This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
GCC provides reasonable memset/memcpy functions itself, with __builtin_memset
and __builtin_memcpy. For the "unknown" cases, it'll fall back to our
current existing functions, but for fixed size versions it'll inline
something smart. Quite often that will be the same as we have now,
but sometimes it can do something smarter (for example, if the code
then sets the first member of a struct, it can do a shorter memset).
In addition, and this is more important, gcc knows which registers and
such are not clobbered (while for our asm version it pretty much
acts like a compiler barrier), so for various cases it can avoid reloading
values.
The effect on codesize is shown below on my typical laptop .config:
text data bss dec hex filename
5605675 2041100 6525148 14171923 d83f13 vmlinux.before
5595849 2041668 6525148 14162665 d81ae9 vmlinux.after
Due to some not-so-good behavior in the gcc 3.x series, this change
is only done for GCC 4.x and above.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20090928142122.6fc57e9c@infradead.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Cc: Vegard Nossum <vegardno@ifi.uio.no>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alok N Kataria <akataria@vmware.com>
Cc: "Tan Wei Chong" <wei.chong.tan@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Bob Moore <robert.moore@intel.com>
LKML-Reference: <1253137123-18047-2-git-send-email-felipe.contreras@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
The hooks that we modify are:
- Page fault handler (to handle kmemcheck faults)
- Debug exception handler (to hide pages after single-stepping
the instruction that caused the page fault)
Also redefine memset() to use the optimized version if kmemcheck is
enabled.
(Thanks to Pekka Enberg for minimizing the impact on the page fault
handler.)
As kmemcheck doesn't handle MMX/SSE instructions (yet), we also disable
the optimized xor code, and rely instead on the generic C implementation
in order to avoid false-positive warnings.
Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>
[whitespace fixlet]
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>
Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:
a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Daniel Micay