From: Dan Williams <hidden> Date: 2021-08-24 01:06:04
On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan
[off-list ref] wrote:
On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:
quoted
quoted
Add a new variant of pci_iomap for mapping all PCI resources
of a devices as shared memory with a hypervisor in a confidential
guest.
Signed-off-by: Andi Kleen<redacted>
Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@linux.intel.com>
I'm a bit puzzled by this part. So why should the guest*not* map
pci memory as shared? And if the answer is never (as it seems to be)
then why not just make regular pci_iomap DTRT?
It is in the context of confidential guest (where VMM is un-trusted). So
we don't want to make all PCI resource as shared. It should be allowed
only for hardened drivers/devices.
That's confusing, isn't device authorization what keeps unaudited
drivers from loading against untrusted devices? I'm feeling like
Michael that this should be a detail that drivers need not care about
explicitly, in which case it does not need to be exported because the
detail can be buried in lower levels.
Note, I specifically said "unaudited", not "hardened" because as Greg
mentioned the kernel must trust drivers, its devices that may not be
trusted.
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On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan
[off-list ref] wrote:
quoted
On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:
quoted
quoted
Add a new variant of pci_iomap for mapping all PCI resources
of a devices as shared memory with a hypervisor in a confidential
guest.
Signed-off-by: Andi Kleen<redacted>
Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@linux.intel.com>
I'm a bit puzzled by this part. So why should the guest*not* map
pci memory as shared? And if the answer is never (as it seems to be)
then why not just make regular pci_iomap DTRT?
It is in the context of confidential guest (where VMM is un-trusted). So
we don't want to make all PCI resource as shared. It should be allowed
only for hardened drivers/devices.
That's confusing, isn't device authorization what keeps unaudited
drivers from loading against untrusted devices? I'm feeling like
Michael that this should be a detail that drivers need not care about
explicitly, in which case it does not need to be exported because the
detail can be buried in lower levels.
We originally made it default (similar to AMD), but it during code audit we found a lot of drivers who do ioremap early outside the probe function. Since it would be difficult to change them all we made it opt-in, which ensures that only drivers that have been enabled can talk with the host at all and can't be attacked. That made the problem of hardening all these drivers a lot more practical.
Currently we only really need virtio and MSI-X shared, so for changing two places in the tree you avoid a lot of headache elsewhere.
Note there is still a command line option to override if you want to allow and load other drivers.
-Andi
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From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-08-24 09:47:20
On Mon, Aug 23, 2021 at 07:14:18PM -0700, Andi Kleen wrote:
On 8/23/2021 6:04 PM, Dan Williams wrote:
quoted
On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan
[off-list ref] wrote:
quoted
On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:
quoted
quoted
Add a new variant of pci_iomap for mapping all PCI resources
of a devices as shared memory with a hypervisor in a confidential
guest.
Signed-off-by: Andi Kleen<redacted>
Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@linux.intel.com>
I'm a bit puzzled by this part. So why should the guest*not* map
pci memory as shared? And if the answer is never (as it seems to be)
then why not just make regular pci_iomap DTRT?
It is in the context of confidential guest (where VMM is un-trusted). So
we don't want to make all PCI resource as shared. It should be allowed
only for hardened drivers/devices.
That's confusing, isn't device authorization what keeps unaudited
drivers from loading against untrusted devices? I'm feeling like
Michael that this should be a detail that drivers need not care about
explicitly, in which case it does not need to be exported because the
detail can be buried in lower levels.
We originally made it default (similar to AMD), but it during code audit we
found a lot of drivers who do ioremap early outside the probe function.
Since it would be difficult to change them all we made it opt-in, which
ensures that only drivers that have been enabled can talk with the host at
all and can't be attacked. That made the problem of hardening all these
drivers a lot more practical.
Currently we only really need virtio and MSI-X shared, so for changing two
places in the tree you avoid a lot of headache elsewhere.
Note there is still a command line option to override if you want to allow
and load other drivers.
-Andi
I see. Hmm. It's a bit of a random thing to do it at the map time
though. E.g. DMA is all handled transparently behind the DMA API.
Hardening is much more than just replacing map with map_shared
and I suspect what you will end up with is basically
vendors replacing map with map shared to make things work
for their users and washing their hands.
I would say an explicit flag in the driver that says "hardened"
and refusing to init a non hardened one would be better.
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I see. Hmm. It's a bit of a random thing to do it at the map time
though. E.g. DMA is all handled transparently behind the DMA API.
