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feat: selectively zero match lists #2087

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feat: selectively zero match lists #2087

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20 changes: 10 additions & 10 deletions libyara/exec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1438,7 +1438,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)

case OP_FOUND:
pop(r1);
r2.i = context->matches[r1.s->idx].tail != NULL ? 1 : 0;
r2.i = context->matches.entries[r1.s->idx].tail != NULL ? 1 : 0;
YR_DEBUG_FPRINTF(
2,
stderr,
Expand All @@ -1460,7 +1460,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
ensure_within_rules_arena(r2.p);
#endif

match = context->matches[r2.s->idx].head;
match = context->matches.entries[r2.s->idx].head;
r3.i = false;

while (match != NULL)
Expand Down Expand Up @@ -1494,7 +1494,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
ensure_within_rules_arena(r3.p);
#endif

match = context->matches[r3.s->idx].head;
match = context->matches.entries[r3.s->idx].head;
r4.i = false;

while (match != NULL && !r4.i)
Expand Down Expand Up @@ -1522,7 +1522,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
ensure_within_rules_arena(r1.p);
#endif

r2.i = context->matches[r1.s->idx].count;
r2.i = context->matches.entries[r1.s->idx].count;
push(r2);
break;

Expand All @@ -1540,7 +1540,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
ensure_within_rules_arena(r3.p);
#endif

match = context->matches[r3.s->idx].head;
match = context->matches.entries[r3.s->idx].head;
r4.i = 0;

while (match != NULL)
Expand Down Expand Up @@ -1571,7 +1571,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
ensure_within_rules_arena(r2.p);
#endif

match = context->matches[r2.s->idx].head;
match = context->matches.entries[r2.s->idx].head;

i = 1;
r3.i = YR_UNDEFINED;
Expand Down Expand Up @@ -1599,7 +1599,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
ensure_within_rules_arena(r2.p);
#endif

match = context->matches[r2.s->idx].head;
match = context->matches.entries[r2.s->idx].head;

i = 1;
r3.i = YR_UNDEFINED;
Expand Down Expand Up @@ -1629,7 +1629,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
{
if (r2.i == OF_STRING_SET)
{
if (context->matches[r1.s->idx].tail != NULL)
if (context->matches.entries[r1.s->idx].tail != NULL)
{
found++;
}
Expand Down Expand Up @@ -1714,7 +1714,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
#if YR_PARANOID_EXEC
ensure_within_rules_arena(r3.p);
#endif
match = context->matches[r3.s->idx].head;
match = context->matches.entries[r3.s->idx].head;

while (match != NULL)
{
Expand Down Expand Up @@ -1790,7 +1790,7 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
#if YR_PARANOID_EXEC
ensure_within_rules_arena(r1.p);
#endif
match = context->matches[r1.s->idx].head;
match = context->matches.entries[r1.s->idx].head;

while (match != NULL)
{
Expand Down
2 changes: 1 addition & 1 deletion libyara/include/yara/rules.h
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Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
string = STRING_IS_LAST_IN_RULE(string) ? NULL : string + 1)

#define yr_string_matches_foreach(context, string, match) \
for (match = context->matches[string->idx].head; match != NULL; \
for (match = context->matches.entries[string->idx].head; match != NULL; \
match = match->next) \
/* private matches are skipped */ \
if (match->is_private) \
Expand Down
30 changes: 26 additions & 4 deletions libyara/include/yara/types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -172,6 +172,7 @@ typedef struct YR_AC_MATCH YR_AC_MATCH;
typedef struct YR_NAMESPACE YR_NAMESPACE;
typedef struct YR_META YR_META;
typedef struct YR_MATCHES YR_MATCHES;
typedef struct YR_MATCHLIST YR_MATCHLIST;
typedef struct YR_STRING YR_STRING;
typedef struct YR_RULE YR_RULE;
typedef struct YR_RULES YR_RULES;
Expand Down Expand Up @@ -479,6 +480,28 @@ struct YR_MATCHES
YR_MATCH* tail;

int32_t count;

