linux-kernel - Re: [PATCH v24 12/24] x86/sgx: Linux Enclave Driver

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Date:   Mon, 9 Dec 2019 21:08:29 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Haitao Huang <haitao.huang@...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, sean.j.christopherson@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.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>
Subject: Re: [PATCH v24 12/24] x86/sgx: Linux Enclave Driver

On Mon, Dec 02, 2019 at 09:48:43AM -0600, Haitao Huang wrote:
> On Fri, 29 Nov 2019 17:13:14 -0600, Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> 
> 
> > +
> > +	for (c = 0 ; c < addp.length; c += PAGE_SIZE) {
> > +		if (signal_pending(current)) {
> > +			ret = -ERESTARTSYS;
> > +			break;
> > +		}
> 
> This IOC is not idempotent as pages EADDed at this point can not be
> re-EADDed again. So we can't return ERESTARTSYS

Agreed, should be -EINTR.

I added these entries to the v25 change log based on your recent
reports:

* Fix a double-free issue when SGX_IOC_ENCLAVE_ADD_PAGES
  fails on executing ENCLS[EADD]. The rollback path executed
  radix_tree_delete() on the same address twice when this happened.
  [fixes v24, reported by Haitao]
* Return -EINTR instead of -ERESTARTSYS in SGX_IOC_ENCLAVE_ADD_PAGES when
  a signal is pending [fixes v23, reported by Haitao]

The master branch [1] has been updated accordingly. There is also a
tag v24 for looking up easily what has overally changed e.g.

$ git --no-pager diff v24..master
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index ab9e48cd294b..5c9e6e161698 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -413,13 +413,8 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
 
 	ret = __sgx_encl_add_page(encl, encl_page, epc_page, secinfo,
 				  src);
-	if (ret) {
-		/* ENCLS failure. */
-		if (ret == -EIO)
-			sgx_encl_destroy(encl);
-
+	if (ret)
 		goto err_out;
-	}
 
 	/*
 	 * Complete the "add" before doing the "extend" so that the "add"
@@ -432,17 +427,11 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
 
 	if (flags & SGX_PAGE_MEASURE) {
 		ret = __sgx_encl_extend(encl, epc_page);
-
-		/* ENCLS failure. */
-		if (ret) {
-			sgx_encl_destroy(encl);
-			goto out_unlock;
-		}
+		if (ret)
+			goto err_out;
 	}
 
 	sgx_mark_page_reclaimable(encl_page->epc_page);
-
-out_unlock:
 	mutex_unlock(&encl->lock);
 	up_read(&current->mm->mmap_sem);
 	return ret;
@@ -460,6 +449,13 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
 	sgx_free_page(epc_page);
 	kfree(encl_page);
 
+	/*
+	 * Destroy enclave on ENCLS failure as this means that EPC has been
+	 * invalidated.
+	 */
+	if (ret == -EIO)
+		sgx_encl_destroy(encl);
+
 	return ret;
 }
 
@@ -536,7 +532,7 @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void __user *arg)
 
 	for (c = 0 ; c < addp.length; c += PAGE_SIZE) {
 		if (signal_pending(current)) {
-			ret = -ERESTARTSYS;
+			ret = -EINTR;
 			break;
 		}

[1] https://github.com/jsakkine-intel/linux-sgx

/Jarkko