Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Linus Walleij]

Hi Peng,

thanks for your patch!

On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:

> Use SMC call enable hardware crypto engine
> due to it only be changed in ATF(EL3).
>
> Signed-off-by: Peng Zhou <peng.zhou@mediatek.com>

Unfortunately this commit message is way to short to
understand what is going on, and has a lot of assumed
previous knowledge.

Can you expand the commit message so that anyone
who just know MMC and some SoC basics can understand
what an SMC call and and what ATF(EL3) means?

I assume this some kind of inline encryption?

I think maybe linux-block mailing list need to be involved
because there is certain a Linux standard way of setting
up inline encryption for the block layer.

For example: how is the key to be used derived?
How is the device unlocked in the first place?

If I insert a LUKS encrypted harddrive in a Linux machine
the whole system is pretty much aware of how this should
be handled and everything "just works", I enter a pass
phrase and off it goes. I can use symmetric keys as well.
How is this stuff done for this hardware?

> +       /*
> +        * 1: MSDC_AES_CTL_INIT
> +        * 4: cap_id, no-meaning now
> +        * 1: cfg_id, we choose the second cfg group
> +        */
> +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);

The same as above: these comments assume that everyone
already knows what is going on.

AES encryption requires a key and I don't see the driver
setting up any key. How is the code in this file:
drivers/mmc/core/crypto.c
interacting with your driver?
drivers/mmc/host/cqhci-crypto.c
is used by SDHCI and is quite readable and I see what is going on.
For example it contains functions like:
cqhci_crypto_program_key()
cqhci_crypto_keyslot_program()
cqhci_crypto_clear_keyslot()
cqhci_crypto_keyslot_evict()
cqhci_find_blk_crypto_mode()

MMC_CAP2_CRYPTO is used as a sign that the driver
can do inline encryption, then devm_blk_ksm_init() is called
to initialize a block encryption abstraction with the block layer.
Ops are registered using
struct blk_ksm_ll_ops cqhci_ksm_ops.

This is very straight forward.

But where does all the above happen for this driver?

I get the feeling that some magic is happening in outoftree
patches or in the secure world, and that is not how we do
these things, you have to use the frameworks.

Yours,
Linus Walleij

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Eric Biggers]

On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> Hi Peng,
> 
> thanks for your patch!
> 
> On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:
> 
> > Use SMC call enable hardware crypto engine
> > due to it only be changed in ATF(EL3).
> >
> > Signed-off-by: Peng Zhou <peng.zhou@mediatek.com>
> 
> Unfortunately this commit message is way to short to
> understand what is going on, and has a lot of assumed
> previous knowledge.
> 
> Can you expand the commit message so that anyone
> who just know MMC and some SoC basics can understand
> what an SMC call and and what ATF(EL3) means?
> 
> I assume this some kind of inline encryption?
> 
> I think maybe linux-block mailing list need to be involved
> because there is certain a Linux standard way of setting
> up inline encryption for the block layer.
> 
> For example: how is the key to be used derived?
> How is the device unlocked in the first place?
> 
> If I insert a LUKS encrypted harddrive in a Linux machine
> the whole system is pretty much aware of how this should
> be handled and everything "just works", I enter a pass
> phrase and off it goes. I can use symmetric keys as well.
> How is this stuff done for this hardware?
> 
> > +       /*
> > +        * 1: MSDC_AES_CTL_INIT
> > +        * 4: cap_id, no-meaning now
> > +        * 1: cfg_id, we choose the second cfg group
> > +        */
> > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);
> 
> The same as above: these comments assume that everyone
> already knows what is going on.
> 
> AES encryption requires a key and I don't see the driver
> setting up any key. How is the code in this file:
> drivers/mmc/core/crypto.c
> interacting with your driver?
> drivers/mmc/host/cqhci-crypto.c
> is used by SDHCI and is quite readable and I see what is going on.
> For example it contains functions like:
> cqhci_crypto_program_key()
> cqhci_crypto_keyslot_program()
> cqhci_crypto_clear_keyslot()
> cqhci_crypto_keyslot_evict()
> cqhci_find_blk_crypto_mode()
> 
> MMC_CAP2_CRYPTO is used as a sign that the driver
> can do inline encryption, then devm_blk_ksm_init() is called
> to initialize a block encryption abstraction with the block layer.
> Ops are registered using
> struct blk_ksm_ll_ops cqhci_ksm_ops.
> 
> This is very straight forward.
> 
> But where does all the above happen for this driver?
> 

It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
hardware follows the eMMC standard fairly closely, so Peng's patch series just
sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
couple extra things to actually enable the hardware's crypto support on Mediatek
platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
enable instead of just working as expected, I don't know though.)