// If true, this YR_MATCHES instance contained a YR_MATCH at some point
// of the scan and will need to be zeroed at the end of the scan.
bool dirty;
};

struct YR_MATCHLIST
{
// Array with pointers to lists of matches. Item N in the array has the
// list of matches for string with index N.
// Total size is equal to length.
YR_MATCHES* entries;

// Array with indices of "dirty" matches, that is, elements in entry that
// must be cleaned before this match list can be reused.
// Total size is equal to length, but only the first dirty_count elements
// are actually valid; all further elements must be ignored.
int32_t* dirty_entries;
int32_t dirty_count;

// Size of this match list
int32_t length;
};

struct YR_MATCH
Expand Down Expand Up @@ -816,17 +839,16 @@ struct YR_SCAN_CONTEXT
// N has too many matches.
YR_BITMASK* strings_temp_disabled;

// Array with pointers to lists of matches. Item N in the array has the
// list of matches for string with index N.
YR_MATCHES* matches;
// A match list containing the matches per string.
YR_MATCHLIST matches;

// "unconfirmed_matches" is like "matches" but for strings that are part of
// a chain. Let's suppose that the string S is split in two chained strings
// S1 <- S2. When a match is found for S1, we can't be sure that S matches
// until a match for S2 is found (within the range defined by chain_gap_min
// and chain_gap_max), so the matches for S1 are put in "unconfirmed_matches"
// until they can be confirmed or discarded.
YR_MATCHES* unconfirmed_matches;
YR_MATCHLIST unconfirmed_matches;

// A bitmap with one bit per rule, bit N is set if the corresponding rule
// must evaluated.
Expand Down
52 changes: 39 additions & 13 deletions libyara/scan.c
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Original file line number Diff line number Diff line change
Expand Up @@ -270,7 +270,7 @@ static void _yr_scan_update_match_chain_length(
if (string->chained_to == NULL)
return;

match = context->unconfirmed_matches[string->chained_to->idx].head;
match = context->unconfirmed_matches.entries[string->chained_to->idx].head;

while (match != NULL)
{
Expand All @@ -289,9 +289,23 @@ static void _yr_scan_update_match_chain_length(

static int _yr_scan_add_match_to_list(
YR_MATCH* match,
YR_MATCHES* matches_list,
YR_MATCHLIST* matchlist,
int string_index,
int replace_if_exists)
{
YR_MATCHES* matches_list = &matchlist->entries[string_index];

// Mark entry as dirty if it is't marked as such yet
if (!matches_list->dirty)
{
matches_list->dirty = true;
// Since dirty_entries has sufficient size for all strings, and
// this one is not marked as dirty and thus not part of dirty_entries yet,
// we can safely add it to dirty_entries without exceeding its maximum size.
matchlist->dirty_entries[matchlist->dirty_count] = string_index;
matchlist->dirty_count++;
}

int result = ERROR_SUCCESS;

#if YR_DEBUG_VERBOSITY > 0
Expand Down Expand Up @@ -369,8 +383,11 @@ _exit:;

static void _yr_scan_remove_match_from_list(
YR_MATCH* match,
YR_MATCHES* matches_list)
YR_MATCHLIST* matchlist,
int string_index)
{
YR_MATCHES* matches_list = &matchlist->entries[string_index];

if (match->prev != NULL)
match->prev->next = match->next;

Expand All @@ -386,6 +403,10 @@ static void _yr_scan_remove_match_from_list(
matches_list->count--;
match->next = NULL;
match->prev = NULL;

// If matches_list->count == 0 now, we could mark this matchlist entry as no longer dirty.
// However, finding and removing the entry from the dirty list takes more time than leaving
// it dirty and (unnecessarily) cleaning it later on, so we don't bother.
}

