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XOR Values. #1745

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merged 2 commits into from
Jul 21, 2022
Merged

XOR Values. #1745

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59c58e8
XOR Values.
wxsBSD Jul 6, 2022
88f8c02
xor key fixes.
wxsBSD Jul 14, 2022
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12 changes: 11 additions & 1 deletion cli/yara.c
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Original file line number Diff line number Diff line change
Expand Up @@ -147,6 +147,7 @@ static bool show_tags = false;
static bool show_stats = false;
static bool show_strings = false;
static bool show_string_length = false;
static bool show_xor_key = false;
static bool show_meta = false;
static bool show_namespace = false;
static bool show_version = false;
Expand Down Expand Up @@ -296,6 +297,12 @@ args_option_t options[] = {
&show_string_length,
_T("print length of matched strings")),

OPT_BOOLEAN(
'X',
_T("print-xor-key"),
&show_xor_key,
_T("print xor key of matched strings")),

OPT_BOOLEAN('g', _T("print-tags"), &show_tags, _T("print tags")),

OPT_BOOLEAN(
Expand Down Expand Up @@ -1081,7 +1088,7 @@ static int handle_message(

// Show matched strings.

if (show_strings || show_string_length)
if (show_strings || show_string_length || show_xor_key)
{
YR_STRING* string;

Expand All @@ -1103,6 +1110,9 @@ static int handle_message(
match->base + match->offset,
string->identifier);

if (show_xor_key)
_tprintf(_T(":xor(0x%02x)"), match->xor_key);

if (show_strings)
{
_tprintf(_T(": "));
Expand Down
3 changes: 3 additions & 0 deletions libyara/include/yara/types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -496,6 +496,9 @@ struct YR_MATCH

// True if this is match for a private string.
bool is_private;

// Set to the xor key if this is an xor string.
uint8_t xor_key;
};

struct YR_AC_STATE
Expand Down
42 changes: 35 additions & 7 deletions libyara/scan.c
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Original file line number Diff line number Diff line change
Expand Up @@ -55,14 +55,16 @@ typedef struct _CALLBACK_ARGS

int forward_matches;
int full_word;
int xor_key;

} CALLBACK_ARGS;

static int _yr_scan_xor_compare(
const uint8_t* data,
size_t data_size,
uint8_t* string,
size_t string_length)
size_t string_length,
uint8_t* xor_key)
{
int result = 0;
const uint8_t* s1 = data;
Expand Down Expand Up @@ -94,15 +96,20 @@ _exit:;
string_length,
result);

if (result > 0)
*xor_key = k;

return result;
}

static int _yr_scan_xor_wcompare(
const uint8_t* data,
size_t data_size,
uint8_t* string,
size_t string_length)
size_t string_length,
uint8_t* xor_key)
{
int result = 0;
const uint8_t* s1 = data;
const uint8_t* s2 = string;
uint8_t k = 0;
Expand All @@ -124,7 +131,12 @@ static int _yr_scan_xor_wcompare(
i++;
}

return (int) ((i == string_length) ? i * 2 : 0);
result = (int) ((i == string_length) ? i * 2 : 0);

if (result > 0)
*xor_key = k;

return result;
}

static int _yr_scan_compare(
Expand Down Expand Up @@ -397,7 +409,8 @@ static int _yr_scan_verify_chained_string_match(
const uint8_t* match_data,
uint64_t match_base,
uint64_t match_offset,
int32_t match_length)
int32_t match_length,
uint8_t xor_key)
{
YR_DEBUG_FPRINTF(
2,
Expand Down Expand Up @@ -584,6 +597,7 @@ static int _yr_scan_verify_chained_string_match(
new_match->prev = NULL;
new_match->next = NULL;
new_match->is_private = STRING_IS_PRIVATE(matching_string);
new_match->xor_key = xor_key;

// A copy of the matching data is written to the matches_arena, the
// amount of data copies is limited by YR_CONFIG_MAX_MATCH_DATA.
Expand Down Expand Up @@ -687,7 +701,8 @@ static int _yr_scan_match_callback(
match_data,
callback_args->data_base,
match_offset,
match_length);
match_length,
callback_args->xor_key);
}
else
{
Expand Down Expand Up @@ -733,6 +748,7 @@ static int _yr_scan_match_callback(
new_match->prev = NULL;
new_match->next = NULL;
new_match->is_private = STRING_IS_PRIVATE(string);
new_match->xor_key = callback_args->xor_key;

FAIL_ON_ERROR(_yr_scan_add_match_to_list(
new_match,
Expand Down Expand Up @@ -843,6 +859,8 @@ static int _yr_scan_verify_re_match(
callback_args.data_base = data_base;
callback_args.forward_matches = forward_matches;
callback_args.full_word = STRING_IS_FULL_WORD(ac_match->string);
// xor modifier is not valid for RE but set it so we don't leak stack values.
callback_args.xor_key = 0;

if (ac_match->backward_code != NULL)
{
Expand Down Expand Up @@ -886,6 +904,7 @@ static int _yr_scan_verify_literal_match(

int flags = 0;
int forward_matches = 0;
uint8_t xor_key = 0;

CALLBACK_ARGS callback_args;
YR_STRING* string = ac_match->string;
Expand Down Expand Up @@ -927,13 +946,21 @@ static int _yr_scan_verify_literal_match(
if (STRING_IS_WIDE(string))
{
forward_matches = _yr_scan_xor_wcompare(
data + offset, data_size - offset, string->string, string->length);
data + offset,
data_size - offset,
string->string,
string->length,
&xor_key);
}

if (forward_matches == 0)
{
forward_matches = _yr_scan_xor_compare(
data + offset, data_size - offset, string->string, string->length);
data + offset,
data_size - offset,
string->string,
string->length,
&xor_key);
}
}
}
Expand All @@ -954,6 +981,7 @@ static int _yr_scan_verify_literal_match(
callback_args.data_base = data_base;
callback_args.forward_matches = forward_matches;
callback_args.full_word = STRING_IS_FULL_WORD(string);
callback_args.xor_key = xor_key;

FAIL_ON_ERROR(
_yr_scan_match_callback(data + offset, 0, flags, &callback_args));
Expand Down