The way all this gets used is via the blk-crypto framework
(Documentation/block/inline-encryption.rst), which is used by fscrypt
(ext4 and f2fs encryption).

Peng, if you could explain all this properly in the cover letter, commit
messages, and code comments (where it makes sense), that would be really helpful
for people.  Also please make sure your patch series is in a thread so that
people see it together.

- Eric

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Ulf Hansson]

+ Arnd, Sudeep

On Thu, 11 Mar 2021 at 20:08, Eric Biggers <ebiggers@kernel.org> wrote:
>
> On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> > Hi Peng,
> >
> > thanks for your patch!
> >
> > On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:
> >
> > > Use SMC call enable hardware crypto engine
> > > due to it only be changed in ATF(EL3).
> > >
> > > Signed-off-by: Peng Zhou <peng.zhou@mediatek.com>
> >
> > Unfortunately this commit message is way to short to
> > understand what is going on, and has a lot of assumed
> > previous knowledge.
> >
> > Can you expand the commit message so that anyone
> > who just know MMC and some SoC basics can understand
> > what an SMC call and and what ATF(EL3) means?
> >
> > I assume this some kind of inline encryption?
> >
> > I think maybe linux-block mailing list need to be involved
> > because there is certain a Linux standard way of setting
> > up inline encryption for the block layer.
> >
> > For example: how is the key to be used derived?
> > How is the device unlocked in the first place?
> >
> > If I insert a LUKS encrypted harddrive in a Linux machine
> > the whole system is pretty much aware of how this should
> > be handled and everything "just works", I enter a pass
> > phrase and off it goes. I can use symmetric keys as well.
> > How is this stuff done for this hardware?
> >
> > > +       /*
> > > +        * 1: MSDC_AES_CTL_INIT
> > > +        * 4: cap_id, no-meaning now
> > > +        * 1: cfg_id, we choose the second cfg group
> > > +        */
> > > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);
> >
> > The same as above: these comments assume that everyone
> > already knows what is going on.
> >
> > AES encryption requires a key and I don't see the driver
> > setting up any key. How is the code in this file:
> > drivers/mmc/core/crypto.c
> > interacting with your driver?
> > drivers/mmc/host/cqhci-crypto.c
> > is used by SDHCI and is quite readable and I see what is going on.
> > For example it contains functions like:
> > cqhci_crypto_program_key()
> > cqhci_crypto_keyslot_program()
> > cqhci_crypto_clear_keyslot()
> > cqhci_crypto_keyslot_evict()
> > cqhci_find_blk_crypto_mode()
> >
> > MMC_CAP2_CRYPTO is used as a sign that the driver
> > can do inline encryption, then devm_blk_ksm_init() is called
> > to initialize a block encryption abstraction with the block layer.
> > Ops are registered using
> > struct blk_ksm_ll_ops cqhci_ksm_ops.
> >
> > This is very straight forward.
> >
> > But where does all the above happen for this driver?
> >
>
> It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> hardware follows the eMMC standard fairly closely, so Peng's patch series just
> sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> couple extra things to actually enable the hardware's crypto support on Mediatek
> platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> enable instead of just working as expected, I don't know though.)

As I have probably indicated earlier, I am starting to become more and
more annoyed with these arm_smccc_smc() calls in generic drivers.

As a matter of fact, I think the situation is about to explode. Just
do a "git grep arm_smccc_smc" and you will find that it's not only SoC
specific drivers that call them. In general we want to keep drivers
portable and this is clearly moving in the wrong direction. Or maybe
it's just me being grumpy and having a bad day. :-)

In the Qcom mmc case (drivers/mmc/host/sdhci-msm.c) for eMMC inline
encryption, the arm_smccc_smc() call is slightly better handled as
it's abstracted behind a Qcom specific firmware API. So, sdhci-msm.c
calls qcom_scm_ice_set_key() (implemented in
drivers/firmware/qcom_scm.c) to program a key. I guess we don't have
an abstraction layer that would fit for this case, right?

My point is, when there is no proper abstraction layer to use for the
relevant arm_smccc_smc() call, the Qcom way is fine to me.

