[PATCH 5/7] x86/sgx: Add flag to zero added region instead of copying from source

[Sean Christopherson <sean.j.christopherson@xxxxxxxxx>]

For some enclaves, e.g. an enclave with a small code footprint and a
large working set, the vast majority of pages added to the enclave are
zero pages.  Introduce a flag to denote such zero pages.  The major
benefit of the flag will be realized in a future patch to use Linux's
actual zero page as the source, as opposed to explicitly zeroing the
enclave's backing memory.

Use bit 8 for the SGX_ZERO_REGION flag to avoid an anticipated conflict
with passing PROT_{READ,WRITE,EXEC} in bits 2:0, and to leave room in
case there is a need for additional protection related bits.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/include/uapi/asm/sgx.h        |  5 +++++
 arch/x86/kernel/cpu/sgx/driver/ioctl.c | 15 ++++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
index 30d114f6b3bd..18204722f238 100644
--- a/arch/x86/include/uapi/asm/sgx.h
+++ b/arch/x86/include/uapi/asm/sgx.h
@@ -31,6 +31,9 @@ struct sgx_enclave_create  {
 	__u64	src;
 };
 
+/* Zero an added region instead of copying data from a source page. */
+#define SGX_ZERO_REGION	0x100
+
 /**
  * struct sgx_enclave_add_region - parameter structure for the
  *                                 %SGX_IOC_ENCLAVE_ADD_REGION ioctl
@@ -38,6 +41,7 @@ struct sgx_enclave_create  {
  * @src:	start address for the pages' data
  * @size:	size of region, in bytes
  * @secinfo:	address of the SECINFO data (common to the entire region)
+ * @flags:	miscellaneous flags
  * @mrmask:	bitmask of 256 byte chunks to measure (applied per 4k page)
  */
 struct sgx_enclave_add_region {
@@ -45,6 +49,7 @@ struct sgx_enclave_add_region {
 	__u64	src;
 	__u64	size;
 	__u64	secinfo;
+	__u32	flags;
 	__u16	mrmask;
 } __attribute__((__packed__));
 
diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
index b69350696b87..c35264ea0c93 100644
--- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
@@ -459,6 +459,9 @@ static int sgx_validate_tcs(struct sgx_encl *encl, struct sgx_tcs *tcs)
 {
 	int i;
 
+	if (!tcs)
+		return -EINVAL;
+
 	if (tcs->flags & SGX_TCS_RESERVED_MASK)
 		return -EINVAL;
 
@@ -510,7 +513,10 @@ static int sgx_encl_queue_page(struct sgx_encl *encl,
 	}
 
 	backing_ptr = kmap(backing);
-	memcpy(backing_ptr, data, PAGE_SIZE);
+	if (data)
+		memcpy(backing_ptr, data, PAGE_SIZE);
+	else
+		memset(backing_ptr, 0, PAGE_SIZE);
 	kunmap(backing);
 	if (page_type == SGX_SECINFO_TCS)
 		encl_page->desc |= SGX_ENCL_PAGE_TCS;
@@ -576,12 +582,15 @@ static int __sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
 
 static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
 			     unsigned long src, struct sgx_secinfo *secinfo,
-			     unsigned int mrmask)
+			     unsigned int mrmask, unsigned long flags)
 {
 	struct page *data_page;
 	void *data;
 	int ret;
 
+	if (flags & SGX_ZERO_REGION)
+		return __sgx_encl_add_page(encl, addr, NULL, secinfo, mrmask);
+
 	data_page = alloc_page(GFP_HIGHUSER);
 	if (!data_page)
 		return -ENOMEM;
@@ -658,7 +667,7 @@ static long sgx_ioc_enclave_add_region(struct file *filep, void __user *arg)
 			cond_resched();
 
 		ret = sgx_encl_add_page(encl, region.addr + i, region.src + i,
-					&secinfo, region.mrmask);
+					&secinfo, region.mrmask, region.flags);
 		if (ret)
 			break;
 	}
-- 
2.21.0