[RFC,v4,05/12] x86/sgx: Enforce noexec filesystem restriction for enclaves
diff mbox series

Message ID 20190619222401.14942-6-sean.j.christopherson@intel.com
State New
Headers show
Series
  • security: x86/sgx: SGX vs. LSM
Related show

Commit Message

Sean Christopherson June 19, 2019, 10:23 p.m. UTC
Do not allow an enclave page to be mapped with PROT_EXEC if the source
vma does not have VM_MAYEXEC.  This effectively enforces noexec as
do_mmap() clears VM_MAYEXEC if the vma is being loaded from a noexec
path, i.e. prevents executing a file by loading it into an enclave.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kernel/cpu/sgx/driver/ioctl.c | 42 +++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 5 deletions(-)

Comments

Jarkko Sakkinen June 21, 2019, 1:26 a.m. UTC | #1
On Wed, Jun 19, 2019 at 03:23:54PM -0700, Sean Christopherson wrote:
> Do not allow an enclave page to be mapped with PROT_EXEC if the source
> vma does not have VM_MAYEXEC.  This effectively enforces noexec as
> do_mmap() clears VM_MAYEXEC if the vma is being loaded from a noexec
> path, i.e. prevents executing a file by loading it into an enclave.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/driver/ioctl.c | 42 +++++++++++++++++++++++---
>  1 file changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> index e18d2afd2aad..1fca70a36ce3 100644
> --- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> @@ -564,6 +564,39 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
>  	return ret;
>  }
>  
> +static int sgx_encl_page_copy(void *dst, unsigned long src, unsigned long prot)

I will probably forget the context with this name after this has been
merged :-) So many functions dealing with enclave pages. Two
alternatives that come up to my mind:

1. sgx_encl_page_user_import()
2. sgx_encl_page_user_copy_from()

Not saying that they are beatiful names but at least you immediately
know the context.

> +{
> +	struct vm_area_struct *vma;
> +	int ret;
> +
> +	/* Hold mmap_sem across copy_from_user() to avoid a TOCTOU race. */
> +	down_read(&current->mm->mmap_sem);
> +
> +	/* Query vma's VM_MAYEXEC as an indirect path_noexec() check. */
> +	if (prot & PROT_EXEC) {
> +		vma = find_vma(current->mm, src);
> +		if (!vma) {
> +			ret = -EFAULT;
> +			goto out;

Should this be -EINVAL instead?

/Jarkko
Sean Christopherson July 7, 2019, 7:03 p.m. UTC | #2
On Fri, Jun 21, 2019 at 04:26:54AM +0300, Jarkko Sakkinen wrote:
> On Wed, Jun 19, 2019 at 03:23:54PM -0700, Sean Christopherson wrote:
> > Do not allow an enclave page to be mapped with PROT_EXEC if the source
> > vma does not have VM_MAYEXEC.  This effectively enforces noexec as
> > do_mmap() clears VM_MAYEXEC if the vma is being loaded from a noexec
> > path, i.e. prevents executing a file by loading it into an enclave.
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  arch/x86/kernel/cpu/sgx/driver/ioctl.c | 42 +++++++++++++++++++++++---
> >  1 file changed, 37 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> > index e18d2afd2aad..1fca70a36ce3 100644
> > --- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> > @@ -564,6 +564,39 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
> >  	return ret;
> >  }
> >  
> > +static int sgx_encl_page_copy(void *dst, unsigned long src, unsigned long prot)
> 
> I will probably forget the context with this name after this has been
> merged :-) So many functions dealing with enclave pages. Two
> alternatives that come up to my mind:
> 
> 1. sgx_encl_page_user_import()
> 2. sgx_encl_page_user_copy_from()

What about sgx_encl_page_copy_from_user() to align with copy_from_user()?
 
> Not saying that they are beatiful names but at least you immediately
> know the context.
> 
> > +{
> > +	struct vm_area_struct *vma;
> > +	int ret;
> > +
> > +	/* Hold mmap_sem across copy_from_user() to avoid a TOCTOU race. */
> > +	down_read(&current->mm->mmap_sem);
> > +
> > +	/* Query vma's VM_MAYEXEC as an indirect path_noexec() check. */
> > +	if (prot & PROT_EXEC) {
> > +		vma = find_vma(current->mm, src);
> > +		if (!vma) {
> > +			ret = -EFAULT;
> > +			goto out;
> 
> Should this be -EINVAL instead?

copy_from_user() failure is handled via -EFAULT, this is effectively an
equivalent check.

Patch
diff mbox series

diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
index e18d2afd2aad..1fca70a36ce3 100644
--- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
@@ -564,6 +564,39 @@  static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
 	return ret;
 }
 
+static int sgx_encl_page_copy(void *dst, unsigned long src, unsigned long prot)
+{
+	struct vm_area_struct *vma;
+	int ret;
+
+	/* Hold mmap_sem across copy_from_user() to avoid a TOCTOU race. */
+	down_read(&current->mm->mmap_sem);
+
+	/* Query vma's VM_MAYEXEC as an indirect path_noexec() check. */
+	if (prot & PROT_EXEC) {
+		vma = find_vma(current->mm, src);
+		if (!vma) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		if (!(vma->vm_flags & VM_MAYEXEC)) {
+			ret = -EACCES;
+			goto out;
+		}
+	}
+
+	if (copy_from_user(dst, (void __user *)src, PAGE_SIZE))
+		ret = -EFAULT;
+	else
+		ret = 0;
+
+out:
+	up_read(&current->mm->mmap_sem);
+
+	return ret;
+}
+
 /**
  * sgx_ioc_enclave_add_page - handler for %SGX_IOC_ENCLAVE_ADD_PAGE
  *
@@ -604,13 +637,12 @@  static long sgx_ioc_enclave_add_page(struct file *filep, void __user *arg)
 
 	data = kmap(data_page);
 
-	if (copy_from_user((void *)data, (void __user *)addp.src, PAGE_SIZE)) {
-		ret = -EFAULT;
-		goto out;
-	}
-
 	prot = addp.prot & (PROT_READ | PROT_WRITE | PROT_EXEC);
 
+	ret = sgx_encl_page_copy(data, addp.src, prot);
+	if (ret)
+		goto out;
+
 	ret = sgx_encl_add_page(encl, addp.addr, data, &secinfo, addp.mrmask,
 				prot);
 	if (ret)