From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F311010942; Fri, 4 Jul 2025 15:16:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751642177; cv=none; b=RBiQCWmiYAa7r/RjsaBGiYEAETwT4AMsUgfMz68nJYEaIX/cNyxq5ExOEgDpPEfjWj0ga0iBLnBt00kA5qvKGrvemQDMcWl/Uf7i2r8MaWGi6p8rJaOAzn9l6awt0n/XaiIOs27iQyrJqPyNNoLqavZK1OvPC1SSlw1kPamBkyA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751642177; c=relaxed/simple; bh=fdncFe+kRLkLN8JKby0Zgs6+T99Ms/eQIw5jZsqT9Ys=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XNUetQEqIqYmpN8uMOOjsXs8RV22fr0jiFIfxtPnEUG5nvPkuD1Wdsn8u94VpAMf/lMq/Qw/gGCfyfJuk6SfG5zTNNBk8q9xhGEUxiZMj299y5P6RsLEtC1WRhBYZfCt4H6eA26BA1RTcSE3iy+lV28KlHTFzUT2jNJPYmbzZfQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=N2OUUvjM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="N2OUUvjM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73289C4CEE3; Fri, 4 Jul 2025 15:16:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1751642176; bh=fdncFe+kRLkLN8JKby0Zgs6+T99Ms/eQIw5jZsqT9Ys=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=N2OUUvjMt2UqsDufh8VcCyObOPhay8lZQM3h1uFbdqHCFtkKcWgi6Gnl8J0DI8qPC G5c6/M+LtmppkfVtj2PrpCzSI9ysYowncS7Cg5/ZyFxrRxkm9qfEOwaegiYBdEvjJN /g8n/39NKKy2HEvbXjUOo6uIyT4gi73ds2GUTHAhR1K0NlzXdz3pLD9mLTCKwpFYzT ZgarzHmuS1vFs8ZkOxXw2oP6zSyRKf9viUMhEv/A5y28r5WQcealVVksLSqpJhEGWr Ay3MoeBIMY4NF/p94veWNytGWNdZKaAlc7vVnRRTrl5WQ4iIlDOd6jvycPSOfgzJ5E zHJATaoA5UIuQ== Date: Fri, 4 Jul 2025 18:16:13 +0300 From: Jarkko Sakkinen To: Jonathan McDowell Cc: "Orlov, Ivan" , "peterhuewe@gmx.de" , "jgg@ziepe.ca" , "linux-integrity@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Woodhouse, David" Subject: Re: [PATCH v2] tpm: Fix the timeout & use ktime Message-ID: References: <20250620180828.98413-1-iorlov@amazon.com> Precedence: bulk X-Mailing-List: linux-integrity@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jul 04, 2025 at 10:02:33AM +0100, Jonathan McDowell wrote: > On Wed, Jun 25, 2025 at 07:43:07PM +0300, Jarkko Sakkinen wrote: > > On Sun, Jun 22, 2025 at 09:52:58PM +0100, Jonathan McDowell wrote: > > > On Fri, Jun 20, 2025 at 06:08:31PM +0000, Orlov, Ivan wrote: > > > > 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 > > > > --- > > > > V1 -> V2: > > > > - Exclude the jiffies -> ktime change from the patch > > > > - Instead of recording the time before checking for completion, check > > > > for completion once again after leaving the loop > > > > > > > > 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..6960ee2798e1 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(struct tpm_chip *chip) > > > > +{ > > > > + u8 status_masked = tpm_chip_status(chip) & 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(chip)) > > > > goto out_recv; > > > > > > The only thing I'd point out here is we end up doing a double status read > > > one after the other (once here, once in tpm_transmit_completed), and I'm > > > pretty sure I've seen instances where that caused a problem. > > > > It would be easy to to prevent at least double reads after completion > > e.g., in tpm_chip_status(): > > Or just take the simple approach and make the check after the while loop: > > if ((tpm_chip_status(chip) & chip->ops->req_complete_mask) == > chip->ops->req_complete_val) > goto out_recv; > > There might be potential for a longer term cleanup using chip->status to > cache things, but I'm little concerned that's going to open paths where we > might not correctly update it, so I think it should be a separate piece. > > (I'm motivated by the fact we've started to see the "Operation Canceled" > error and I'd like us to close on the best way to fix it. :) ) This would work for me too! Please send a new version if you feel like it but next week I won't be reviewing that as I'm on holiday. > > J. > -- > I am afraid of the dark. BR, Jarkko