For all mpm wrapper functions, check minlen vs the input buffer to see
if we can bypass the mpm search.
Next to this, make all the function inline. Also constify the input and
do other minor cleanups.
FreeBSD 10 32-bit with clang 3.3:
log-tlslog.c:172:14: error: format specifies type 'long' but the argument has type 'time_t' (aka 'int') [-Werror,-Wformat]
p->ts.tv_sec,
^~~~~~~~~~~~
1 error generated.
detect-engine-payload.c:508:27: warning: format specifies type 'long' but the argument has type 'time_t' (aka 'int') [-Wformat]
printf("%ld.%06ld\n", tv_diff.tv_sec, (long int)tv_diff.tv_usec);
~~~ ^~~~~~~~~~~~~~
%d
1 warning generated.
The old behaviour of returning a failure if we found a pattern while
matching on negated content is now changed to continuing searching
for other combinations where we don't find the pattern for the
negated content.
Thanks to Will Metcalf for reporting this.
Aho-Corasick mpm optimized for Tilera Tile-Gx architecture. Based on the
util-mpm-ac.c code base. The primary optimizations are:
1) Matching function used Tilera specific instructions.
2) Alphabet compression to reduce delta table size to increase cache
utilization and performance.
The basic observation is that not all 256 ASCII characters are used by
the set of multiple patterns in a group for which a DFA is
created. The first reason is that Suricata's pattern matching is
case-insensitive, so all uppercase characters are converted to
lowercase, leaving a hole of 26 characters in the
alphabet. Previously, this hole was simply left in the middle of the
alphabet and thus in the generated Next State (delta) tables.
A new, smaller, alphabet is created using a translation table of 256
bytes per mpm group. Previously, there was one global translation
table for converting upper case to lowercase.
Additional, unused characters are found by creating a histogram of all
the characters in all the patterns. Then all the characters with zero
counts are mapped to one character (0) in the new alphabet. Since
These characters appear in no pattern, they can all be mapped to a
single character and still result in the same matches being
found. Zero was chosen for the value in the new alphabet since this
"character" is more likely to appear in the input. The unused
character always results in the next state being state zero, but that
fact is not currently used by the code, since special casing takes
additional instructions.
The characters that do appear in some pattern are mapped to
consecutive characters in the new alphabet, starting at 1. This
results in a dense packing of next state values in the delta tables
and additionally can allow for a smaller number of columns in that
table, thus using less memory and better packing into the cache. The
size of the new alphabet is the number of used characters plus 1 for
the unused catch-all character.
The alphabet size is rounded up to the next larger power-of-2 so that
multiplication by the alphabet size can be done with a shift. It
might be possible to use a multiply instruction, so that the exact
alphabet size could be used, which would further reduce the size of
the delta tables, increase cache density and not require the
specialized search functions. The multiply would likely add 1 cycle to
the inner search loop.
Since the multiply by alphabet-size is cleverly merged with a mask
instruction (in the SINDEX macro), specialized versions of the
SCACSearch function are generated for alphabet sizes 256, 128, 64, 32
and 16. This is done by including the file util-mpm-ac-small.c
multiple times with a redefined SINDEX macro. A function pointer is
then stored in the mpm context for the search function. For alpha bit
sizes of 8 or smaller, the number of states usually small, so the DFA
is already very small, so there is little difference using the 16
state search function.
The SCACSearch function is also specialized by the size of the value
stored in the next state (delta) tables, either 16-bits or 32-bits.
This removes a conditional inside the Search function. That
conditional is only called once, but doesn't hurt to remove
it. 16-bits are used for up to 32K states, with the sign bit set for
states with matches.
Future optimization:
The state-has-match values is only needed per state, not per next
state, so checking the next-state sign bit could be replaced with
reading a different value, at the cost of an additional load, but
increasing the 16-bit next state span to 64K.
Since the order of the characters in the new alphabet doesn't matter,
the new alphabet could be sorted by the frequency of the characters in
the expected input stream for that multi-pattern matcher. This would
group more frequent characters into the same cache lines, thus
increasing the probability of reusing a cache-line.
All the next state values for each state live in their own set of
cache-lines. With power-of-two sizes alphabets, these don't overlap.
So either 32 or 16 character's next states are loaded in each cache
line load. If the alphabet size is not an exact power-of-2, then the
last cache-line is not completely full and up to 31*2 bytes of that
line could be wasted per state.
The next state table could be transposed, so that all the next states
for a specific character are stored sequentially, this could be better
if some characters, for example the unused character, are much more
frequent.
Now depth is kept in mind when we inspect chunks in client/server body.
This takes care of FPs originating from inspecting subsequent chunks that
match with depth, but shouldn't.
- suricata treates sigs with offset/depth without any packet keywords as stream sigs
- as a consequence suricata will FN on such sigs
The tests introduced here will fail, displaying the issues. The
next patch in the series would fix the said issues.
commit eff08f93d8
Author: Anoop Saldanha <poonaatsoc@gmail.com>
Date: Thu Nov 3 14:31:24 2011 +0530
update failing unittest to reflect the mpm design update
Fixed a bug in the mpm code that would make all the changes in the commit just undone wrong.
This patch adds support for the replace keyword. It is used with
content to change selected part of the payload. The major point
with this patch is that having a replace keyword made necessary
to avoid all stream level check because we need to access to the
could-be-modified packet payload.
One of the main difficulty is to handle complex signature. If there is
other content check, we must do the substitution when we're sure all
match are valid. The patch adds an attribute to the thread context
variable to be able to deal with recursivity of the match function.
Replace is only activated in IPS mode and apply only to raw match.
Victor Julien
Ken Steele
Anoop Saldanha
Anoop Saldanha
Eric Leblond
William Metcalf
Gurvinder Singh