Hardening is much more than just replacing map with map_shared
and I suspect what you will end up with is basically
vendors replacing map with map shared to make things work
for their users and washing their hands.
That concept exists too. There is a separate allow list for the drivers. So just adding shared to a driver is not enough, until it's also added to the allowlist
Users can of course chose to disable the allowlist, but they need to understand the security implications.
I would say an explicit flag in the driver that says "hardened"
and refusing to init a non hardened one would be better.
We have that too (that's the device filtering)
But the problem is that device filtering just stops the probe functions, not the initcalls, and lot of legacy drivers do MMIO interactions before going into probe. In some cases it's unavoidable because of the device doesn't have a separate enumeration mechanism it needs some kind of probing to even check for its existence And since we don't want to change all of them it's far safer to make the ioremap opt-in.
-Andi
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[+cc Rajat; I still don't know what "shared memory with a hypervisor
in a confidential guest" means, but now we're talking about hardened
drivers and allow lists, which Rajat is interested in]
On Tue, Aug 24, 2021 at 10:20:44AM -0700, Andi Kleen wrote:
quoted
I see. Hmm. It's a bit of a random thing to do it at the map time
though. E.g. DMA is all handled transparently behind the DMA API.
Hardening is much more than just replacing map with map_shared
and I suspect what you will end up with is basically
vendors replacing map with map shared to make things work
for their users and washing their hands.
That concept exists too. There is a separate allow list for the drivers. So
just adding shared to a driver is not enough, until it's also added to the
allowlist
Users can of course chose to disable the allowlist, but they need to
understand the security implications.
quoted
I would say an explicit flag in the driver that says "hardened"
and refusing to init a non hardened one would be better.
We have that too (that's the device filtering)
But the problem is that device filtering just stops the probe functions, not
the initcalls, and lot of legacy drivers do MMIO interactions before going
into probe. In some cases it's unavoidable because of the device doesn't
have a separate enumeration mechanism it needs some kind of probing to even
check for its existence And since we don't want to change all of them it's
far safer to make the ioremap opt-in.
-Andi
[+cc Rajat; I still don't know what "shared memory with a hypervisor
in a confidential guest" means,
A confidential guest is a guest which uses memory encryption to isolate itself from the host. It doesn't trust the host. But it still needs to communicate with the host for IO, so it has some special memory areas that are explicitly marked shared. These are used to do IO with the host. All their usage needs to be carefully hardened to avoid any security attacks on the guest, that's why we want to limit this interaction only to a small set of hardened drivers. For MMIO, the set is currently only virtio and MSI-X.
-Andi
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On Tue, Aug 24, 2021 at 01:14:02PM -0700, Andi Kleen wrote:
On 8/24/2021 11:55 AM, Bjorn Helgaas wrote:
quoted
[+cc Rajat; I still don't know what "shared memory with a hypervisor
in a confidential guest" means,
A confidential guest is a guest which uses memory encryption to isolate
itself from the host. It doesn't trust the host. But it still needs to
communicate with the host for IO, so it has some special memory areas that
are explicitly marked shared. These are used to do IO with the host. All
their usage needs to be carefully hardened to avoid any security attacks on
the guest, that's why we want to limit this interaction only to a small set
of hardened drivers. For MMIO, the set is currently only virtio and MSI-X.
On Tue, Aug 24, 2021 at 01:14:02PM -0700, Andi Kleen wrote:
quoted
On 8/24/2021 11:55 AM, Bjorn Helgaas wrote:
quoted
[+cc Rajat; I still don't know what "shared memory with a hypervisor
in a confidential guest" means,
A confidential guest is a guest which uses memory encryption to isolate
itself from the host. It doesn't trust the host. But it still needs to
communicate with the host for IO, so it has some special memory areas that
are explicitly marked shared. These are used to do IO with the host. All
their usage needs to be carefully hardened to avoid any security attacks on
the guest, that's why we want to limit this interaction only to a small set
of hardened drivers. For MMIO, the set is currently only virtio and MSI-X.
Good material for the commit log next time around. Thanks!
This is all in the patch intro too, which should make it into the merge commits.
I don't think we can reexplain the basic concepts for every individual patch in a large patch kit.
