From: Jarkko Sakkinen <jarkko@kernel.org>
To: Hao Wu <hao.wu@rubrik.com>
Cc: Shrihari Kalkar <shrihari.kalkar@rubrik.com>,
Seungyeop Han <seungyeop.han@rubrik.com>,
Anish Jhaveri <anish.jhaveri@rubrik.com>,
peterhuewe@gmx.de, jgg@ziepe.ca, linux-integrity@vger.kernel.org,
Paul Menzel <pmenzel@molgen.mpg.de>,
Ken Goldman <kgold@linux.ibm.com>,
zohar@linux.vnet.ibm.com, why2jjj.linux@gmail.com,
Hamza Attak <hamza@hpe.com>,
gregkh@linuxfoundation.org, arnd@arndb.de,
Nayna <nayna@linux.vnet.ibm.com>,
James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH] tpm: fix ATMEL TPM crash caused by too frequent queries
Date: Mon, 5 Jul 2021 08:19:55 +0300 [thread overview]
Message-ID: <20210705051955.53zoge4rkeocmfyr@kernel.org> (raw)
In-Reply-To: <AB80469F-821A-45D0-878C-7ED97C8B44BF@rubrik.com>
On Fri, Jul 02, 2021 at 12:16:12PM -0700, Hao Wu wrote:
>
> > On Jul 2, 2021, at 4:57 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >
> > On Fri, Jul 02, 2021 at 11:42:39AM +0300, Jarkko Sakkinen wrote:
> >> On Fri, Jul 02, 2021 at 12:59:18AM -0700, Hao Wu wrote:
> >>>> On Jul 2, 2021, at 12:45 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >>>>
> >>>> On Fri, Jul 02, 2021 at 12:33:15AM -0700, Hao Wu wrote:
> >>>>>
> >>>>>
> >>>>>> On Jul 1, 2021, at 11:35 PM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >>>>>>
> >>>>>> On Tue, Jun 29, 2021 at 09:22:05PM -0700, Hao Wu wrote:
> >>>>>>> This is a fix for the ATMEL TPM crash bug reported in
> >>>>>>> https://patchwork.kernel.org/project/linux-integrity/patch/20200926223150.109645-1-hao.wu@rubrik.com/
> >>>>>>>
> >>>>>>> According to the discussions in the original thread,
> >>>>>>> we don't want to revert the timeout of wait_for_tpm_stat
> >>>>>>> for non-ATMEL chips, which brings back the performance cost.
> >>>>>>> For investigation and analysis of why wait_for_tpm_stat
> >>>>>>> caused the issue, and how the regression was introduced,
> >>>>>>> please read the original thread above.
> >>>>>>>
> >>>>>>> Thus the proposed fix here is to only revert the timeout
> >>>>>>> for ATMEL chips by checking the vendor ID.
> >>>>>>>
> >>>>>>> Signed-off-by: Hao Wu <hao.wu@rubrik.com>
> >>>>>>> Fixes: 9f3fc7bcddcb ("tpm: replace msleep() with usleep_range() in TPM 1.2/2.0 generic drivers")
> >>>>>>
> >>>>>> Fixes tag should be before SOB.
> >>>>>>
> >>>>>>> ---
> >>>>>>> Test Plan:
> >>>>>>> - Run fixed kernel with ATMEL TPM chips and see crash
> >>>>>>> has been fixed.
> >>>>>>> - Run fixed kernel with non-ATMEL TPM chips, and confirm
> >>>>>>> the timeout has not been changed.
