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SubjectRe: [RFC PATCH 5/9] x86/sgx: Restrict mapping without an enclave page to PROT_NONE
On Fri, May 31, 2019 at 04:31:55PM -0700, Sean Christopherson wrote:
> To support LSM integration, SGX will require userspace to explicitly
> specify the allowed protections for each page. The allowed protections
> will be supplied to and modified by LSMs (based on their policies).

How the allowed protections are modified by LSMs? AFAIK they don't touch
the PROT_* flags but I could be wrong too.

> To prevent userspace from circumventing the allowed protections, do not
> allow PROT_{READ,WRITE,EXEC} mappings to an enclave without an
> associated enclave page (which will track the allowed protections).
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kernel/cpu/sgx/driver/main.c | 5 +++++
> arch/x86/kernel/cpu/sgx/encl.c | 30 +++++++++++++++++++++++++++
> arch/x86/kernel/cpu/sgx/encl.h | 3 +++
> 3 files changed, 38 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/sgx/driver/main.c b/arch/x86/kernel/cpu/sgx/driver/main.c
> index 129d356aff30..65a87c2fdf02 100644
> --- a/arch/x86/kernel/cpu/sgx/driver/main.c
> +++ b/arch/x86/kernel/cpu/sgx/driver/main.c
> @@ -63,6 +63,11 @@ static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,
> static int sgx_mmap(struct file *file, struct vm_area_struct *vma)
> {
> struct sgx_encl *encl = file->private_data;
> + int ret;
> +
> + ret = sgx_map_allowed(encl, vma->vm_start, vma->vm_end, vma->vm_flags);
> + if (ret)
> + return ret;
>
> vma->vm_ops = &sgx_vm_ops;
> vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index f23ea0fbaa47..955d4f430adc 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -235,6 +235,35 @@ static void sgx_vma_close(struct vm_area_struct *vma)
> kref_put(&encl->refcount, sgx_encl_release);
> }
>
> +int sgx_map_allowed(struct sgx_encl *encl, unsigned long start,
> + unsigned long end, unsigned long prot)

Documentation missing.

> +{
> + struct sgx_encl_page *page;
> + unsigned long addr;
> +
> + prot &= (VM_READ | VM_WRITE | VM_EXEC);
> + if (!prot || !encl)
> + return 0;
> +
> + mutex_lock(&encl->lock);
> +
> + for (addr = start; addr < end; addr += PAGE_SIZE) {
> + page = radix_tree_lookup(&encl->page_tree, addr >> PAGE_SHIFT);
> + if (!page)
> + return -EACCES;
> + }
> +
> + mutex_unlock(&encl->lock);
> +
> + return 0;
> +}
> +
> +static int sgx_vma_mprotect(struct vm_area_struct *vma, unsigned long start,
> + unsigned long end, unsigned long prot)
> +{
> + return sgx_map_allowed(vma->vm_private_data, start, end, prot);
> +}
> +
> static unsigned int sgx_vma_fault(struct vm_fault *vmf)
> {
> unsigned long addr = (unsigned long)vmf->address;
> @@ -372,6 +401,7 @@ static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
> const struct vm_operations_struct sgx_vm_ops = {
> .close = sgx_vma_close,
> .open = sgx_vma_open,
> + .mprotect = sgx_vma_mprotect,
> .fault = sgx_vma_fault,
> .access = sgx_vma_access,
> };
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index c557f0374d74..6e310e3b3fff 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -106,6 +106,9 @@ static inline unsigned long sgx_pcmd_offset(pgoff_t page_index)
> sizeof(struct sgx_pcmd);
> }
>
> +int sgx_map_allowed(struct sgx_encl *encl, unsigned long start,
> + unsigned long end, unsigned long prot);
> +
> enum sgx_encl_mm_iter {
> SGX_ENCL_MM_ITER_DONE = 0,
> SGX_ENCL_MM_ITER_NEXT = 1,
> --
> 2.21.0

This is missing explanation why it is OK to have a mismatch between
the SECINFO flags and VM_* flags. Maybe that could be explained in
sgx_map_allowed() documentation.

/Jarkko

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