linux-kernel - [tip: x86/sgx] x86/sgx: Remove unnecessary kmap() from sgx_ioc_enclave

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Date:   Thu, 25 Mar 2021 09:07:53 -0000
From:   "tip-bot2 for Ira Weiny" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>, Borislav Petkov <bp@...e.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/sgx] x86/sgx: Remove unnecessary kmap() from sgx_ioc_enclave_init()

The following commit has been merged into the x86/sgx branch of tip:

Commit-ID:     633b0616cfe085679471a4c0fae02e8c3a1a9866
Gitweb:        https://git.kernel.org/tip/633b0616cfe085679471a4c0fae02e8c3a1a9866
Author:        Ira Weiny <ira.weiny@...el.com>
AuthorDate:    Wed, 24 Mar 2021 11:22:46 -07:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Thu, 25 Mar 2021 09:50:32 +01:00

x86/sgx: Remove unnecessary kmap() from sgx_ioc_enclave_init()

kmap() is inefficient and is being replaced by kmap_local_page(), if
possible. There is no readily apparent reason why initp_page needs to be
allocated and kmap'ed() except that 'sigstruct' needs to be page-aligned
and 'token' 512 byte-aligned.

Rather than change it to kmap_local_page(), use kmalloc() instead
because kmalloc() can give this alignment when allocating PAGE_SIZE
bytes.

Remove the alloc_page()/kmap() and replace with kmalloc(PAGE_SIZE, ...)
to get a page aligned kernel address.

In addition, add a comment to document the alignment requirements so that
others don't attempt to 'fix' this again.

 [ bp: Massage commit message. ]

Signed-off-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20210324182246.2484875-1-ira.weiny@intel.com
---
 arch/x86/kernel/cpu/sgx/ioctl.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 90a5caf..2e10367 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -604,7 +604,6 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
 {
 	struct sgx_sigstruct *sigstruct;
 	struct sgx_enclave_init init_arg;
-	struct page *initp_page;
 	void *token;
 	int ret;
 
@@ -615,11 +614,15 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
 	if (copy_from_user(&init_arg, arg, sizeof(init_arg)))
 		return -EFAULT;
 
-	initp_page = alloc_page(GFP_KERNEL);
-	if (!initp_page)
+	/*
+	 * 'sigstruct' must be on a page boundary and 'token' on a 512 byte
+	 * boundary.  kmalloc() will give this alignment when allocating
+	 * PAGE_SIZE bytes.
+	 */
+	sigstruct = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!sigstruct)
 		return -ENOMEM;
 
-	sigstruct = kmap(initp_page);
 	token = (void *)((unsigned long)sigstruct + PAGE_SIZE / 2);
 	memset(token, 0, SGX_LAUNCH_TOKEN_SIZE);
 
@@ -645,8 +648,7 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
 	ret = sgx_encl_init(encl, sigstruct, token);
 
 out:
-	kunmap(initp_page);
-	__free_page(initp_page);
+	kfree(sigstruct);
 	return ret;
 }