-Andi
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From: Dan Williams <hidden> Date: 2021-08-24 21:05:42
On Tue, Aug 24, 2021 at 1:50 PM Andi Kleen [off-list ref] wrote:
On 8/24/2021 1:31 PM, Bjorn Helgaas wrote:
quoted
On Tue, Aug 24, 2021 at 01:14:02PM -0700, Andi Kleen wrote:
quoted
On 8/24/2021 11:55 AM, Bjorn Helgaas wrote:
quoted
[+cc Rajat; I still don't know what "shared memory with a hypervisor
in a confidential guest" means,
A confidential guest is a guest which uses memory encryption to isolate
itself from the host. It doesn't trust the host. But it still needs to
communicate with the host for IO, so it has some special memory areas that
are explicitly marked shared. These are used to do IO with the host. All
their usage needs to be carefully hardened to avoid any security attacks on
the guest, that's why we want to limit this interaction only to a small set
of hardened drivers. For MMIO, the set is currently only virtio and MSI-X.
Good material for the commit log next time around. Thanks!
This is all in the patch intro too, which should make it into the merge
commits.
I don't think we can reexplain the basic concepts for every individual
patch in a large patch kit.
Maybe not the whole cover letter, but how about just a line in this
one that says "Recall that 'shared' in this context refers to memory
that lacks confidentiality and integrity protection from the VMM so
that it can communicate with the VM." Although I think
ioremap_noprotect() might be clearer than shared for the protected
guest use case?
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On Tue, Aug 24, 2021 at 01:50:00PM -0700, Andi Kleen wrote:
On 8/24/2021 1:31 PM, Bjorn Helgaas wrote:
quoted
On Tue, Aug 24, 2021 at 01:14:02PM -0700, Andi Kleen wrote:
quoted
On 8/24/2021 11:55 AM, Bjorn Helgaas wrote:
quoted
[+cc Rajat; I still don't know what "shared memory with a hypervisor
in a confidential guest" means,
A confidential guest is a guest which uses memory encryption to isolate
itself from the host. It doesn't trust the host. But it still needs to
communicate with the host for IO, so it has some special memory areas that
are explicitly marked shared. These are used to do IO with the host. All
their usage needs to be carefully hardened to avoid any security attacks on
the guest, that's why we want to limit this interaction only to a small set
of hardened drivers. For MMIO, the set is currently only virtio and MSI-X.
Good material for the commit log next time around. Thanks!
This is all in the patch intro too, which should make it into the merge
commits.
It's good if the cover letter makes into the merge commit log.
It's probably just because my git foo is lacking, but merge commit
logs don't seem as discoverable as the actual patch commit logs. Five
years from now, if I want to learn about pci_iomap_shared() history, I
would "git log -p lib/pci_iomap.c" and search for it. But I don't
think I would see the merge commit then.
Bjorn
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From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-08-29 15:27:56
On Tue, Aug 24, 2021 at 10:20:44AM -0700, Andi Kleen wrote:
quoted
I see. Hmm. It's a bit of a random thing to do it at the map time
though. E.g. DMA is all handled transparently behind the DMA API.
Hardening is much more than just replacing map with map_shared
and I suspect what you will end up with is basically
vendors replacing map with map shared to make things work
for their users and washing their hands.
That concept exists too. There is a separate allow list for the drivers. So
just adding shared to a driver is not enough, until it's also added to the
allowlist
Users can of course chose to disable the allowlist, but they need to
understand the security implications.
Right. So given that, why do we need to tweak a random API like the map?
If you just make all maps be shared then the user is in control.
Seems sensible to me.
quoted
I would say an explicit flag in the driver that says "hardened"
and refusing to init a non hardened one would be better.
We have that too (that's the device filtering)
But the problem is that device filtering just stops the probe functions, not
the initcalls, and lot of legacy drivers do MMIO interactions before going
into probe. In some cases it's unavoidable because of the device doesn't
have a separate enumeration mechanism it needs some kind of probing to even
check for its existence And since we don't want to change all of them it's
far safer to make the ioremap opt-in.
-Andi
Let's be frank, even without encryption disabling most drivers -
especially weird ones that poke at hardware before probe -
is far safer than keeping them, but one loses a bunch of features.
IOW all this hardening is nice but which security/feature tradeoff
to take it a policy decision, not something kernel should do
imho.
--
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Let's be frank, even without encryption disabling most drivers -
especially weird ones that poke at hardware before probe -
is far safer than keeping them, but one loses a bunch of features.
Usually we don't lose features at all. None of the legacy drivers are needed on a guest (or even a modern native system). It's all just all for old hardware. Maybe in 20+ years it can be all removed, but we can't wait that long.
