2021-01-18 13:42:06

by Tianjia Zhang

Subject: [PATCH] x86/sgx: Remove redundant if conditions in sgx_encl_create

In this scenario, there is no case where va_page is NULL, and
the error has been checked. The if condition statement here is
redundant, so remove the condition detection.

Reported-by: Jia Zhang <[email protected]>
Signed-off-by: Tianjia Zhang <[email protected]>
---
arch/x86/kernel/cpu/sgx/ioctl.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 90a5caf76939..f45957c05f69 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -66,9 +66,8 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
va_page = sgx_encl_grow(encl);
if (IS_ERR(va_page))
return PTR_ERR(va_page);
- else if (va_page)
- list_add(&va_page->list, &encl->va_pages);
- /* else the tail page of the VA page list had free slots. */
+
+ list_add(&va_page->list, &encl->va_pages);

/* The extra page goes to SECS. */
encl_size = secs->size + PAGE_SIZE;
--
2.19.1.3.ge56e4f7

2021-01-19 20:32:15

by Sean Christopherson

Subject: Re: [PATCH] x86/sgx: Remove redundant if conditions in sgx_encl_create

On Mon, Jan 18, 2021, Tianjia Zhang wrote:
> In this scenario, there is no case where va_page is NULL, and
> the error has been checked. The if condition statement here is
> redundant, so remove the condition detection.
>
> Reported-by: Jia Zhang <[email protected]>
> Signed-off-by: Tianjia Zhang <[email protected]>
> ---
> arch/x86/kernel/cpu/sgx/ioctl.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 90a5caf76939..f45957c05f69 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -66,9 +66,8 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
> va_page = sgx_encl_grow(encl);
> if (IS_ERR(va_page))
> return PTR_ERR(va_page);
> - else if (va_page)
> - list_add(&va_page->list, &encl->va_pages);
> - /* else the tail page of the VA page list had free slots. */
> +
> + list_add(&va_page->list, &encl->va_pages);

Maybe add a WARN_ONCE to document/enforce the behavior?

va_page = sgx_encl_grow(encl);
if (IS_ERR(va_page))
return PTR_ERR(va_page);

if (WARN_ONCE(!va_page, "clever comment goes here))
return -EIO;

list_add(&va_page->list, &encl->va_pages);

>
> /* The extra page goes to SECS. */
> encl_size = secs->size + PAGE_SIZE;
> --
> 2.19.1.3.ge56e4f7
>

2021-01-20 14:50:17

by Jarkko Sakkinen

Subject: Re: [PATCH] x86/sgx: Remove redundant if conditions in sgx_encl_create

On Mon, Jan 18, 2021 at 09:33:58PM +0800, Tianjia Zhang wrote:
> In this scenario, there is no case where va_page is NULL, and
> the error has been checked. The if condition statement here is
> redundant, so remove the condition detection.
>
> Reported-by: Jia Zhang <[email protected]>
> Signed-off-by: Tianjia Zhang <[email protected]>

What do we gain with this change and why is it reported as a
regression?

/Jarkko

> ---
> arch/x86/kernel/cpu/sgx/ioctl.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 90a5caf76939..f45957c05f69 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -66,9 +66,8 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
> va_page = sgx_encl_grow(encl);
> if (IS_ERR(va_page))
> return PTR_ERR(va_page);
> - else if (va_page)
> - list_add(&va_page->list, &encl->va_pages);
> - /* else the tail page of the VA page list had free slots. */
> +
> + list_add(&va_page->list, &encl->va_pages);
>
> /* The extra page goes to SECS. */
> encl_size = secs->size + PAGE_SIZE;
> --
> 2.19.1.3.ge56e4f7
>
>