> >>>>>>>
> >>>>>>> drivers/char/tpm/tpm.h | 9 ++++++++-
> >>>>>>> drivers/char/tpm/tpm_tis_core.c | 19 +++++++++++++++++--
> >>>>>>> include/linux/tpm.h | 2 ++
> >>>>>>> 3 files changed, 27 insertions(+), 3 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> >>>>>>> index 283f78211c3a..bc6aa7f9e119 100644
> >>>>>>> --- a/drivers/char/tpm/tpm.h
> >>>>>>> +++ b/drivers/char/tpm/tpm.h
> >>>>>>> @@ -42,7 +42,9 @@ enum tpm_timeout {
> >>>>>>> TPM_TIMEOUT_RANGE_US = 300, /* usecs */
> >>>>>>> TPM_TIMEOUT_POLL = 1, /* msecs */
> >>>>>>> TPM_TIMEOUT_USECS_MIN = 100, /* usecs */
> >>>>>>> - TPM_TIMEOUT_USECS_MAX = 500 /* usecs */
> >>>>>>> + TPM_TIMEOUT_USECS_MAX = 500, /* usecs */
> >>>>>>
> >>>>>> What is this change?
> >>>>> Need to add the tailing comma
> >>>>>
> >>>>>>
> >>>>>>> + TPM_TIMEOUT_WAIT_STAT = 500, /* usecs */
> >>>>>>> + TPM_ATML_TIMEOUT_WAIT_STAT = 15000 /* usecs */
> >>>>>>> };
> >>>>>>>
> >>>>>>> /* TPM addresses */
> >>>>>>> @@ -189,6 +191,11 @@ static inline void tpm_msleep(unsigned int delay_msec)
> >>>>>>> delay_msec * 1000);
> >>>>>>> };
> >>>>>>>
> >>>>>>> +static inline void tpm_usleep(unsigned int delay_usec)
> >>>>>>> +{
> >>>>>>> + usleep_range(delay_usec - TPM_TIMEOUT_RANGE_US, delay_usec);
> >>>>>>> +};
> >>>>>>
> >>>>>> Please remove this, and open code.
> >>>>> Ok, will do
> >>>>>
> >>>>>>> +
> >>>>>>> int tpm_chip_start(struct tpm_chip *chip);
> >>>>>>> void tpm_chip_stop(struct tpm_chip *chip);
> >>>>>>> struct tpm_chip *tpm_find_get_ops(struct tpm_chip *chip);
> >>>>>>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> >>>>>>> index 55b9d3965ae1..9ddd4edfe1c2 100644
> >>>>>>> --- a/drivers/char/tpm/tpm_tis_core.c
> >>>>>>> +++ b/drivers/char/tpm/tpm_tis_core.c
> >>>>>>> @@ -80,8 +80,12 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
> >>>>>>> }
> >>>>>>> } else {
> >>>>>>> do {
> >>>>>>> - usleep_range(TPM_TIMEOUT_USECS_MIN,
> >>>>>>> - TPM_TIMEOUT_USECS_MAX);
> >>>>>>> + if (chip->timeout_wait_stat &&
> >>>>>>> + chip->timeout_wait_stat >= TPM_TIMEOUT_WAIT_STAT) {
> >>>>>>> + tpm_usleep((unsigned int)(chip->timeout_wait_stat));
> >>>>>>> + } else {
> >>>>>>> + tpm_usleep((unsigned int)(TPM_TIMEOUT_WAIT_STAT));
> >>>>>>> + }
> >>>>>>
> >>>>>> Invalid use of braces. Please read
> >>>>>>
> >>>>>> https://www.kernel.org/doc/html/v5.13/process/coding-style.html
> >>>>>>
> >>>>>> Why do you have to use this field conditionally anyway? Why doesn't
> >>>>>> it always contain a legit value?
> >>>>> The field is legit now, but doesn’t hurt to do addition check for robustness
> >>>>> to ensure no crash ? Just in case the value is updated below TPM_TIMEOUT_WAIT_STAT ?
> >>>>>
> >>>>> Can remove if we think it is not needed.
> >>>>
> >>>> A simple question: why you use it conditionally? Can the field contain invalid value?
> >>>>
> >>> There are two checks
> >>> - chip->timeout_wait_stat >= TPM_TIMEOUT_WAIT_STAT
> >>> It could be invalid when future developer set it to some value less than `TPM_TIMEOUT_USECS_MIN`,
> >>> and crash the usleep
> >>
> >> I don't understand this. Why you don't set to appropriate value?
> Ok, fair enough, I assume developers will test it anyway to ensure no crash. Will remove this check.