In this Mediatek case, it looks slightly different. To me it looks
more like a resource that needs to be turned on/off to enable/disable
the "inline encryption engine". Could it be modeled as phy,
power-rail, clock, pinctrl or perhaps behind a PM domain (where SoC
specific calls makes perfect sense).

Peng can you please elaborate on what goes on behind the
arm_smccc_smc() call, as that would help us to understand what
abstraction layer to pick?

[...]

Kind regards
Uffe

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Arnd Bergmann]

On Fri, Mar 12, 2021 at 10:05 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> On Thu, 11 Mar 2021 at 20:08, Eric Biggers <ebiggers@kernel.org> wrote:
> > On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> >
> > It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> > hardware follows the eMMC standard fairly closely, so Peng's patch series just
> > sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> > couple extra things to actually enable the hardware's crypto support on Mediatek
> > platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> > enable instead of just working as expected, I don't know though.)
>
> As I have probably indicated earlier, I am starting to become more and
> more annoyed with these arm_smccc_smc() calls in generic drivers.
>
> As a matter of fact, I think the situation is about to explode. Just
> do a "git grep arm_smccc_smc" and you will find that it's not only SoC
> specific drivers that call them. In general we want to keep drivers
> portable and this is clearly moving in the wrong direction. Or maybe
> it's just me being grumpy and having a bad day. :-)

I agree, this really does feel underspecified, as there is no way to
actually know which smc interfaces are available, or which ones belong
to a particular driver. Simply calling them is not that different from
using an ioremap() on a hardwired physical address just because you
know where a device is on a given SoC. Or another way of looking at
it is that these are function calls that are arbitrarily moved out from
the kernel into a piece of (usually) closed source software running on
the same chip.

A first step toward managing this better might be to enforce namespaces
of the smc calls, if we can find a way to limit arm_smccc_smc() calls
those that have the first argument defined in a central header file.

        Arnd

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Linus Walleij]

Hi Eric,

thanks for stepping in and clarifying! I get it better now, I though
this was some other encryption scheme "on the side".

There is one worrying thing in the patch still:

On Thu, Mar 11, 2021 at 8:08 PM Eric Biggers <ebiggers@kernel.org> wrote:
> On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> > On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:

> > > +       /*
> > > +        * 1: MSDC_AES_CTL_INIT
> > > +        * 4: cap_id, no-meaning now
> > > +        * 1: cfg_id, we choose the second cfg group
> > > +        */
> > > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);

So MSDC_AES_CTL_INIT. Assumes we are using AES and AES
only I suppose?

> It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> hardware follows the eMMC standard fairly closely, so Peng's patch series just
> sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> couple extra things to actually enable the hardware's crypto support on Mediatek
> platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> enable instead of just working as expected, I don't know though.)

Now I don't know the limitations of cqhci crypto. Clearly it only supports
AES today.

However would the cqhci crypto grow support for any other crypto
like 2Fish or DES and the user request this, then I suppose there is
no way for the MTK driver to announce "uh no I don't do that"?

Or will this cqhci hardware only ever support AES?

Yours,
Linus Walleij

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Eric Biggers]

On Mon, Mar 15, 2021 at 02:41:58PM +0100, Linus Walleij wrote:
> Hi Eric,
> 
> thanks for stepping in and clarifying! I get it better now, I though
> this was some other encryption scheme "on the side".
> 
> There is one worrying thing in the patch still:
> 
> On Thu, Mar 11, 2021 at 8:08 PM Eric Biggers <ebiggers@kernel.org> wrote:
> > On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> > > On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:
> 
> > > > +       /*
> > > > +        * 1: MSDC_AES_CTL_INIT
> > > > +        * 4: cap_id, no-meaning now
> > > > +        * 1: cfg_id, we choose the second cfg group
> > > > +        */
> > > > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > > > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > > > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);
> 
> So MSDC_AES_CTL_INIT. Assumes we are using AES and AES
> only I suppose?
> 
> > It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> > hardware follows the eMMC standard fairly closely, so Peng's patch series just
> > sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> > couple extra things to actually enable the hardware's crypto support on Mediatek
> > platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> > enable instead of just working as expected, I don't know though.)
> 
> Now I don't know the limitations of cqhci crypto. Clearly it only supports
> AES today.
> 
> However would the cqhci crypto grow support for any other crypto
> like 2Fish or DES and the user request this, then I suppose there is
> no way for the MTK driver to announce "uh no I don't do that"?
> 
> Or will this cqhci hardware only ever support AES?