//
Expand Down Expand Up @@ -449,7 +470,7 @@ static int _yr_scan_verify_chained_string_match(
// list of unconfirmed matches. Unconfirmed matches are sorted in ascending
// offset order. If no unconfirmed match exists, the lowest possible offset
// is the offset of the current match.
match = context->unconfirmed_matches[matching_string->idx].head;
match = context->unconfirmed_matches.entries[matching_string->idx].head;

if (match != NULL)
lowest_offset = match->offset;
Expand All @@ -460,7 +481,7 @@ static int _yr_scan_verify_chained_string_match(
// precedes the currently matching string. If we have a string chain like:
// S1 <- S2 <- S3, and we just found a match for S2, we are iterating the
// list of unconfirmed matches of S1.
match = context->unconfirmed_matches[matching_string->chained_to->idx].head;
match = context->unconfirmed_matches.entries[matching_string->chained_to->idx].head;

while (match != NULL)
{
Expand All @@ -481,7 +502,8 @@ static int _yr_scan_verify_chained_string_match(
// match can't be an actual match)
_yr_scan_remove_match_from_list(
match,
&context->unconfirmed_matches[matching_string->chained_to->idx]);
&context->unconfirmed_matches,
matching_string->chained_to->idx);
}
else if (
ending_offset + matching_string->chain_gap_max >= match_offset &&
Expand Down Expand Up @@ -517,7 +539,7 @@ static int _yr_scan_verify_chained_string_match(
// every unconfirmed match in all the strings in the chain up to the head
// of the chain.
match =
context->unconfirmed_matches[matching_string->chained_to->idx].head;
context->unconfirmed_matches.entries[matching_string->chained_to->idx].head;

while (match != NULL)
{
Expand All @@ -543,7 +565,7 @@ static int _yr_scan_verify_chained_string_match(
}

// "string" points now to the head of the strings chain.
match = context->unconfirmed_matches[string->idx].head;
match = context->unconfirmed_matches.entries[string->idx].head;

// Iterate over the list of unconfirmed matches of the head of the chain,
// and move to the list of confirmed matches those with a chain_length
Expand All @@ -556,7 +578,9 @@ static int _yr_scan_verify_chained_string_match(
if (match->chain_length == full_chain_length)
{
_yr_scan_remove_match_from_list(
match, &context->unconfirmed_matches[string->idx]);
match,
&context->unconfirmed_matches,
string->idx);

match->match_length = (int32_t) (match_offset - match->offset +
match_length);
Expand All @@ -580,7 +604,7 @@ static int _yr_scan_verify_chained_string_match(
yr_bitmask_set(context->required_eval, string->rule_idx);

FAIL_ON_ERROR(_yr_scan_add_match_to_list(
match, &context->matches[string->idx], false));
match, &context->matches, string->idx, false));
}

match = next_match;
Expand Down Expand Up @@ -627,7 +651,8 @@ static int _yr_scan_verify_chained_string_match(
// an actual match until finding the remaining parts of the chain.
FAIL_ON_ERROR(_yr_scan_add_match_to_list(
new_match,
&context->unconfirmed_matches[matching_string->idx],
&context->unconfirmed_matches,
matching_string->idx,
false));
}
}
Expand Down Expand Up @@ -758,7 +783,8 @@ static int _yr_scan_match_callback(

FAIL_ON_ERROR(_yr_scan_add_match_to_list(
new_match,
&callback_args->context->matches[string->idx],
&callback_args->context->matches,
string->idx,
STRING_IS_GREEDY_REGEXP(string)));
}
}
Expand Down Expand Up @@ -1059,7 +1085,7 @@ int yr_scan_verify_match(
return ERROR_SUCCESS;

if (context->flags & SCAN_FLAGS_FAST_MODE && STRING_IS_SINGLE_MATCH(string) &&
context->matches[string->idx].head != NULL)
context->matches.entries[string->idx].head != NULL)
return ERROR_SUCCESS;

if (STRING_IS_FIXED_OFFSET(string) &&
Expand Down
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