Re: [RFC PATCH 7/9] x86/sgx: Enforce noexec filesystem restriction for enclaves

On Sun, Jun 2, 2019 at 11:29 PM Xing, Cedric [off-list ref] wrote:

quoted

From: Christopherson, Sean J
Sent: Friday, May 31, 2019 4:32 PM

Do not allow an enclave page to be mapped with PROT_EXEC if the source page is backed by a
file on a noexec file system.

Signed-off-by: Sean Christopherson <redacted>
---
 arch/x86/kernel/cpu/sgx/driver/ioctl.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c

b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
index c30acd3fbbdd..5f71be7cbb01 100644

--- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c

@@ -576,6 +576,27 @@ static int __sgx_encl_add_page(struct sgx_encl *encl, unsigned long

addr,
      return ret;
 }

+static int sgx_encl_page_protect(unsigned long src, unsigned long prot,
+                              unsigned long *allowed_prot)
+{
+     struct vm_area_struct *vma;
+
+     if (!(*allowed_prot & VM_EXEC))
+             goto do_check;
+
+     down_read(&current->mm->mmap_sem);
+     vma = find_vma(current->mm, src);
+     if (!vma || (vma->vm_file && path_noexec(&vma->vm_file->f_path)))
+             *allowed_prot &= ~VM_EXEC;

Testing (vma->vm_flags & VM_MAYEXEC) == 0 should be a better approach.

I think I agree, although that would need a comment explaining why it works.