The standard specifies the encryption algorithms that may be supported, and it
specifies that host controllers have a set of crypto capability registers that
list the subset of those algorithms that the hardware actually supports.  See
cqhci_crypto_init() which reads these registers.

If new algorithms get added, the hardware won't declare support for them.
So what you describe won't be a problem.

If, nevertheless, there is broken hardware that declares support for algorithms
it doesn't support, we could work around it using a method in cqhci_host_ops.
That isn't necessary now though.

- Eric

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Ulf Hansson]

On Tue, 16 Mar 2021 at 09:55, Peng.Zhou <peng.zhou@mediatek.com> wrote:
>
> On Fri, 2021-03-12 at 10:05 +0100, Ulf Hansson wrote:
> > + Arnd, Sudeep
> >
> > On Thu, 11 Mar 2021 at 20:08, Eric Biggers <ebiggers@kernel.org> wrote:
> > >
> > > On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> > > > Hi Peng,
> > > >
> > > > thanks for your patch!
> > > >
> > > > On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:
> > > >
> > > > > Use SMC call enable hardware crypto engine
> > > > > due to it only be changed in ATF(EL3).
> > > > >
> > > > > Signed-off-by: Peng Zhou <peng.zhou@mediatek.com>
> > > >
> > > > Unfortunately this commit message is way to short to
> > > > understand what is going on, and has a lot of assumed
> > > > previous knowledge.
> > > >
> > > > Can you expand the commit message so that anyone
> > > > who just know MMC and some SoC basics can understand
> > > > what an SMC call and and what ATF(EL3) means?
> > > >
> > > > I assume this some kind of inline encryption?
> > > >
> > > > I think maybe linux-block mailing list need to be involved
> > > > because there is certain a Linux standard way of setting
> > > > up inline encryption for the block layer.
> > > >
> > > > For example: how is the key to be used derived?
> > > > How is the device unlocked in the first place?
> > > >
> > > > If I insert a LUKS encrypted harddrive in a Linux machine
> > > > the whole system is pretty much aware of how this should
> > > > be handled and everything "just works", I enter a pass
> > > > phrase and off it goes. I can use symmetric keys as well.
> > > > How is this stuff done for this hardware?
> > > >
> > > > > +       /*
> > > > > +        * 1: MSDC_AES_CTL_INIT
> > > > > +        * 4: cap_id, no-meaning now
> > > > > +        * 1: cfg_id, we choose the second cfg group
> > > > > +        */
> > > > > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > > > > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > > > > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);
> > > >
> > > > The same as above: these comments assume that everyone
> > > > already knows what is going on.
> > > >
> > > > AES encryption requires a key and I don't see the driver
> > > > setting up any key. How is the code in this file:
> > > > drivers/mmc/core/crypto.c
> > > > interacting with your driver?
> > > > drivers/mmc/host/cqhci-crypto.c
> > > > is used by SDHCI and is quite readable and I see what is going on.
> > > > For example it contains functions like:
> > > > cqhci_crypto_program_key()
> > > > cqhci_crypto_keyslot_program()
> > > > cqhci_crypto_clear_keyslot()
> > > > cqhci_crypto_keyslot_evict()
> > > > cqhci_find_blk_crypto_mode()
> > > >
> > > > MMC_CAP2_CRYPTO is used as a sign that the driver
> > > > can do inline encryption, then devm_blk_ksm_init() is called
> > > > to initialize a block encryption abstraction with the block layer.
> > > > Ops are registered using
> > > > struct blk_ksm_ll_ops cqhci_ksm_ops.
> > > >
> > > > This is very straight forward.
> > > >
> > > > But where does all the above happen for this driver?
> > > >
> > >
> > > It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> > > hardware follows the eMMC standard fairly closely, so Peng's patch series just
> > > sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> > > couple extra things to actually enable the hardware's crypto support on Mediatek
> > > platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> > > enable instead of just working as expected, I don't know though.)
> >
> > As I have probably indicated earlier, I am starting to become more and
