linux-kernel - Re: [PATCH v30 10/20] x86/sgx: Linux Enclave Driver

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Date:   Fri, 22 May 2020 22:39:14 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, nhorman@...hat.com, npmccallum@...hat.com,
        haitao.huang@...el.com, andriy.shevchenko@...ux.intel.com,
        tglx@...utronix.de, kai.svahn@...el.com, bp@...en8.de,
        josh@...htriplett.org, luto@...nel.org, kai.huang@...el.com,
        rientjes@...gle.com, cedric.xing@...el.com, puiterwijk@...hat.com,
        linux-security-module@...r.kernel.org,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Chunyang Hui <sanqian.hcy@...fin.com>,
        Jordan Hand <jorhand@...ux.microsoft.com>,
        Seth Moore <sethmo@...gle.com>
Subject: Re: [PATCH v30 10/20] x86/sgx: Linux Enclave Driver

On Thu, May 21, 2020 at 12:12:36PM -0700, Sean Christopherson wrote:
> On Fri, May 15, 2020 at 03:44:00AM +0300, Jarkko Sakkinen wrote:
> > +long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> > +{
> > +	struct sgx_encl *encl = filep->private_data;
> > +	int ret, encl_flags;
> > +
> > +	encl_flags = atomic_fetch_or(SGX_ENCL_IOCTL, &encl->flags);
> > +	if (encl_flags & SGX_ENCL_IOCTL)
> > +		return -EBUSY;
> > +
> > +	if (encl_flags & SGX_ENCL_DEAD)
> > +		return -EFAULT;
> 
> Returning immediately is wrong as it leaves SGX_ENCL_IOCTL set.  This results
> in the application seeing -EBUSY on future ioctls() instead of -EFAULT.  Can be
> fixed as below.  Do you want me to send a formal patch on linux-sgx?
> 
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 77757a74644d..df35a79e915c 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -751,8 +751,10 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
>         if (encl_flags & SGX_ENCL_IOCTL)
>                 return -EBUSY;
> 
> -       if (encl_flags & SGX_ENCL_DEAD)
> -               return -EFAULT;
> +       if (encl_flags & SGX_ENCL_DEAD) {
> +               ret = -EFAULT;
> +               goto out;
> +       }
> 
>         switch (cmd) {
>         case SGX_IOC_ENCLAVE_CREATE:
> @@ -772,6 +774,7 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
>                 break;
>         }
> 
> +out:
>         atomic_andnot(SGX_ENCL_IOCTL, &encl->flags);
> 
>         return ret;
> 
> 
> > +
> > +	switch (cmd) {
> > +	case SGX_IOC_ENCLAVE_CREATE:
> > +		ret = sgx_ioc_enclave_create(encl, (void __user *)arg);
> > +		break;
> > +	case SGX_IOC_ENCLAVE_ADD_PAGES:
> > +		ret = sgx_ioc_enclave_add_pages(encl, (void __user *)arg);
> > +		break;
> > +	case SGX_IOC_ENCLAVE_INIT:
> > +		ret = sgx_ioc_enclave_init(encl, (void __user *)arg);
> > +		break;
> > +	default:
> > +		ret = -ENOIOCTLCMD;
> > +		break;
> > +	}
> > +
> > +	atomic_andnot(SGX_ENCL_IOCTL, &encl->flags);
> > +
> > +	return ret;
> > +}

Thanks. Fixed in my tree:

v31:
* Unset SGX_ENCL_IOCTL in the error path of checking encl->flags in order
  to prevent leaving it set, and thus block any further ioctl calls.
* Added missing cleanup_srcu_struct() call to sgx_encl_release().
* Take encl->lock in sgx_encl_add_page() in order to prevent races with
  the page reclaimer.

 /Jarkko