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Fix misuse of signed ints in the HAVEGE module #149

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Merged
merged 2 commits into from
Jul 5, 2019
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Fix misuse of signed ints in the HAVEGE module #149

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7846299
Fix misuse of signed ints in the HAVEGE module
gilles-peskine-arm Jun 7, 2019
bc2adf9
Fix minor type choice inconsistency
gilles-peskine-arm Jun 24, 2019
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7 changes: 4 additions & 3 deletions include/mbedtls/havege.h
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@
#endif

#include <stddef.h>
#include <stdint.h>

#define MBEDTLS_HAVEGE_COLLECT_SIZE 1024

Expand All @@ -43,9 +44,9 @@ extern "C" {
*/
typedef struct mbedtls_havege_state
{
int PT1, PT2, offset[2];
int pool[MBEDTLS_HAVEGE_COLLECT_SIZE];
int WALK[8192];
uint32_t PT1, PT2, offset[2];
uint32_t pool[MBEDTLS_HAVEGE_COLLECT_SIZE];
uint32_t WALK[8192];
}
mbedtls_havege_state;

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22 changes: 12 additions & 10 deletions library/havege.c
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Expand Up @@ -38,6 +38,7 @@
#include "mbedtls/timing.h"
#include "mbedtls/platform_util.h"

#include <stdint.h>
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Style: Should we bother to include stdint.h again as we'd have already included it via including havege.h?

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I tend to prefer to include headers for what they define, not for what headers they pull in. According to this style, since havege.c uses uint32_t, it includes stdint.h.

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Is this the convention we use in the rest of Mbed TLS as well? I'm happy to use whatever the library already does.

It's slightly more efficient to not #include a header if you know the types are already available, as they must since the declarations we use from havege.h require it, because the preprocessor doesn't need to read in that file at all. For large projects, and especially on slow filesystems (e.g. Windows, network drives), this can add up to a big savings in compile time. It's not uncommon to have a style that encourages efficiency. (C++ style guides recommending pre-increment operators over post-increment operators in for loops is one example of this.)

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I don't remember that we ever discussed this, and I don't think we're doing or not-doing this with any noticeable consistency.

All our header files have garden-variety include guards. Compilers typically optimize well for that case. In any case, compilation time is the least of our worries. This is not a 100000-file C++ project. Being a security project, we value security, readability and ease of maintenance rather more than runtime performance, let alone build-time performance. Also, if you want to optimize compilation time, the biggest thing by far would be to get rid of cmake!

#include <string.h>

/* ------------------------------------------------------------------------
Expand All @@ -54,7 +55,7 @@
* ------------------------------------------------------------------------
*/

#define SWAP(X,Y) { int *T = (X); (X) = (Y); (Y) = T; }
#define SWAP(X,Y) { uint32_t *T = (X); (X) = (Y); (Y) = T; }

#define TST1_ENTER if( PTEST & 1 ) { PTEST ^= 3; PTEST >>= 1;
#define TST2_ENTER if( PTEST & 1 ) { PTEST ^= 3; PTEST >>= 1;
Expand All @@ -77,7 +78,7 @@
PTX = (PT1 >> 18) & 7; \
PT1 &= 0x1FFF; \
PT2 &= 0x1FFF; \
CLK = (int) mbedtls_timing_hardclock(); \
CLK = (uint32_t) mbedtls_timing_hardclock(); \
\
i = 0; \
A = &WALK[PT1 ]; RES[i++] ^= *A; \
Expand All @@ -100,7 +101,7 @@
\
IN = (*A >> (5)) ^ (*A << (27)) ^ CLK; \
*A = (*B >> (6)) ^ (*B << (26)) ^ CLK; \
*B = IN; CLK = (int) mbedtls_timing_hardclock(); \
*B = IN; CLK = (uint32_t) mbedtls_timing_hardclock(); \
*C = (*C >> (7)) ^ (*C << (25)) ^ CLK; \
*D = (*D >> (8)) ^ (*D << (24)) ^ CLK; \
\
Expand Down Expand Up @@ -158,10 +159,11 @@
*/
static void havege_fill( mbedtls_havege_state *hs )
{
int i, n = 0;
int U1, U2, *A, *B, *C, *D;
int PT1, PT2, *WALK, RES[16];
int PTX, PTY, CLK, PTEST, IN;
size_t n = 0;
size_t i;
uint32_t U1, U2, *A, *B, *C, *D;
uint32_t PT1, PT2, *WALK, RES[16];
uint32_t PTX, PTY, CLK, PTEST, IN;

WALK = hs->WALK;
PT1 = hs->PT1;
Expand Down Expand Up @@ -212,16 +214,16 @@ void mbedtls_havege_free( mbedtls_havege_state *hs )
*/
int mbedtls_havege_random( void *p_rng, unsigned char *buf, size_t len )
{
int val;
uint32_t val;
size_t use_len;
mbedtls_havege_state *hs = (mbedtls_havege_state *) p_rng;
unsigned char *p = buf;

while( len > 0 )
{
use_len = len;
if( use_len > sizeof(int) )
use_len = sizeof(int);
if( use_len > sizeof( val ) )
use_len = sizeof( val );

if( hs->offset[1] >= MBEDTLS_HAVEGE_COLLECT_SIZE )
havege_fill( hs );
Expand Down