IOW all this hardening is nice but which security/feature tradeoff
to take it a policy decision, not something kernel should do
imho.
There's no mechanism to push this kind of policy to user space. Users don't have control what initcalls run. At the time they execute there isn't even any user space yet.
Even if they could somehow control them it's very unlikely they would understand them and make an informed decision.
Doing it at build time is not feasible either since we want to run on standard distribution kernels.
For modules we have a policy mechanism (prevent udev probing by preventing enumeration), and that is implemented, but only handling modules is not enough. The compiled in drivers have to be handled too, otherwise you have gaping holes in the protection. We don't prevent users manually loading modules that might probe, but that is a policy decision that users actually sensibly make in user space.
Also I changing this single call really that bad? It's not that we changing anything drastic here, just give the low level subsystem a better hint about the intention. If you don't like the function name, could make it an argument instead?
-Andi
From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-08-29 22:26:34
On Sun, Aug 29, 2021 at 09:17:53AM -0700, Andi Kleen wrote:
Also I changing this single call really that bad? It's not that we changing
anything drastic here, just give the low level subsystem a better hint about
the intention. If you don't like the function name, could make it an
argument instead?
My point however is that the API should say that the
driver has been audited, not that the mapping has been
done in some special way. For example the mapping can be
in some kind of wrapper, not directly in the driver.
However you want the driver validated, not the wrapper.
Here's an idea:
Now any audited driver must do
#include <linux/audited.h>
first of all.
Implementation-wise it can do any number of things,
e.g. if you like then sure you can do:
#ifdef AUDITED_MODULE
#define pci_ioremap pci_ioremap_shared
#else
#define pci_ioremap pci_ioremap
#endif
but you can also thinkably do something like (won't work,
but just to give you the idea):
#ifdef AUDITED_MODULE
#define __init __init
#else
#define __init
#endif
or any number of hacks like this.
--
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On Sun, Aug 29, 2021 at 09:17:53AM -0700, Andi Kleen wrote:
quoted
Also I changing this single call really that bad? It's not that we changing
anything drastic here, just give the low level subsystem a better hint about
the intention. If you don't like the function name, could make it an
argument instead?
My point however is that the API should say that the
driver has been audited,
We have that status in the struct device. If you want to tie the ioremap to that we could define a ioremap_device() with a device argument and decide based on that.
Or we can add _audited to the name. ioremap_shared_audited?
not that the mapping has been
done in some special way. For example the mapping can be
in some kind of wrapper, not directly in the driver.
However you want the driver validated, not the wrapper.
Here's an idea:
I don't think magic differences of API behavior based on some define are a good idea. That's easy to miss.
That's a "COME FROM" in API design.
Also it wouldn't handle the case that a driver has both private and shared ioremaps, e.g. for BIOS structures.
And we've been avoiding that drivers can self declare auditing, we've been trying to have a separate centralized list so that it's easier to enforce and avoids any cut'n'paste mistakes.
-Andi
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From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-08-30 21:00:05
On Sun, Aug 29, 2021 at 10:11:46PM -0700, Andi Kleen wrote:
On 8/29/2021 3:26 PM, Michael S. Tsirkin wrote:
quoted
On Sun, Aug 29, 2021 at 09:17:53AM -0700, Andi Kleen wrote:
quoted
Also I changing this single call really that bad? It's not that we changing
anything drastic here, just give the low level subsystem a better hint about
the intention. If you don't like the function name, could make it an
argument instead?
My point however is that the API should say that the
driver has been audited,
We have that status in the struct device. If you want to tie the ioremap to
that we could define a ioremap_device() with a device argument and decide
based on that.
But it's not the device that is audited. And it's not the device
that might be secure or insecure. It's the driver.
Or we can add _audited to the name. ioremap_shared_audited?
But it's not the mapping that has to be done in handled special way.
It's any data we get from device, not all of it coming from IO, e.g.
there's DMA and interrupts that all have to be validated.
Wouldn't you say that what is really wanted is just not running
unaudited drivers in the first place?
quoted
not that the mapping has been
done in some special way. For example the mapping can be
in some kind of wrapper, not directly in the driver.
However you want the driver validated, not the wrapper.
Here's an idea:
I don't think magic differences of API behavior based on some define are a
good idea. That's easy to miss.
Well ... my point is that actually there is no difference in API
behaviour. the map is the same map, exactly same data goes to device. If
anything any non-shared map is special in that encrypted data goes to
device.
That's a "COME FROM" in API design.
