6.15-stable review patch. If anyone has any objections, please let me know.
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From: Jarkko Sakkinen jarkko@kernel.org
[ Upstream commit d4640c394f23b202a89512346cf28f6622a49031 ]
The current implementation of timeout detection works in the following way:
1. Read completion status. If completed, return the data 2. Sleep for some time (usleep_range) 3. Check for timeout using current jiffies value. Return an error if timed out 4. Goto 1
usleep_range doesn't guarantee it's always going to wake up strictly in (min, max) range, so such a situation is possible:
1. Driver reads completion status. No completion yet 2. Process sleeps indefinitely. In the meantime, TPM responds 3. We check for timeout without checking for the completion again. Result is lost.
Such a situation also happens for the guest VMs: if vCPU goes to sleep and doesn't get scheduled for some time, the guest TPM driver will timeout instantly after waking up without checking for the completion (which may already be in place).
Perform the completion check once again after exiting the busy loop in order to give the device the last chance to send us some data.
Since now we check for completion in two places, extract this check into a separate function.
Signed-off-by: Ivan Orlov ivan.orlov0322@gmail.com Reviewed-by: Jonathan McDowell noodles@meta.com Signed-off-by: Jarkko Sakkinen jarkko@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/char/tpm/tpm-interface.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c index 8d7e4da6ed53..8d18b33aa62d 100644 --- a/drivers/char/tpm/tpm-interface.c +++ b/drivers/char/tpm/tpm-interface.c @@ -82,6 +82,13 @@ static bool tpm_chip_req_canceled(struct tpm_chip *chip, u8 status) return chip->ops->req_canceled(chip, status); }
+static bool tpm_transmit_completed(u8 status, struct tpm_chip *chip) +{ + u8 status_masked = status & chip->ops->req_complete_mask; + + return status_masked == chip->ops->req_complete_val; +} + static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz) { struct tpm_header *header = buf; @@ -129,8 +136,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz) stop = jiffies + tpm_calc_ordinal_duration(chip, ordinal); do { u8 status = tpm_chip_status(chip); - if ((status & chip->ops->req_complete_mask) == - chip->ops->req_complete_val) + if (tpm_transmit_completed(status, chip)) goto out_recv;
if (tpm_chip_req_canceled(chip, status)) { @@ -142,6 +148,13 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz) rmb(); } while (time_before(jiffies, stop));
+ /* + * Check for completion one more time, just in case the device reported + * it while the driver was sleeping in the busy loop above. + */ + if (tpm_transmit_completed(tpm_chip_status(chip), chip)) + goto out_recv; + tpm_chip_cancel(chip); dev_err(&chip->dev, "Operation Timed out\n"); return -ETIME;