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 A85012D6620; Wed, 25 Jun 2025 16:43:11 +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=1750869791; cv=none; b=rTe5e68GD4dh5SjSbbLFTcLrcoZ3b4Mx7JnLIfw0DlkGa5lLbaYK6gDZoWyRuX9o93O2n2EjC1DUBRaTv1GDUfzyXG2HpeuX0v6oHaOwRPyX47MFsJfT+HLGpnQAGROPmit29GuFX10jh82pa5f0VrGuRyoisDhOdDK4CWKS1Ks= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750869791; c=relaxed/simple; bh=cGUv2CNBzq8vRhYQyXdVewQNEc85rFT6i3y9uZ6djqo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KVcIBNDFWZTzQ/WdDJ9ru/Av54CcAkr/Kn4xiHIlzMSrWZl7m9+OM/iz/iPABGLyObsgVrzysqmkCtL5b0ru5gyXeuNAKo5CQFiZJLT0tvVQnQWbIsNasVYPgozq9/BDOFpyb2tW8YIxv0ZL6dHYjWL25/L59FZfc5KQD67BAhE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GIZQoXRj; 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="GIZQoXRj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8898C4CEEA; Wed, 25 Jun 2025 16:43:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750869791; bh=cGUv2CNBzq8vRhYQyXdVewQNEc85rFT6i3y9uZ6djqo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GIZQoXRjPJf7bB9nJwnxXrptTu7KAo3FIQNN/Qx3re80R0ixpmIIcKBYMXjFCjUYA j43xvw+D4pOPKMacA08z8ulicpCdbAd6bTcAGGGEzNPS3c7wJzraRzFRLOLZLP+TrS jTeVaHd0rWrr0EuC8p7EmHgsxw9LDe6eToUPBqLuj8BHWUvnEg2bIcWvCAN9jPAno6 6SoixPbKPkFBb2PHl4RU4FQ98JrfsPd9c4CeyWnTvRBOPq+mYyrETHwXfvnvY/6diA sY2eWe7D5VJ8BPnpwcXRhMPHiGTKqZlbcLGxdTrwCbeZD6q3/4UWeOtORMAL45UzL5 puI38zYxf1UJA== Date: Wed, 25 Jun 2025 19:43:07 +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-kernel@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 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(): /* * Read the chip status bitmask. After completion, the returned will mask will * return value cached at the point of completion up until the next transmit. */ static u8 tpm_chip_status(struct tpm_chip *chip) { u8 status_masked = chip->status & chip->ops_req_complete_mask; if (status_masked == chip->ops->req_complete_val) return chip->status; chip->status = tpm_chip_status(chip); return chip->status; } I think tpm_chip_status() should be the gatekeeper for such event, or like the correct layer of abstraction here ... Then just reset chip->status to zero at the beginning of tpm_try_transmit(). BR, Jarkko