* [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
@ 2021-01-29 0:14 ira.weiny
2021-01-29 17:37 ` Sean Christopherson
0 siblings, 1 reply; 7+ messages in thread
From: ira.weiny @ 2021-01-29 0:14 UTC (permalink / raw)
To: Jarkko Sakkinen; +Cc: Ira Weiny, linux-kernel, linux-sgx
From: Ira Weiny <ira.weiny@intel.com>
There is no reason to alloc a page and kmap it to store this temporary
data from the user. This is especially true when we are trying to
remove kmap usages. Also placing the token pointer 1/2 way into the
page is fragile.
Replace this allocation with two kzalloc()'s which also removes the need
for the memset().
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
arch/x86/kernel/cpu/sgx/ioctl.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 90a5caf76939..9c9019760585 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;
@@ -615,13 +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 = kzalloc(sizeof(*sigstruct), 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);
+ token = kzalloc(SGX_LAUNCH_TOKEN_SIZE, GFP_KERNEL);
+ if (!token) {
+ ret = -ENOMEM;
+ goto free_sigstruct;
+ }
if (copy_from_user(sigstruct, (void __user *)init_arg.sigstruct,
sizeof(*sigstruct))) {
@@ -645,8 +646,9 @@ 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(token);
+free_sigstruct:
+ kfree(sigstruct);
return ret;
}
--
2.28.0.rc0.12.gb6a658bd00c9
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
2021-01-29 0:14 [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init() ira.weiny
@ 2021-01-29 17:37 ` Sean Christopherson
2021-02-01 8:48 ` Christoph Hellwig
0 siblings, 1 reply; 7+ messages in thread
From: Sean Christopherson @ 2021-01-29 17:37 UTC (permalink / raw)
To: ira.weiny; +Cc: Jarkko Sakkinen, linux-kernel, linux-sgx
On Thu, Jan 28, 2021, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> There is no reason to alloc a page and kmap it to store this temporary
> data from the user.
Actually, there is, it's just poorly documented. The sigstruct needs to be
page aligned, and the token needs to be 512-byte aligned. kmcalloc doesn't
guarantee alignment. IIRC things will work until slub_debug is enabled, at
which point the natural alignment behavior goes out the window.
> This is especially true when we are trying to
> remove kmap usages. Also placing the token pointer 1/2 way into the
> page is fragile.
>
> Replace this allocation with two kzalloc()'s which also removes the need
> for the memset().
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> arch/x86/kernel/cpu/sgx/ioctl.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 90a5caf76939..9c9019760585 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;
>
> @@ -615,13 +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 = kzalloc(sizeof(*sigstruct), 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);
> + token = kzalloc(SGX_LAUNCH_TOKEN_SIZE, GFP_KERNEL);
> + if (!token) {
> + ret = -ENOMEM;
> + goto free_sigstruct;
> + }
>
> if (copy_from_user(sigstruct, (void __user *)init_arg.sigstruct,
> sizeof(*sigstruct))) {
> @@ -645,8 +646,9 @@ 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(token);
> +free_sigstruct:
> + kfree(sigstruct);
> return ret;
> }
>
> --
> 2.28.0.rc0.12.gb6a658bd00c9
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
2021-01-29 17:37 ` Sean Christopherson
@ 2021-02-01 8:48 ` Christoph Hellwig
2021-02-02 17:37 ` Jarkko Sakkinen
0 siblings, 1 reply; 7+ messages in thread
From: Christoph Hellwig @ 2021-02-01 8:48 UTC (permalink / raw)
To: Sean Christopherson; +Cc: ira.weiny, Jarkko Sakkinen, linux-kernel, linux-sgx
On Fri, Jan 29, 2021 at 09:37:30AM -0800, Sean Christopherson wrote:
> On Thu, Jan 28, 2021, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> >
> > There is no reason to alloc a page and kmap it to store this temporary
> > data from the user.
>
> Actually, there is, it's just poorly documented. The sigstruct needs to be
> page aligned, and the token needs to be 512-byte aligned. kmcalloc doesn't
> guarantee alignment. IIRC things will work until slub_debug is enabled, at
> which point the natural alignment behavior goes out the window.
