On Thu, Jan 28, 2021, ira.weiny@xxxxxxxxx wrote:
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> ---
> 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
>
