hwrng framework does not have a requirement that the all bytes requested need to be provided. By enforcing such a requirement internally, TPM driver can cause unpredictability in latency, as a single tpm_get_random() call can result multiple TPM commands.
Especially, when TCG_TPM2_HMAC is enabled, extra roundtrips could have significant effect to the system latency. Thus, send TPM command only once and return bytes received instead of committing to the number of requested bytes. Cc: David S. Miller <[email protected]> Cc: Herbert Xu <[email protected]> Cc: Eric Biggers <[email protected]> Signed-off-by: Jarkko Sakkinen <[email protected]> --- v7: - Given that hwrng is now only caller for tpm_get_random(), remove the wait parameter. v4: - Fixed grammar mistakes. --- drivers/char/tpm/tpm-interface.c | 28 +++++----------------------- 1 file changed, 5 insertions(+), 23 deletions(-) diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c index d157be738612..677dcef05dfb 100644 --- a/drivers/char/tpm/tpm-interface.c +++ b/drivers/char/tpm/tpm-interface.c @@ -626,10 +626,6 @@ static int tpm2_get_random(struct tpm_chip *chip, u8 *out, size_t max) */ int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max) { - u32 num_bytes = max; - u8 *out_ptr = out; - int retries = 5; - int total = 0; int rc; if (!out || !max || max > TPM_MAX_RNG_DATA) @@ -646,28 +642,14 @@ int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max) rc = tpm2_start_auth_session(chip); if (rc) return rc; - } - - do { - if (chip->flags & TPM_CHIP_FLAG_TPM2) - rc = tpm2_get_random(chip, out_ptr, num_bytes); - else - rc = tpm1_get_random(chip, out_ptr, num_bytes); - - if (rc < 0) - goto err; - - out_ptr += rc; - total += rc; - num_bytes -= rc; - } while (retries-- && total < max); - tpm_put_ops(chip); - return total ? total : -EIO; + rc = tpm2_get_random(chip, out, max); + } else { + rc = tpm1_get_random(chip, out, max); + } -err: tpm_put_ops(chip); - return rc; + return rc != 0 ? rc : -EIO; } EXPORT_SYMBOL_GPL(tpm_get_random); -- 2.39.5