>
> > What you should do, is to define two fields:
> >
> > - tpm_timeout_min
> > - tpm_timeout_max
> >
> > And initialize these to TPM_TIMEOUT_USECS_MIN and TPM_TIMEOUT_USECS_MAX.
> >
> > Then fixup those for Atmel (with a simple if-statement, switch-case is
> > overkill).
> Switch was more for extensibility when other vendor has similar issue,
> but we can refactor when needed in the future. I can use if-statement for now.
Make things more fancy *only* when you actually need more fancy.
> > The way you work out things right now is broken:
> >
> > 1. Before for non-Atmel: usleep_range(100, 500)
> > 2. After for non-Atmel: usleep_range(200, 500)
> I realized this in day-1, I think this range change does not matter much.
By saying that you are actually saying that *undocumented* semantic changes
to the kernel code are fine as long as they don't change things "too much"
Are you serious about this?
> `TPM_TIMEOUT_RANGE_US=300` is already used in the codebase, I assume people define
> such if for general use cases for usleep_range in TPM
> But we can add two fields if that makes us more comfortable to strictly follow the current code
> semantically.
This has absolutely nothing to do with "comfortable". It's black and white
wrong.
/Jarkko
next prev parent reply other threads:[~2021-07-05 5:19 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-20 23:18 [PATCH] Fix Atmel TPM crash caused by too frequent queries Hao Wu
2021-06-23 13:35 ` Jarkko Sakkinen
2021-06-24 5:49 ` Hao Wu
2021-06-29 20:06 ` Jarkko Sakkinen
2021-06-30 4:27 ` Hao Wu
2021-06-24 5:33 ` Hao Wu
2021-06-29 20:07 ` Jarkko Sakkinen
2021-06-30 4:22 ` [PATCH] tpm: fix ATMEL " Hao Wu
2021-07-02 6:35 ` Jarkko Sakkinen
2021-07-02 7:12 ` Greg KH
2021-07-02 7:33 ` Hao Wu
2021-07-02 7:35 ` Hao Wu
2021-07-02 7:45 ` Jarkko Sakkinen
2021-07-02 7:59 ` Hao Wu
2021-07-02 8:42 ` Jarkko Sakkinen
2021-07-02 11:57 ` Jarkko Sakkinen
2021-07-02 19:16 ` Hao Wu
2021-07-05 5:19 ` Jarkko Sakkinen [this message]
2021-07-05 5:29 ` Hao Wu
2021-07-04 0:07 ` Hao Wu
2021-07-05 7:15 ` Jarkko Sakkinen
2021-07-05 23:09 ` Hao Wu
2021-07-06 12:34 ` Mimi Zohar
2021-07-07 4:18 ` Hao Wu
2021-07-07 4:34 ` Hao Wu
2021-07-07 4:31 ` [PATCH v2] " Hao Wu
2021-07-07 9:24 ` Jarkko Sakkinen
2021-07-07 18:28 ` Hao Wu
2021-07-07 21:10 ` Jarkko Sakkinen
2021-07-09 4:43 ` Hao Wu
2021-07-09 4:40 ` [PATCH v2] tpm: fix Atmel " Hao Wu
2021-07-09 17:47 ` Jarkko Sakkinen
2021-07-09 19:23 ` Hao Wu
2021-07-11 7:37 ` Hao Wu
2021-07-16 5:30 ` Hao Wu
2021-07-11 7:51 ` [PATCH v3] " Hao Wu
2021-07-27 2:46 ` Jarkko Sakkinen
2021-07-27 3:40 ` Hao Wu
2021-08-14 22:25 ` [PATCH v4] " Hao Wu
2021-08-26 5:38 ` Hao Wu
2021-08-26 16:24 ` Jarkko Sakkinen
2021-08-27 0:35 ` Hao Wu
2021-09-04 21:14 ` Hao Wu
2021-09-04 23:15 ` Hao Wu
2021-09-05 3:51 ` [PATCH v5] " Hao Wu
2021-09-07 17:43 ` Jarkko Sakkinen
2021-09-08 8:33 ` Hao Wu
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