> > more annoyed with these arm_smccc_smc() calls in generic drivers.
> >
> > As a matter of fact, I think the situation is about to explode. Just
> > do a "git grep arm_smccc_smc" and you will find that it's not only SoC
> > specific drivers that call them. In general we want to keep drivers
> > portable and this is clearly moving in the wrong direction. Or maybe
> > it's just me being grumpy and having a bad day. :-)
> >
> > In the Qcom mmc case (drivers/mmc/host/sdhci-msm.c) for eMMC inline
> > encryption, the arm_smccc_smc() call is slightly better handled as
> > it's abstracted behind a Qcom specific firmware API. So, sdhci-msm.c
> > calls qcom_scm_ice_set_key() (implemented in
> > drivers/firmware/qcom_scm.c) to program a key. I guess we don't have
> > an abstraction layer that would fit for this case, right?
> >
> > My point is, when there is no proper abstraction layer to use for the
> > relevant arm_smccc_smc() call, the Qcom way is fine to me.
> >
> > In this Mediatek case, it looks slightly different. To me it looks
> > more like a resource that needs to be turned on/off to enable/disable
> > the "inline encryption engine". Could it be modeled as phy,
> > power-rail, clock, pinctrl or perhaps behind a PM domain (where SoC
> > specific calls makes perfect sense).
> >
> > Peng can you please elaborate on what goes on behind the
> > arm_smccc_smc() call, as that would help us to understand what
> > abstraction layer to pick?
> >
> > [...]
> >
> > Kind regards
> > Uffe
>
> Hi All,
>
> First of all, I appreciated that you are interested in my patch series
> and give me so much significant suggestions! Then, please let me summary
> the detail information about MediaTek eMMC hardware crypto IP.
>
> Before that, as you know, due to I work for MediaTek.inc that means I'm
> as an employee in this mail thread, so I don't give any comment about
> other SoC manufacturers.I will only focus on ours.
>
>
> [Background] Why I upstream this patch series?
> Obiviously, we want to support hardware level file base encryption, file
> encryption had been a mandatory feature in mobile device such as Android
> environment.
>
> A few years ago, we only support software level file encryption, it
> based on the reality of that time:
>  - There is no official encryption specification announced by JEDEC or
> any device manufacturers
>  - File based encryption is not a mandatory feature for mobile devices
>  - Security is not the highest priority thing for our most of Customers
>
> Time can fly and Market requirement is also, hardware level encryption
> functions had been add in our SoCs in soon, because that:
>  - An encryption specification which is widely recognized by device
> manufacturers and SoC manufacturers had been announced. Although it
> doesn't been accepted by JEDEC until now, most of eMMC device
> manufacturers had support it.
>  - Performance, special in low end mobile device, to some extent,
> hardware encryption could reduce some CPU loading,
>  - Almost overnight, Security has became the super star, everyone want
> it, consider the performance (comparing with full disk encryption) and
> flexibility, file based encryption is indispensable.
>
> One more thing, there is no common framework in kernel when our SoCs had
> crypto IP in that time, so we design a special framework in kernel to
> support it. In fact, we had support hardware encryption for several
> years in a special and non-public way.
>
> You'll know the rest, Eric design a common framework that lets SoC
> manufacturers support hardware encryption easier now. That' why we give
> up our own special private way and try to support it.
>
> In fact, at this point in time, we have used this framework(include my
> patch series) in our mobile products with newest Android version for
> almost one year.
>
>
> [Your question] Why we need use SMC call in our driver? or Why our
> crypto hardware IP is not default on?
>
> Yes, MediaTek eMMC crypto hardware IP is default off in current design
> and most important is we only turn it on in ARM exception level 3
> (EL3,the highest security level), that means we can only control it
> under ARM trust firmware (ATF) environment, but kernel space (it's EL2
> in our platform).
>
> I can get your bewilderment: why it's default off and why put it in high
> security level control?

