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Fix swtpm UART read timeout to keep waiting until cumulative limit #660

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Fix swtpm UART read timeout to keep waiting until cumulative limit #660

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26 changes: 19 additions & 7 deletions src/tpm2_swtpm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -74,10 +74,12 @@
#ifndef O_NOFOLLOW
#define O_NOFOLLOW 0
#endif
/* Cumulative wall-clock timeout for SwTpmReceive. Defends against trickle
* senders that repeatedly reset the per-read VMIN/VTIME timer. */
/* Cumulative wall-clock timeout for SwTpmReceive. Bounds the total wait for
* a response, which can exceed one VTIME period (e.g. RSA key generation on
* an MCU), and defends against trickle senders that repeatedly reset the
* per-read VMIN/VTIME timer. */
#ifndef WOLFTPM_SWTPM_UART_RX_TIMEOUT_SECS
#define WOLFTPM_SWTPM_UART_RX_TIMEOUT_SECS 30
#define WOLFTPM_SWTPM_UART_RX_TIMEOUT_SECS 60
#endif
#endif

Expand Down Expand Up @@ -217,6 +219,16 @@ static TPM_RC SwTpmReceive(TPM2_CTX* ctx, void* buffer, size_t rxSz)
rc = TPM_RC_FAILURE;
break;
}
#if defined(WOLFTPM_SWTPM_UART) && defined(CLOCK_MONOTONIC)
/* A zero-byte TTY read means VTIME expired, not EOF: keep waiting
* until the cumulative timeout */
if (wrc == 0 && haveStart &&
clock_gettime(CLOCK_MONOTONIC, &now) == 0 &&
(now.tv_sec - start.tv_sec) <=
WOLFTPM_SWTPM_UART_RX_TIMEOUT_SECS) {
continue;
}
#endif
if (wrc == 0) {
#ifdef DEBUG_WOLFTPM
printf("Failed to read from TPM socket: EOF\n");
Expand Down Expand Up @@ -359,10 +371,10 @@ static TPM_RC SwTpmConnect(TPM2_CTX* ctx, const char* host, const char* port)
tty.c_oflag &= ~OPOST;
tty.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);

/* Read with overall timeout.
* RSA key generation on embedded targets can take 10+ seconds,
* so use a generous timeout. With VMIN=0 and VTIME>0, read()
* returns after the timeout even if no byte is received. */
/* Read with per-read timeout. With VMIN=0 and VTIME>0, read() returns
* after the timeout even if no byte is received; SwTpmReceive keeps
* waiting up to WOLFTPM_SWTPM_UART_RX_TIMEOUT_SECS, since RSA key
* generation on embedded targets can take longer than one period. */
tty.c_cc[VMIN] = 0; /* allow timeout without requiring first byte */
tty.c_cc[VTIME] = 200; /* 20 second timeout (tenths of seconds) */

Expand Down
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