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

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Message-Id: <20190531233159.30992-8-sean.j.christopherson@intel.com>
Date:   Fri, 31 May 2019 16:31:57 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Cedric Xing <cedric.xing@...el.com>,
        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,
        Jethro Beekman <jethro@...tanix.com>,
        Dave Hansen <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,
        Andrew Morton <akpm@...ux-foundation.org>, nhorman@...hat.com,
        npmccallum@...hat.com, Serge Ayoun <serge.ayoun@...el.com>,
        Shay Katz-zamir <shay.katz-zamir@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kai Svahn <kai.svahn@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        Kai Huang <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        William Roberts <william.c.roberts@...el.com>,
        Philip Tricca <philip.b.tricca@...el.com>
Subject: [RFC PATCH 7/9] x86/sgx: Enforce noexec filesystem restriction for enclaves

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;
+	up_read(&current->mm->mmap_sem);
+
+do_check:
+	if (prot & ~*allowed_prot)
+		return -EACCES;
+
+	return 0;
+}
+
 static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
 			     unsigned long src, struct sgx_secinfo *secinfo,
 			     unsigned int mrmask, unsigned int flags)
@@ -589,8 +610,9 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
 	BUILD_BUG_ON(SGX_SECINFO_R != VM_READ || SGX_SECINFO_W != VM_WRITE ||
 		     SGX_SECINFO_X != VM_EXEC);
 
-	if (prot & ~allowed_prot)
-		return -EACCES;
+	ret = sgx_encl_page_protect(src, prot, &allowed_prot);
+	if (ret)
+		return ret;
 
 	data_page = alloc_page(GFP_HIGHUSER);
 	if (!data_page)
-- 
2.21.0