Actually, I don't have an issue with this, at all. Instead, my worries
are about keeping generic drivers portable, which means resources need
to be modelled through proper abstraction layers. SoC specific drivers
are different, they don't necessarily need to cope with this
requirement.

Additionally, to me, it makes perfect sense to allow the crypto IP
block to be powered off, as you would likely waste energy to have it
always powered on, especially when it's not being in use.

So, this boils down to understand what "turn on" crypto hardware IP
actually means? Is it a clock, a phy, a power-rail or perhaps a
combination of things that is turned on for the IP to work? What
happens behind the SMC call?

The answer to this question will help us understand what abstraction
layer we should pick.

[...]

>
> [Your suggestion]
> In general, I agree it, and I will check qcom's solution then try to do
> a firmware layer for our eMMC driver to call.

According to what you have described, I don't think the Qcom solution
is feasible for this case. In your case it's about turning on a
resource and not about programming a key.

I am sure we can find an existing abstraction layer to use, we just
need to agree on which one that makes best sense.

Kind regards
Uffe

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Ulf Hansson]

On Tue, 16 Mar 2021 at 12:22, Peng.Zhou <peng.zhou@mediatek.com> wrote:
>
> On Tue, 2021-03-16 at 11:09 +0100, Ulf Hansson wrote:
> > On Tue, 16 Mar 2021 at 09:55, Peng.Zhou <peng.zhou@mediatek.com> wrote:
> > >
> > > On Fri, 2021-03-12 at 10:05 +0100, Ulf Hansson wrote:
> > > > + Arnd, Sudeep
> > > >
> > > > On Thu, 11 Mar 2021 at 20:08, Eric Biggers <ebiggers@kernel.org> wrote:
> > > > >
> > > > > On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> > > > > > Hi Peng,
> > > > > >
> > > > > > thanks for your patch!
> > > > > >
> > > > > > On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:
> > > > > >
> > > > > > > Use SMC call enable hardware crypto engine
> > > > > > > due to it only be changed in ATF(EL3).
> > > > > > >
> > > > > > > Signed-off-by: Peng Zhou <peng.zhou@mediatek.com>
> > > > > >
> > > > > > Unfortunately this commit message is way to short to
> > > > > > understand what is going on, and has a lot of assumed
> > > > > > previous knowledge.
> > > > > >
> > > > > > Can you expand the commit message so that anyone
> > > > > > who just know MMC and some SoC basics can understand
> > > > > > what an SMC call and and what ATF(EL3) means?
> > > > > >
> > > > > > I assume this some kind of inline encryption?
> > > > > >
> > > > > > I think maybe linux-block mailing list need to be involved
> > > > > > because there is certain a Linux standard way of setting
> > > > > > up inline encryption for the block layer.
> > > > > >
> > > > > > For example: how is the key to be used derived?
> > > > > > How is the device unlocked in the first place?
> > > > > >
> > > > > > If I insert a LUKS encrypted harddrive in a Linux machine
> > > > > > the whole system is pretty much aware of how this should
> > > > > > be handled and everything "just works", I enter a pass
> > > > > > phrase and off it goes. I can use symmetric keys as well.
> > > > > > How is this stuff done for this hardware?
> > > > > >
> > > > > > > +       /*
> > > > > > > +        * 1: MSDC_AES_CTL_INIT
> > > > > > > +        * 4: cap_id, no-meaning now
> > > > > > > +        * 1: cfg_id, we choose the second cfg group
> > > > > > > +        */
> > > > > > > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > > > > > > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > > > > > > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);
> > > > > >
> > > > > > The same as above: these comments assume that everyone
> > > > > > already knows what is going on.
> > > > > >
> > > > > > AES encryption requires a key and I don't see the driver
> > > > > > setting up any key. How is the code in this file:
> > > > > > drivers/mmc/core/crypto.c
> > > > > > interacting with your driver?
> > > > > > drivers/mmc/host/cqhci-crypto.c
> > > > > > is used by SDHCI and is quite readable and I see what is going on.
> > > > > > For example it contains functions like:
> > > > > > cqhci_crypto_program_key()
> > > > > > cqhci_crypto_keyslot_program()
> > > > > > cqhci_crypto_clear_keyslot()
> > > > > > cqhci_crypto_keyslot_evict()
> > > > > > cqhci_find_blk_crypto_mode()
> > > > > >
> > > > > > MMC_CAP2_CRYPTO is used as a sign that the driver
> > > > > > can do inline encryption, then devm_blk_ksm_init() is called
> > > > > > to initialize a block encryption abstraction with the block layer.
> > > > > > Ops are registered using
> > > > > > struct blk_ksm_ll_ops cqhci_ksm_ops.
> > > > > >
> > > > > > This is very straight forward.
> > > > > >
> > > > > > But where does all the above happen for this driver?
> > > > > >
> > > > >
> > > > > It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> > > > > hardware follows the eMMC standard fairly closely, so Peng's patch series just
> > > > > sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> > > > > couple extra things to actually enable the hardware's crypto support on Mediatek
> > > > > platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> > > > > enable instead of just working as expected, I don't know though.)
> > > >
> > > > As I have probably indicated earlier, I am starting to become more and
> > > > more annoyed with these arm_smccc_smc() calls in generic drivers.
> > > >
> > > > As a matter of fact, I think the situation is about to explode. Just
> > > > do a "git grep arm_smccc_smc" and you will find that it's not only SoC
> > > > specific drivers that call them. In general we want to keep drivers