Well, there still is absolutely no need for the kmap as you can use
page_address for a GFP_KERNEL allocation.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
2021-02-01 8:48 ` Christoph Hellwig
@ 2021-02-02 17:37 ` Jarkko Sakkinen
0 siblings, 0 replies; 7+ messages in thread
From: Jarkko Sakkinen @ 2021-02-02 17:37 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Sean Christopherson, ira.weiny, linux-kernel, linux-sgx
On Mon, Feb 01, 2021 at 08:48:12AM +0000, Christoph Hellwig wrote:
> On Fri, Jan 29, 2021 at 09:37:30AM -0800, Sean Christopherson wrote:
> > On Thu, Jan 28, 2021, ira.weiny@intel.com wrote:
> > > From: Ira Weiny <ira.weiny@intel.com>
> > >
> > > There is no reason to alloc a page and kmap it to store this temporary
> > > data from the user.
> >
> > Actually, there is, it's just poorly documented. The sigstruct needs to be
> > page aligned, and the token needs to be 512-byte aligned. kmcalloc doesn't
> > guarantee alignment. IIRC things will work until slub_debug is enabled, at
> > which point the natural alignment behavior goes out the window.
>
> Well, there still is absolutely no need for the kmap as you can use
> page_address for a GFP_KERNEL allocation.
Yeah, we do that in sgx_ioc_enclave_create already based on feedback:
secs = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!secs)
return -ENOMEM;
The kmap() in sgx_ioc_enclave_init() is an unfortunate miss. Let's just
follow the pre-existing pattern.
/Jarkko
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
@ 2021-02-02 1:37 ira.weiny
2021-02-02 18:55 ` Dave Hansen
0 siblings, 1 reply; 7+ messages in thread
From: ira.weiny @ 2021-02-02 1:37 UTC (permalink / raw)
To: Jarkko Sakkinen
Cc: Ira Weiny, Sean Christopherson, Jethro Beekman, linux-kernel, linux-sgx
From: Ira Weiny <ira.weiny@intel.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@google.com>,
Cc: Jethro Beekman <jethro@fortanix.com>,
Signed-off-by: Ira Weiny <ira.weiny@intel.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
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
2021-02-02 1:37 ira.weiny
@ 2021-02-02 18:55 ` Dave Hansen
2021-02-02 22:43 ` Jarkko Sakkinen
0 siblings, 1 reply; 7+ messages in thread
From: Dave Hansen @ 2021-02-02 18:55 UTC (permalink / raw)
To: ira.weiny, Jarkko Sakkinen
Cc: Sean Christopherson, Jethro Beekman, linux-kernel, linux-sgx
On 2/1/21 5:37 PM, ira.weiny@intel.com wrote:
> 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.
Hi Ira,
It's a *relatively* recent guaranteed, but:
https://www.kernel.org/doc/Documentation/core-api/memory-allocation.rst
says:
> The address of a chunk allocated with `kmalloc` is aligned to at least
> ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the
> alignment is also guaranteed to be at least the respective size.
So, if you allocate a page with kmalloc(), you get an aligned page. Yay!
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
2021-02-02 18:55 ` Dave Hansen
@ 2021-02-02 22:43 ` Jarkko Sakkinen
0 siblings, 0 replies; 7+ messages in thread
From: Jarkko Sakkinen @ 2021-02-02 22:43 UTC (permalink / raw)
To: Dave Hansen
Cc: ira.weiny, Sean Christopherson, Jethro Beekman, linux-kernel, linux-sgx
On Tue, Feb 02, 2021 at 10:55:36AM -0800, Dave Hansen wrote:
> On 2/1/21 5:37 PM, ira.weiny@intel.com wrote:
> > 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.
>
> Hi Ira,
>
> It's a *relatively* recent guaranteed, but:
>
> https://www.kernel.org/doc/Documentation/core-api/memory-allocation.rst
>
> says:
>
> > The address of a chunk allocated with `kmalloc` is aligned to at least
> > ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the
> > alignment is also guaranteed to be at least the respective size.
>
> So, if you allocate a page with kmalloc(), you get an aligned page. Yay!
And this what we do sgx_ioc_enclave_create() anyway, as I stated in my
earlier response. Better to use the same pattern everywhere consitently
when it makes sense.
/Jarkko
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-02-02 22:44 UTC | newest]
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2021-01-29 0:14 [PATCH] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init() ira.weiny
2021-01-29 17:37 ` Sean Christopherson
2021-02-01 8:48 ` Christoph Hellwig
2021-02-02 17:37 ` Jarkko Sakkinen
2021-02-02 1:37 ira.weiny
2021-02-02 18:55 ` Dave Hansen
2021-02-02 22:43 ` Jarkko Sakkinen
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