linux-kernel - [PATCH] x86/sgx: Add SGX_PAGE_REPEAT flag for SGX_IOC_ENCLAVE_ADD

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Date:   Thu, 10 Jun 2021 10:21:17 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     linux-sgx@...r.kernel.org
Cc:     Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/sgx: Add SGX_PAGE_REPEAT flag for SGX_IOC_ENCLAVE_ADD_PAGES

For uninitialized data, there's a need to add the same page multiple times,
e.g. a zero page, instead of traversing the source memory forward. With the
current API, this requires to call SGX_IOC_ENCLAVE_ADD_PAGES multiple
times, once per page, which is not very efficient.

Add a new SGX_PAGE_REPEAT flag to resolve the issue. When this flag is set
to the 'flags' field of struct sgx_enclave_pages, the ioctl will apply the
page at 'src' multiple times, instead of moving forward in the address
space.

Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
 arch/x86/include/uapi/asm/sgx.h | 3 +++
 arch/x86/kernel/cpu/sgx/ioctl.c | 9 +++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
index 9690d6899ad9..d20fd54fa250 100644
--- a/arch/x86/include/uapi/asm/sgx.h
+++ b/arch/x86/include/uapi/asm/sgx.h
@@ -12,9 +12,12 @@
  * enum sgx_page_flags - page control flags
  * %SGX_PAGE_MEASURE:	Measure the page contents with a sequence of
  *			ENCLS[EEXTEND] operations.
+ * %SGX_PAGE_REPEAT:	Read the same page at 'src' multiple times,
+ *			instead of traversing the memory forward.
  */
 enum sgx_page_flags {
 	SGX_PAGE_MEASURE	= 0x01,
+	SGX_PAGE_REPEAT		= 0x02,
 };
 
 #define SGX_MAGIC 0xA4
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 83df20e3e633..d81bb257bad0 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -415,6 +415,7 @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void __user *arg)
 {
 	struct sgx_enclave_add_pages add_arg;
 	struct sgx_secinfo secinfo;
+	unsigned long src;
 	unsigned long c;
 	int ret;
 
@@ -453,8 +454,12 @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void __user *arg)
 		if (need_resched())
 			cond_resched();
 
-		ret = sgx_encl_add_page(encl, add_arg.src + c, add_arg.offset + c,
-					&secinfo, add_arg.flags);
+		if (add_arg.flags & SGX_PAGE_REPEAT)
+			src = add_arg.src;
+		else
+			src = add_arg.src + c;
+
+		ret = sgx_encl_add_page(encl, src, add_arg.offset + c, &secinfo, add_arg.flags);
 		if (ret)
 			break;
 	}
-- 
2.31.1