Also it wouldn't handle the case that a driver has both private and shared
ioremaps, e.g. for BIOS structures.
Hmm. Interesting. It's bios maps that are unusual and need to be private though ...
And we've been avoiding that drivers can self declare auditing, we've been
trying to have a separate centralized list so that it's easier to enforce
and avoids any cut'n'paste mistakes.
-Andi
Now I'm confused. What is proposed here seems to be basically that,
drivers need to declare auditing by replacing ioremap with
ioremap_shared.
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Or we can add _audited to the name. ioremap_shared_audited?
But it's not the mapping that has to be done in handled special way.
It's any data we get from device, not all of it coming from IO, e.g.
there's DMA and interrupts that all have to be validated.
Wouldn't you say that what is really wanted is just not running
unaudited drivers in the first place?
Yes.
quoted
And we've been avoiding that drivers can self declare auditing, we've been
trying to have a separate centralized list so that it's easier to enforce
and avoids any cut'n'paste mistakes.
-Andi
Now I'm confused. What is proposed here seems to be basically that,
drivers need to declare auditing by replacing ioremap with
ioremap_shared.
Auditing is declared on the device model level using a central allow list.
But this cannot do anything to initcalls that run before probe, that's why an extra level of defense of ioremap opt-in is useful. But it's not the primary mechanism to declare a driver audited, that's the allow list. The ioremap is just another mechanism to avoid having to touch a lot of legacy drivers.
If we agree on that then the original proposed semantics of "ioremap_shared" may be acceptable?
-Andi
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From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-09-10 09:54:43
On Mon, Aug 30, 2021 at 05:23:17PM -0700, Andi Kleen wrote:
On 8/30/2021 1:59 PM, Michael S. Tsirkin wrote:
quoted
quoted
Or we can add _audited to the name. ioremap_shared_audited?
But it's not the mapping that has to be done in handled special way.
It's any data we get from device, not all of it coming from IO, e.g.
there's DMA and interrupts that all have to be validated.
Wouldn't you say that what is really wanted is just not running
unaudited drivers in the first place?
Yes.
Then ... let's do just that?
quoted
quoted
And we've been avoiding that drivers can self declare auditing, we've been
trying to have a separate centralized list so that it's easier to enforce
and avoids any cut'n'paste mistakes.
-Andi
Now I'm confused. What is proposed here seems to be basically that,
drivers need to declare auditing by replacing ioremap with
ioremap_shared.
Auditing is declared on the device model level using a central allow list.
Can we not have an init call allow list instead of, or in addition to, a
device allow list?
But this cannot do anything to initcalls that run before probe,
Can't we extend module_init so init calls are validated against the
allow list?
that's why
an extra level of defense of ioremap opt-in is useful.
OK even assuming this, why is pci_iomap opt-in useful?
That never happens before probe - there's simply no pci_device then.
But it's not the
primary mechanism to declare a driver audited, that's the allow list. The
ioremap is just another mechanism to avoid having to touch a lot of legacy
drivers.
If we agree on that then the original proposed semantics of "ioremap_shared"
may be acceptable?
-Andi
It looks suspiciously like drivers self-declaring auditing to me which
we both seem to agree is undesirable. What exactly is the difference?
Or are you just trying to disable anything that runs before probe?
In that case I don't see a reason to touch pci drivers though.
These should be fine with just the device model list.
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And we've been avoiding that drivers can self declare auditing, we've been
trying to have a separate centralized list so that it's easier to enforce
and avoids any cut'n'paste mistakes.
-Andi
Now I'm confused. What is proposed here seems to be basically that,
drivers need to declare auditing by replacing ioremap with
ioremap_shared.
Auditing is declared on the device model level using a central allow list.
Can we not have an init call allow list instead of, or in addition to, a
device allow list?
That would be quite complicated and intrusive. In fact I'm not even sure how to do maintain something like this. There are a lot of needed initcalls, they would all need to be marked. How can we distinguish them? It would be a giant auditing project. And of course how would you prevent it from bitrotting?
Basically it would be hundreds of changes all over the tree, just to avoid two changes in virtio and MSI. Approach of just stopping the initcalls from doing bad things is much less intrusive.
quoted
But this cannot do anything to initcalls that run before probe,
Can't we extend module_init so init calls are validated against the
allow list?
See above.
Also the problem isn't really with modules (we rely on udev not loading them), but with builtin initcalls
quoted
that's why
an extra level of defense of ioremap opt-in is useful.
