[PATCH 11/40] nitro_enclaves: Add NE_ENCLAVE_PCIE_MODE launch flag

[Alexander Graf <graf@amazon.com>]

Nitro Sandboxes give their guest virtio devices that the parent
provides, on a PCIe bus. The hypervisor sets up that bus when it
allocates the slot, so user space asks for it with a launch flag.

Define NE_ENCLAVE_PCIE_MODE, the first launch flag, and forward it in
SLOT_ALLOC. struct slot_alloc_req gains a flag word, and at offset 0,
over the unused field, a payload_version byte that tells the device to
read it. We send version 1 when a flag is set, and the all-zero request
of today otherwise.

A device that takes launch flags publishes a vendor-specific PCI
capability. A device that predates them ignores the flag word and
allocates a plain slot, so refuse a launch flag with -EOPNOTSUPP on a
device without the capability.

Signed-off-by: Alexander Graf <graf@amazon.com>
---
 drivers/virt/nitro_enclaves/ne_misc_dev.c | 19 ++++++++++++++++++-
 drivers/virt/nitro_enclaves/ne_pci_dev.h  | 23 +++++++++++++++++++++--
 include/uapi/linux/nitro_enclaves.h       | 14 ++++++++++++++
 3 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/drivers/virt/nitro_enclaves/ne_misc_dev.c b/drivers/virt/nitro_enclaves/ne_misc_dev.c
index 68c497df4f14b..0bf62f703806e 100644
--- a/drivers/virt/nitro_enclaves/ne_misc_dev.c
+++ b/drivers/virt/nitro_enclaves/ne_misc_dev.c
@@ -2475,13 +2475,30 @@ static int ne_create_vm_ioctl(struct ne_pci_dev *ne_pci_dev, u64 flags,
 	int rc = -EINVAL;
 	struct slot_alloc_req slot_alloc_req = {};
 
-	if (flags) {
+	if (flags & ~(u64)NE_ENCLAVE_PCIE_MODE) {
 		dev_err_ratelimited(ne_misc_dev.this_device,
 				    "Unknown launch flag bit set 0x%llx\n", flags);
 
 		return -NE_ERR_INVALID_FLAG_VALUE;
 	}
 
+	/*
+	 * A device that takes launch flags publishes a vendor-specific
+	 * capability. One without it takes no launch flags and would allocate a
+	 * slot without the properties they ask for.
+	 */
+	if (flags && !pci_find_capability(ne_pci_dev->pdev, PCI_CAP_ID_VNDR)) {
+		dev_err_ratelimited(ne_misc_dev.this_device,
+				    "Device takes no launch flags\n");
+
+		return -EOPNOTSUPP;
+	}
+
+	if (flags) {
+		slot_alloc_req.payload_version = 1;
+		slot_alloc_req.flags = flags;
+	}
+
 	mutex_lock(&ne_cpu_pool.mutex);
 
 	for (i = 0; i < ne_cpu_pool.nr_parent_vm_cores; i++)
diff --git a/drivers/virt/nitro_enclaves/ne_pci_dev.h b/drivers/virt/nitro_enclaves/ne_pci_dev.h
index 19e129d14a3a0..b0957e2606ec3 100644
--- a/drivers/virt/nitro_enclaves/ne_pci_dev.h
+++ b/drivers/virt/nitro_enclaves/ne_pci_dev.h
@@ -7,10 +7,12 @@
 #define _NE_PCI_DEV_H_
 
 #include <linux/atomic.h>
+#include <linux/build_bug.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
 #include <linux/pci.h>
 #include <linux/pci_ids.h>
+#include <linux/stddef.h>
 #include <linux/wait.h>
 
 /**
@@ -174,12 +176,29 @@ struct enclave_stop_req {
 
 /**
  * struct slot_alloc_req - SLOT_ALLOC request.
- * @unused:	In order to avoid weird sizeof edge cases.
+ * @payload_version:	Wire version at offset 0. Zero is the value a driver
+ *			without launch flags leaves here, and tells the device
+ *			to disregard @reserved and @flags. 1 means @flags is
+ *			valid.
+ * @reserved:		Alignment padding between @payload_version and
+ *			@flags. Zero.
+ * @flags:		Launch flag word from NE_CREATE_VM2, valid when
+ *			@payload_version >= 1.
  */
 struct slot_alloc_req {
-	u8	unused;
+	u8	payload_version;
+	u8	reserved[3];
+	u32	flags;
 };
 
+/*
+ * The device picks these fields out of the payload by offset, so a change
+ * to the layout here changes the SLOT_ALLOC wire format.
+ */
+static_assert(sizeof(struct slot_alloc_req) == 8);
+static_assert(offsetof(struct slot_alloc_req, reserved) == 1);
+static_assert(offsetof(struct slot_alloc_req, flags) == 4);
+
 /**
  * struct slot_free_req - SLOT_FREE request.
  * @slot_uid:	Slot unique id mapped to the slot to free.
diff --git a/include/uapi/linux/nitro_enclaves.h b/include/uapi/linux/nitro_enclaves.h
index 8e43be9a0a1fa..8ccf16e9cf5fb 100644
--- a/include/uapi/linux/nitro_enclaves.h
+++ b/include/uapi/linux/nitro_enclaves.h
@@ -46,6 +46,18 @@
  */
 #define NE_CREATE_VM			_IOR(0xAE, 0x20, __u64)
 
+/**
+ * DOC: NE_CREATE_VM2 launch flags
+ */
+
+/**
+ * NE_ENCLAVE_PCIE_MODE - Allocate a slot with a PCIe bus. The
+ *			  hypervisor selects PCIe backing for the slot at
+ *			  SLOT_ALLOC time, so a caller that wants it asks
+ *			  for it here and not at enclave start.
+ */
+#define NE_ENCLAVE_PCIE_MODE		(1u << 6)
+
 /**
  * struct ne_create_vm_args - NE_CREATE_VM2 argument (in / out).
  * @flags:	Launch-time flag word (in). Flags select properties of the
@@ -82,6 +94,8 @@ struct ne_create_vm_args {
  * * EFAULT				- Argument read or write failure.
  * * NE_ERR_INVALID_FLAG_VALUE		- Unknown flag bit set, or
  *					  NE_ENCLAVE_DEBUG_MODE set.
+ * * EOPNOTSUPP			- A launch flag is set and the NE PCI
+ *					  device takes no launch flags.
  * * EINVAL				- The argument stops before @slot_uid.
  * * E2BIG				- The argument carries a field this kernel
  *					  does not know, set to a non-zero value.
-- 
2.47.1