x86/sgx: Add an SGX misc driver interface

Intel(R) SGX is a new hardware functionality that can be used by
applications to set aside private regions of code and data called
enclaves. New hardware protects enclave code and data from outside
access and modification.

Add a driver that presents a device file and ioctl API to build and
manage enclaves.

 [ bp: Small touchups, remove unused encl variable in sgx_encl_find() as
   Reported-by: kernel test robot <lkp@intel.com> ]

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Jethro Beekman <jethro@fortanix.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-12-jarkko@kernel.org

1 files changed, 146 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
new file mode 100644
index 000000000000..b9d445db7ff1
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+/*  Copyright(c) 2016-20 Intel Corporation. */
+
+#include <linux/lockdep.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/shmem_fs.h>
+#include <linux/suspend.h>
+#include <linux/sched/mm.h>
+#include "arch.h"
+#include "encl.h"
+#include "encls.h"
+#include "sgx.h"
+
+static struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
+						unsigned long addr,
+						unsigned long vm_flags)
+{
+	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
+	struct sgx_encl_page *entry;
+
+	entry = xa_load(&encl->page_array, PFN_DOWN(addr));
+	if (!entry)
+		return ERR_PTR(-EFAULT);
+
+	/*
+	 * Verify that the faulted page has equal or higher build time
+	 * permissions than the VMA permissions (i.e. the subset of {VM_READ,
+	 * VM_WRITE, VM_EXECUTE} in vma->vm_flags).
+	 */
+	if ((entry->vm_max_prot_bits & vm_prot_bits) != vm_prot_bits)
+		return ERR_PTR(-EFAULT);
+
+	/* No page found. */
+	if (!entry->epc_page)
+		return ERR_PTR(-EFAULT);
+
+	/* Entry successfully located. */
+	return entry;
+}
+
+static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
+{
+	unsigned long addr = (unsigned long)vmf->address;
+	struct vm_area_struct *vma = vmf->vma;
+	struct sgx_encl_page *entry;
+	unsigned long phys_addr;
+	struct sgx_encl *encl;
+	vm_fault_t ret;
+
+	encl = vma->vm_private_data;
+
+	mutex_lock(&encl->lock);
+
+	entry = sgx_encl_load_page(encl, addr, vma->vm_flags);
+	if (IS_ERR(entry)) {
+		mutex_unlock(&encl->lock);
+
+		return VM_FAULT_SIGBUS;
+	}
+
+	phys_addr = sgx_get_epc_phys_addr(entry->epc_page);
+
+	ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr));
+	if (ret != VM_FAULT_NOPAGE) {
+		mutex_unlock(&encl->lock);
+
+		return VM_FAULT_SIGBUS;
+	}
+
+	mutex_unlock(&encl->lock);
+
+	return VM_FAULT_NOPAGE;
+}
+
+/**
+ * sgx_encl_may_map() - Check if a requested VMA mapping is allowed
+ * @encl:		an enclave pointer
+ * @start:		lower bound of the address range, inclusive
+ * @end:		upper bound of the address range, exclusive
+ * @vm_flags:		VMA flags
+ *
+ * Iterate through the enclave pages contained within [@start, @end) to verify
+ * that the permissions requested by a subset of {VM_READ, VM_WRITE, VM_EXEC}
+ * do not contain any permissions that are not contained in the build time
+ * permissions of any of the enclave pages within the given address range.
+ *
+ * An enclave creator must declare the strongest permissions that will be
+ * needed for each enclave page. This ensures that mappings have the identical
+ * or weaker permissions than the earlier declared permissions.
+ *
+ * Return: 0 on success, -EACCES otherwise
+ */
+int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
+		     unsigned long end, unsigned long vm_flags)
+{
+	unsigned long vm_prot_bits = vm_flags & (VM_READ | VM_WRITE | VM_EXEC);
+	struct sgx_encl_page *page;
+	unsigned long count = 0;
+	int ret = 0;
+
+	XA_STATE(xas, &encl->page_array, PFN_DOWN(start));
+
+	/*
+	 * Disallow READ_IMPLIES_EXEC tasks as their VMA permissions might
+	 * conflict with the enclave page permissions.
+	 */
+	if (current->personality & READ_IMPLIES_EXEC)
+		return -EACCES;
+
+	mutex_lock(&encl->lock);
+	xas_lock(&xas);
+	xas_for_each(&xas, page, PFN_DOWN(end - 1)) {
+		if (~page->vm_max_prot_bits & vm_prot_bits) {
+			ret = -EACCES;
+			break;
+		}
+
+		/* Reschedule on every XA_CHECK_SCHED iteration. */
+		if (!(++count % XA_CHECK_SCHED)) {
+			xas_pause(&xas);
+			xas_unlock(&xas);
+			mutex_unlock(&encl->lock);
+
+			cond_resched();
+
+			mutex_lock(&encl->lock);
+			xas_lock(&xas);
+		}
+	}
+	xas_unlock(&xas);
+	mutex_unlock(&encl->lock);
+
+	return ret;
+}
+
+static int sgx_vma_mprotect(struct vm_area_struct *vma, unsigned long start,
+			    unsigned long end, unsigned long newflags)
+{
+	return sgx_encl_may_map(vma->vm_private_data, start, end, newflags);
+}
+
+const struct vm_operations_struct sgx_vm_ops = {
+	.fault = sgx_vma_fault,
+	.mprotect = sgx_vma_mprotect,
+};