[RFC PATCH v2 3/5] x86/sgx: Enforce noexec filesystem restriction for enclaves
From: Sean Christopherson <hidden>
Date: 2019-06-06 02:11:57
Also in:
lkml, selinux
Subsystem:
intel sgx, the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Jarkko Sakkinen, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
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. Checking noexec indirectly by way of VM_MAYEXEC naturally handles any other cases that clear VM_MAYEXEC to deny execute permissions. Signed-off-by: Sean Christopherson <redacted> --- arch/x86/kernel/cpu/sgx/driver/ioctl.c | 47 +++++++++++++++++++++++--- 1 file changed, 42 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
index ef5c2ce0f37b..44b2d73de7c3 100644
--- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c@@ -577,6 +577,44 @@ 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; + + if (!(prot & VM_EXEC)) + return 0; + + /* Hold mmap_sem across copy_from_user() to avoid a TOCTOU race. */ + down_read(¤t->mm->mmap_sem); + + vma = find_vma(current->mm, src); + if (!vma) { + ret = -EFAULT; + goto out; + } + + /* + * Query VM_MAYEXEC as an indirect path_noexec() check (see do_mmap()), + * but with some future proofing against other cases that may deny + * execute permissions. + */ + 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(¤t->mm->mmap_sem); + + return ret; +} + /** * sgx_ioc_enclave_add_page - handler for %SGX_IOC_ENCLAVE_ADD_PAGE *
@@ -616,13 +654,12 @@ static long sgx_ioc_enclave_add_page(struct file *filep, unsigned int cmd, data = kmap(data_page); - if (copy_from_user((void *)data, (void __user *)addp->src, PAGE_SIZE)) { - ret = -EFAULT; - goto out; - } - prot = addp->flags & (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)
--
2.21.0