OK even assuming this, why is pci_iomap opt-in useful?
That never happens before probe - there's simply no pci_device then.
Hmm, yes that's true. I guess we can make it default to opt-in for pci_iomap.
It only really matters for device less ioremaps.
It looks suspiciously like drivers self-declaring auditing to me which
we both seem to agree is undesirable. What exactly is the difference?
Just allow listing the ioremaps is not self declaration because the device will still not initialize due to the central device filter. If you want to use it that has to be changed.
It's just an additional safety net to contain code running before probe.
Or are you just trying to disable anything that runs before probe?
Well anything that could do dangerous host interactions (like processing ioremap data) A lot of things are harmless and can be allowed, or already blocked elsewhere (e.g. we have a IO port filter). This just handles the ioremap/MMIO case.
In that case I don't see a reason to touch pci drivers though.
These should be fine with just the device model list.
From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-09-11 23:54:50
On Fri, Sep 10, 2021 at 09:34:45AM -0700, Andi Kleen wrote:
quoted
quoted
that's why
an extra level of defense of ioremap opt-in is useful.
OK even assuming this, why is pci_iomap opt-in useful?
That never happens before probe - there's simply no pci_device then.
Hmm, yes that's true. I guess we can make it default to opt-in for
pci_iomap.
It only really matters for device less ioremaps.
OK. And same thing for other things with device, such as
devm_platform_ioremap_resource.
If we agree on all that, this will basically remove virtio
changes from the picture ;)
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From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-09-13 05:53:42
On Sat, Sep 11, 2021 at 07:54:43PM -0400, Michael S. Tsirkin wrote:
On Fri, Sep 10, 2021 at 09:34:45AM -0700, Andi Kleen wrote:
quoted
quoted
quoted
that's why
an extra level of defense of ioremap opt-in is useful.
OK even assuming this, why is pci_iomap opt-in useful?
That never happens before probe - there's simply no pci_device then.
Hmm, yes that's true. I guess we can make it default to opt-in for
pci_iomap.
It only really matters for device less ioremaps.
OK. And same thing for other things with device, such as
devm_platform_ioremap_resource.
If we agree on all that, this will basically remove virtio
changes from the picture ;)
Something else that was pointed out to me:
fs->window_kaddr = devm_memremap_pages(&vdev->dev, pgmap);
if (IS_ERR(fs->window_kaddr))
return PTR_ERR(fs->window_kaddr);
looks like if we forget to set the shared flag then it will
corrupt the DAX data?
Hmm, yes that's true. I guess we can make it default to opt-in for
pci_iomap.
It only really matters for device less ioremaps.
OK. And same thing for other things with device, such as
devm_platform_ioremap_resource.
If we agree on all that, this will basically remove virtio
changes from the picture ;)
Hi we revisited this now. One problem with removing the ioremap opt-in is that it's still possible for drivers to get at devices without going through probe. For example they can walk the PCI device list. Some drivers do that for various reasons. So if we remove the opt-in we would need to audit and possibly fix all that, which would be potentially a lot of churn. That's why I think it's better to keep the opt-in.
-Andi
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From: "Michael S. Tsirkin" <mst@redhat.com> Date: 2021-09-27 09:07:58
On Fri, Sep 24, 2021 at 03:43:40PM -0700, Andi Kleen wrote:
quoted
quoted
Hmm, yes that's true. I guess we can make it default to opt-in for
pci_iomap.
It only really matters for device less ioremaps.
OK. And same thing for other things with device, such as
devm_platform_ioremap_resource.
If we agree on all that, this will basically remove virtio
changes from the picture ;)
Hi we revisited this now. One problem with removing the ioremap opt-in is
that it's still possible for drivers to get at devices without going through
probe. For example they can walk the PCI device list. Some drivers do that
for various reasons. So if we remove the opt-in we would need to audit and
possibly fix all that, which would be potentially a lot of churn. That's why
I think it's better to keep the opt-in.
-Andi
I've been thinking about why this still feels wrong to me.
Here's what I came up with: at some point someone will want one of these
modules (poking at devices in the initcall) in the encrypted
environment, and will change ioremap to ioremap_shared.
At that point the allowlist will be broken again, and
by that time it will be set in stone and too late to fix.
Isn't the problem that what is actually audited is modules,
but you are trying to add devices to allow list?
So why not have modules/initcalls in the allowlist then?
For built-in modules, we already have initcall_blacklisted, right?
This could be an extension ... no?
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