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

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Message-ID: <CALCETrVnpFFxNr0=PB9DWqQLeuNoFaa8_iihAcxcQMNrm5ChzA@mail.gmail.com>
Date:   Tue, 4 Jun 2019 13:26:06 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     "Xing, Cedric" <cedric.xing@...el.com>
Cc:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        "Tricca, Philip B" <philip.b.tricca@...el.com>
Subject: Re: [RFC PATCH 7/9] x86/sgx: Enforce noexec filesystem restriction
 for enclaves

On Sun, Jun 2, 2019 at 11:29 PM Xing, Cedric <cedric.xing@...el.com> wrote:
>
> > 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 <sean.j.christopherson@...el.com>
> > ---
> >  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.