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

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Date:   Thu, 21 May 2020 12:12:36 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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 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;
> +}