, and
+use-after-free attacks.
### Destination tracking