[PATCH 4/6] intel_sgx: ptrace() support for the driver

[Jarkko Sakkinen]

This commit implements the 'access' callback for the enclave VMA thus
enabling reading and writing the memory of debug enclaves. The page
that is accessed is first faulted and marked as reserved so that the
EPC evictor will know not to swap the page while it is being
manipulated.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
---
 drivers/staging/intel_sgx/isgx_vma.c | 118 +++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)

diff --git a/drivers/staging/intel_sgx/isgx_vma.c b/drivers/staging/intel_sgx/isgx_vma.c
index f6cfb02..2788ab9 100644
--- a/drivers/staging/intel_sgx/isgx_vma.c
+++ b/drivers/staging/intel_sgx/isgx_vma.c
@@ -275,8 +275,126 @@ static int isgx_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 }
 
+static inline int isgx_vma_access_word(struct isgx_enclave *enclave,
+				       unsigned long addr,
+				       void *buf,
+				       int len,
+				       int write,
+				       struct isgx_enclave_page *enclave_page,
+				       int i)
+{
+	char data[sizeof(unsigned long)];
+	int align, cnt, offset;
+	void *vaddr;
+	int ret;
+
+	offset = ((addr + i) & (PAGE_SIZE - 1)) & ~(sizeof(unsigned long) - 1);
+	align = (addr + i) & (sizeof(unsigned long) - 1);
+	cnt = sizeof(unsigned long) - align;
+	cnt = min(cnt, len - i);
+
+	if (write) {
+		if (enclave_page->flags & ISGX_ENCLAVE_PAGE_TCS &&
+		    (offset < 8 || (offset + (len - i)) > 16))
+			return -ECANCELED;
+
+		if (align || (cnt != sizeof(unsigned long))) {
+			vaddr = isgx_get_epc_page(enclave_page->epc_page);
+			ret = __edbgrd((void *)((unsigned long)vaddr + offset),
+				       (unsigned long *)data);
+			isgx_put_epc_page(vaddr);
+			if (ret) {
+				isgx_dbg(enclave, "EDBGRD returned %d\n", ret);
+				return -EFAULT;
+			}
+		}
+
+		memcpy(data + align, buf + i, cnt);
+		vaddr = isgx_get_epc_page(enclave_page->epc_page);
+		ret = __edbgwr((void *)((unsigned long)vaddr + offset),
+			       (unsigned long *)data);
+		isgx_put_epc_page(vaddr);
+		if (ret) {
+			isgx_dbg(enclave, "EDBGWR returned %d\n", ret);
+			return -EFAULT;
+		}
+	} else {
+		if (enclave_page->flags & ISGX_ENCLAVE_PAGE_TCS &&
+		    (offset + (len - i)) > 72)
+			return -ECANCELED;
+
+		vaddr = isgx_get_epc_page(enclave_page->epc_page);
+		ret = __edbgrd((void *)((unsigned long)vaddr + offset),
+			       (unsigned long *)data);
+		isgx_put_epc_page(vaddr);
+		if (ret) {
+			isgx_dbg(enclave, "EDBGRD returned %d\n", ret);
+			return -EFAULT;
+		}
+
+		memcpy(buf + i, data + align, cnt);
+	}
+
+	return cnt;
+}
+
+static int isgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
+			   void *buf, int len, int write)
+{
+	struct isgx_enclave *enclave = vma->vm_private_data;
+	struct isgx_enclave_page *entry = NULL;
+	const char *op_str = write ? "EDBGWR" : "EDBGRD";
+	int ret = 0;
+	int i;
+
+	/* If process was forked, VMA is still there but vm_private_data is set
+	 * to NULL.
+	 */
+	if (!enclave)
+		return -EFAULT;
+
+	if (!(enclave->flags & ISGX_ENCLAVE_DEBUG) ||
+	    !(enclave->flags & ISGX_ENCLAVE_INITIALIZED) ||
+	    (enclave->flags & ISGX_ENCLAVE_SUSPEND))
+		return -EFAULT;
+
+	isgx_dbg(enclave, "%s addr=0x%lx, len=%d\n", op_str, addr, len);
+
+	for (i = 0; i < len; i += ret) {
+		if (!entry || !((addr + i) & (PAGE_SIZE - 1))) {
+			if (entry)
+				entry->flags &= ~ISGX_ENCLAVE_PAGE_RESERVED;
+
+			do {
+				entry = isgx_vma_do_fault(
+					vma, (addr + i) & PAGE_MASK, true);
+			} while (entry == ERR_PTR(-EBUSY));
+
+			if (IS_ERR(entry)) {
+				ret = PTR_ERR(entry);
+				entry = NULL;
+				break;
+			}
+		}
+
+		/* No locks are needed because used fields are immutable after
+		 * intialization.
+		 */
+		ret = isgx_vma_access_word(enclave, addr, buf, len, write,
+					   entry, i);
+		if (ret < 0)
+			break;
+	}
+
+	if (entry)
+		entry->flags &= ~ISGX_ENCLAVE_PAGE_RESERVED;
+
+	return (ret < 0 && ret != -ECANCELED) ? ret : i;
+}
+
 struct vm_operations_struct isgx_vm_ops = {
 	.close = isgx_vma_close,
 	.open = isgx_vma_open,
 	.fault = isgx_vma_fault,
+	.access = isgx_vma_access,
 };
-- 
2.7.4