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Date: Mon, 1 Feb 2021 17:37:25 -0800
From: ira.weiny@...el.com
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Ira Weiny <ira.weiny@...el.com>,
Sean Christopherson <seanjc@...gle.com>,
Jethro Beekman <jethro@...tanix.com>,
linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org
Subject: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
From: Ira Weiny <ira.weiny@...el.com>
kmap is inefficient and we are trying to reduce the usage in the kernel.
There is no readily apparent reason why the initp_page page needs to be
allocated and kmap'ed() but sigstruct needs to be page aligned and token
512 byte aligned.
In this case page_address() can be used instead of kmap_local_page() as
a much more efficient way to use the address because the page is
allocated GFP_KERNEL.
Remove the kmap and replace with page_address() to get a kernel address
for the alloc'ed page.
In addition add a comment regarding the alignment requirements as well
as 2 BUILD_BUG_ON's to ensure future changes to sigstruct and token do
not go unnoticed and cause a bug.
Cc: Sean Christopherson <seanjc@...gle.com>,
Cc: Jethro Beekman <jethro@...tanix.com>,
Signed-off-by: Ira Weiny <ira.weiny@...el.com>
---
Changes from v1[1]:
Use page_address() instead of kcmalloc() to ensure sigstruct is
page aligned
Use BUILD_BUG_ON to ensure token and sigstruct don't collide.
[1] https://lore.kernel.org/lkml/20210129001459.1538805-1-ira.weiny@intel.com/
---
arch/x86/kernel/cpu/sgx/ioctl.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 90a5caf76939..678b02d67c3c 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -615,11 +615,18 @@ 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;
+ /*
+ * sigstruct must be on a page boundry and token on a 512 byte boundry
+ * so use alloc_page/page_address instead of a kmalloc().
+ */
initp_page = alloc_page(GFP_KERNEL);
if (!initp_page)
return -ENOMEM;
- sigstruct = kmap(initp_page);
+ sigstruct = page_address(initp_page);
+
+ BUILD_BUG_ON(sizeof(*sigstruct) > (PAGE_SIZE/2));
+ BUILD_BUG_ON(SGX_LAUNCH_TOKEN_SIZE > (PAGE_SIZE/2));
token = (void *)((unsigned long)sigstruct + PAGE_SIZE / 2);
memset(token, 0, SGX_LAUNCH_TOKEN_SIZE);
@@ -645,7 +652,6 @@ 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);
return ret;
}
--
2.28.0.rc0.12.gb6a658bd00c9
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