> > > > portable and this is clearly moving in the wrong direction. Or maybe
> > > > it's just me being grumpy and having a bad day. :-)
> > > >
> > > > In the Qcom mmc case (drivers/mmc/host/sdhci-msm.c) for eMMC inline
> > > > encryption, the arm_smccc_smc() call is slightly better handled as
> > > > it's abstracted behind a Qcom specific firmware API. So, sdhci-msm.c
> > > > calls qcom_scm_ice_set_key() (implemented in
> > > > drivers/firmware/qcom_scm.c) to program a key. I guess we don't have
> > > > an abstraction layer that would fit for this case, right?
> > > >
> > > > My point is, when there is no proper abstraction layer to use for the
> > > > relevant arm_smccc_smc() call, the Qcom way is fine to me.
> > > >
> > > > In this Mediatek case, it looks slightly different. To me it looks
> > > > more like a resource that needs to be turned on/off to enable/disable
> > > > the "inline encryption engine". Could it be modeled as phy,
> > > > power-rail, clock, pinctrl or perhaps behind a PM domain (where SoC
> > > > specific calls makes perfect sense).
> > > >
> > > > Peng can you please elaborate on what goes on behind the
> > > > arm_smccc_smc() call, as that would help us to understand what
> > > > abstraction layer to pick?
> > > >
> > > > [...]
> > > >
> > > > Kind regards
> > > > Uffe
> > >
> > > Hi All,
> > >
> > > First of all, I appreciated that you are interested in my patch series
> > > and give me so much significant suggestions! Then, please let me summary
> > > the detail information about MediaTek eMMC hardware crypto IP.
> > >
> > > Before that, as you know, due to I work for MediaTek.inc that means I'm
> > > as an employee in this mail thread, so I don't give any comment about
> > > other SoC manufacturers.I will only focus on ours.
> > >
> > >
> > > [Background] Why I upstream this patch series?
> > > Obiviously, we want to support hardware level file base encryption, file
> > > encryption had been a mandatory feature in mobile device such as Android
> > > environment.
> > >
> > > A few years ago, we only support software level file encryption, it
> > > based on the reality of that time:
> > >  - There is no official encryption specification announced by JEDEC or
> > > any device manufacturers
> > >  - File based encryption is not a mandatory feature for mobile devices
> > >  - Security is not the highest priority thing for our most of Customers
> > >
> > > Time can fly and Market requirement is also, hardware level encryption
> > > functions had been add in our SoCs in soon, because that:
> > >  - An encryption specification which is widely recognized by device
> > > manufacturers and SoC manufacturers had been announced. Although it
> > > doesn't been accepted by JEDEC until now, most of eMMC device
> > > manufacturers had support it.
> > >  - Performance, special in low end mobile device, to some extent,
> > > hardware encryption could reduce some CPU loading,
> > >  - Almost overnight, Security has became the super star, everyone want
> > > it, consider the performance (comparing with full disk encryption) and
> > > flexibility, file based encryption is indispensable.
> > >
> > > One more thing, there is no common framework in kernel when our SoCs had
> > > crypto IP in that time, so we design a special framework in kernel to
> > > support it. In fact, we had support hardware encryption for several
> > > years in a special and non-public way.
> > >
> > > You'll know the rest, Eric design a common framework that lets SoC
> > > manufacturers support hardware encryption easier now. That' why we give
> > > up our own special private way and try to support it.
> > >
> > > In fact, at this point in time, we have used this framework(include my
> > > patch series) in our mobile products with newest Android version for
> > > almost one year.
> > >
> > >
> > > [Your question] Why we need use SMC call in our driver? or Why our
> > > crypto hardware IP is not default on?
> > >
> > > Yes, MediaTek eMMC crypto hardware IP is default off in current design
> > > and most important is we only turn it on in ARM exception level 3
> > > (EL3,the highest security level), that means we can only control it
> > > under ARM trust firmware (ATF) environment, but kernel space (it's EL2
> > > in our platform).
> > >
> > > I can get your bewilderment: why it's default off and why put it in high
> > > security level control?
> >
> > Actually, I don't have an issue with this, at all. Instead, my worries
> > are about keeping generic drivers portable, which means resources need
> > to be modelled through proper abstraction layers. SoC specific drivers
> > are different, they don't necessarily need to cope with this
> > requirement.
> >
> > Additionally, to me, it makes perfect sense to allow the crypto IP
> > block to be powered off, as you would likely waste energy to have it
> > always powered on, especially when it's not being in use.
> >
> > So, this boils down to understand what "turn on" crypto hardware IP
> > actually means? Is it a clock, a phy, a power-rail or perhaps a
> > combination of things that is turned on for the IP to work? What
> > happens behind the SMC call?
> >
> > The answer to this question will help us understand what abstraction
> > layer we should pick.
>
> Hi,
>
> "turn on" crypto hardware IP has no related about clock or power, it
> means:
>
> On: eMMC host encrypt/dencrpt data works normally.
> Off: eMMC host encrypt/dencrpt data works error, although clock and
> power had been enabled. Error is command timeout or bus hang in our
> platforms.
>
> SMC call means write a register of our SoC specific, a bit of a special
> register actually, such as 0 means disable and 1 means enable.

