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Re: [Xen-devel] [PATCH v3 4/6] xen/arm: zynqmp: eemi access control


Sorry I forgot to answer to the rest of the e-mail.

On 10/16/2018 03:39 AM, Stefano Stabellini wrote:
On 15/10/2018 08:25, Julien Grall wrote:
+    bool hwdom_access;    /* HW domain gets access regardless.  */
+ * This table maps a node into a memory address.
+ * If a guest has access to the address, it has enough control
+ * over the node to grant it access to EEMI calls for that node.
+ */
+static const struct pm_access pm_node_access[] = {


+ * This table maps reset line IDs into a memory address.
+ * If a guest has access to the address, it has enough control
+ * over the affected node to grant it access to EEMI calls for
+ * resetting that node.
+ */
+static const struct pm_access pm_reset_access[] = {


+ * This table maps reset line IDs into a memory address.
+ * If a guest has access to the address, it has enough control
+ * over the affected node to grant it access to EEMI calls for
+ * resetting that node.
+ */
+static const struct {
+    paddr_t start;
+    paddr_t size;
+    uint32_t mask;   /* Zero means no mask, i.e all bits.  */
+    enum pm_node_id node;
+    bool hwdom_access;
+    bool readonly;
+} pm_mmio_access[] = {

Those 3 arrays contains a lot of hardcoded value. Can't any of this be
detected from the device-tree?

No, the information is not available on device tree unfortunately. >

I would be interested to know how this is going to work with upstream
Do you hardcode all the values there as well?

Yes: the IDs are specified on an header file, see
include/linux/firmware/xlnx-zynqmp.h on the zynq/firmware branch of the
arm-soc tree. In addition to the IDs, we also have the memory addresses
in Xen to do the permission checks.

I am afraid this is not linux upstream. Can you point to the code in Linus's
git or explain the state of the review?

It hasn't been pulled into Linux yet, I was told it has already been
reviewed and is queued in arm-soc for upstreaming at the next merge
window, which should be imminent.

Looking at that branch, I can see some DT bindings at least for the clock. I also don't see any hardcoded value for device so far in that series. Is it going to be sent separately?

+static bool pm_check_access(const struct pm_access *acl, struct
domain *d,
+                            uint32_t idx)
+    unsigned long mfn;

mfn_t please. The code is not that nice but at least it add more safety
in the
code. Hopefully iommu_access_permitted will be converted to typesafe MFN

Yes, I can make this change without issues.

+    if ( acl[idx].hwdom_access && is_hardware_domain(d) )
+        return true;
+    if ( !acl[idx].addr )
+        return false;
+    mfn = PFN_DOWN(acl[idx].addr);



+    return iomem_access_permitted(d, mfn, mfn);

Is the address something that a guest would be allowed to read/write
If not, then iomem_access_permitted(...) should not be used.

Yes, the address would be something remapped to the guest using iomem.

In the documentation at the beginning of the file you say that memory ranges
are typically secure memory. So how a guest can access them directly?

I probably need a bit more background here... What is the address correspond
to at the end?

The address corresponds to the MMIO region of the device. For instance,
MM_GEM0 is 0xff0b0000, which is the address of the network card. It is
accessible. The same goes for MM_CAN0, MM_TTC0, MM_SD0, and all the
others -- they are all accessible. These are the addresses used in this
check that should be remapped into the guest.

However, things are different for the pm_mmio_access array used in
domain_has_mmio_access to check for access rights. (That is also where
the mask is applied to writes and not to reads, see below.) In that
case, the addresses correspond to single registers inside the
zynqmp-psgtr region ("ZynqMP High Speed Processing System Gigabit
Transceiver") and pin controller region. As you can see, in
domain_has_mmio_access the access checks are still done on the
corresponding node address, which is the one that gets remapped. For
instance in the case of the network card, the remapped address is
0xff0b0000, checks are done on it, but the zynqmp-psgtr and pin
contoller region registers are:

     .start = MM_CRL_APB + R_CRL_GEM0_REF_CTRL,
     .size = 4, .node = NODE_ETH_0
     .start = MM_IOU_SLCR + R_IOU_SLCR_IOU_RAM_GEM0,
     .size = 4, .node = NODE_ETH_0

The comment comes from Edgar, but I think that he meant that VMs won't
be able to write to these regions directly. I'll improve the comment.

Thank you for the explanation. Can you add something similar to what you wrote in the code?


Julien Grall

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