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Multiple volatile variables in a C statement undefined

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Undefined behaviour when there are multiple volatile variables accessed
in the one C statement.
Changes to introduce non-volatile temporaries, split statement or make
variable non-volatile.
This commit is contained in:
Sean Parkinson
2026-01-07 09:44:15 +10:00
parent 2354ea196b
commit 1aa79af41e
4 changed files with 27 additions and 17 deletions
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31
src/internal.c
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@@ -21208,13 +21208,11 @@ static byte MaskMac(const byte* data, int sz, int macSz, byte* expMac)
int i, j;
int r = 0;
unsigned char mac[WC_MAX_DIGEST_SIZE];
volatile int scanStart = sz - 1 - TLS_MAX_PAD_SZ - macSz;
int scanStart = sz - 1 - TLS_MAX_PAD_SZ - macSz;
volatile int macEnd = sz - 1 - data[sz - 1];
volatile int macStart = macEnd - macSz;
int macStart = macEnd - macSz;
volatile int maskScanStart;
volatile int maskMacStart;
volatile unsigned char started;
volatile unsigned char notEnded;
unsigned char good = 0;
maskScanStart = ctMaskIntGTE(scanStart, 0);
@@ -21224,22 +21222,31 @@ static byte MaskMac(const byte* data, int sz, int macSz, byte* expMac)
/* Div on Intel has different speeds depending on value.
* Use a bitwise AND or mod a specific value (converted to mul). */
if ((macSz & (macSz - 1)) == 0)
r = (macSz - (scanStart - macStart)) & (macSz - 1);
if ((macSz & (macSz - 1)) == 0) {
r = macSz - scanStart;
r += macStart;
r &= (macSz - 1);
}
#ifndef NO_SHA
else if (macSz == WC_SHA_DIGEST_SIZE)
r = (macSz - (scanStart - macStart)) % WC_SHA_DIGEST_SIZE;
else if (macSz == WC_SHA_DIGEST_SIZE) {
r = macSz - scanStart;
r += macStart;
r %= WC_SHA_DIGEST_SIZE;
}
#endif
#ifdef WOLFSSL_SHA384
else if (macSz == WC_SHA384_DIGEST_SIZE)
r = (macSz - (scanStart - macStart)) % WC_SHA384_DIGEST_SIZE;
else if (macSz == WC_SHA384_DIGEST_SIZE) {
r = macSz - scanStart;
r += macStart;
r %= WC_SHA384_DIGEST_SIZE;
}
#endif
XMEMSET(mac, 0, (size_t)(macSz));
for (i = scanStart; i < sz; i += macSz) {
for (j = 0; j < macSz && j + i < sz; j++) {
started = ctMaskGTE(i + j, macStart);
notEnded = ctMaskLT(i + j, macEnd);
unsigned char started = ctMaskGTE(i + j, macStart);
unsigned char notEnded = ctMaskLT(i + j, macEnd);
mac[j] |= started & notEnded & data[i + j];
}
}