Okay, thanks for clarifying.

It looks like we have a couple of options to support this. I suggest
we consider the two below, but perhaps others (Arnd/Linus?) have
better ideas?

1)
Model the power on/off of the silicon around the crypto HW through a
phy provider driver. The phy provider should then manage the "ice"
clock and the SMC call, through the ->power_on|off() callbacks, while
the mmc driver would act as the consumer of the phy. This would be
rather straightforward to implement, but I guess it can be debated if
this fits as a phy or not.

2)
Another slightly more complicated solution, would be to manage the SMC
call and the "ice" clock through a PM domain (aka genpd provider). As
a matter of fact, we already have a couple of references that use the
genpd infracture like this, as it allows devices to be turned on/off
from SoC specific code, through runtime PM. I wouldn't mind giving you
more pointers to examples for inspirations, if this is the option we
decide to go for.

Kind regards
Uffe

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Linus Walleij]

On Tue, Mar 16, 2021 at 2:56 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:

> It looks like we have a couple of options to support this. I suggest
> we consider the two below, but perhaps others (Arnd/Linus?) have
> better ideas?

Admittedly it's a bit hard to shoehorn this in as it is not a standard
resource (clk, regulator, genpd, reset, gpio...)

There is drivers/soc and then you end up with the same custom
abstraction that qcom is using. The upside to using that
is that we can #ifdef it to static stubs in the .h file if this SoC
is not used, so I would go for that.

See for example qcom_scm_ice_invalidate_key() used from
drivers/firmware/qcom_scm.c, header is at
include/linux/qcom_scm.h and here you find:
#if IS_ENABLED(CONFIG_QCOM_SCM)
and if not, there are some stubs.

Yours,
Linus Walleij

Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Ulf Hansson]

On Mon, 22 Mar 2021 at 14:45, Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Tue, Mar 16, 2021 at 2:56 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> > It looks like we have a couple of options to support this. I suggest
> > we consider the two below, but perhaps others (Arnd/Linus?) have
> > better ideas?
>
> Admittedly it's a bit hard to shoehorn this in as it is not a standard
> resource (clk, regulator, genpd, reset, gpio...)

In my opinion, I wouldn't object if we would model this as phy, simply
because I think it would be the easiest way. Although, I agree, it's
not a perfect fit.

>
> There is drivers/soc and then you end up with the same custom
> abstraction that qcom is using. The upside to using that
> is that we can #ifdef it to static stubs in the .h file if this SoC
> is not used, so I would go for that.
>
> See for example qcom_scm_ice_invalidate_key() used from
> drivers/firmware/qcom_scm.c, header is at
> include/linux/qcom_scm.h and here you find:
> #if IS_ENABLED(CONFIG_QCOM_SCM)
> and if not, there are some stubs.

Please, no. As discussed and also pointed out by Arnd in another
thread, generic drivers must remain portable and must not get
sprinkled with SoC specific code. If not, we would be moving backwards
and increasing the fragmentation of the kernel.

The qcom case is about programming a crypto key, which seems rather
specific to me. I can't figure out another generic way to support
this, but using the SoC specific calls.

The Mediatek case is about turning on/off a resource to activate the
device. If the phy framework doesn't work for us (or another), then at
least we should fall back to use runtime PM + PM domain provider
(genpd), because this would solve the problem. SoC specific code, like
the SMC call can then be called from the genpd provider driver and
abstracted from generic drivers.

Additionally, in this case the mmc driver has already runtime PM
support deployed, which means some of the work has already been
completed.

>
> Yours,
> Linus Walleij

Kind regards
Uffe