x86/sgx: Add ptrace() support for the SGX driver

Enclave memory is normally inaccessible from outside the enclave. This
makes enclaves hard to debug. However, enclaves can be put in a debug
mode when they are being built. In that mode, enclave data *can* be read
and/or written by using the ENCLS[EDBGRD] and ENCLS[EDBGWR] functions.

This is obviously only for debugging and destroys all the protections
present with normal enclaves. But, enclaves know their own debug status
and can adjust their behavior appropriately.

Add a vm_ops->access() implementation which can be used to read and write
memory inside debug enclaves.  This is typically used via ptrace() APIs.

 [ bp: Massage. ]

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Jethro Beekman <jethro@fortanix.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-23-jarkko@kernel.org

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index b74dadf85989a4ce14d0f6db8169ff89a4ca3e53..ee50a501027712f3ede1a7c9bfabd910d2500623 100644 (file)
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -272,10 +272,121 @@ static int sgx_vma_mprotect(struct vm_area_struct *vma, unsigned long start,
        return sgx_encl_may_map(vma->vm_private_data, start, end, newflags);
 }
 
+static int sgx_encl_debug_read(struct sgx_encl *encl, struct sgx_encl_page *page,
+                              unsigned long addr, void *data)
+{
+       unsigned long offset = addr & ~PAGE_MASK;
+       int ret;
+
+
+       ret = __edbgrd(sgx_get_epc_virt_addr(page->epc_page) + offset, data);
+       if (ret)
+               return -EIO;
+
+       return 0;
+}
+
+static int sgx_encl_debug_write(struct sgx_encl *encl, struct sgx_encl_page *page,
+                               unsigned long addr, void *data)
+{
+       unsigned long offset = addr & ~PAGE_MASK;
+       int ret;
+
+       ret = __edbgwr(sgx_get_epc_virt_addr(page->epc_page) + offset, data);
+       if (ret)
+               return -EIO;
+
+       return 0;
+}
+
+/*
+ * Load an enclave page to EPC if required, and take encl->lock.
+ */
+static struct sgx_encl_page *sgx_encl_reserve_page(struct sgx_encl *encl,
+                                                  unsigned long addr,
+                                                  unsigned long vm_flags)
+{
+       struct sgx_encl_page *entry;
+
+       for ( ; ; ) {
+               mutex_lock(&encl->lock);
+
+               entry = sgx_encl_load_page(encl, addr, vm_flags);
+               if (PTR_ERR(entry) != -EBUSY)
+                       break;
+
+               mutex_unlock(&encl->lock);
+       }
+
+       if (IS_ERR(entry))
+               mutex_unlock(&encl->lock);
+
+       return entry;
+}
+
+static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
+                         void *buf, int len, int write)
+{
+       struct sgx_encl *encl = vma->vm_private_data;
+       struct sgx_encl_page *entry = NULL;
+       char data[sizeof(unsigned long)];
+       unsigned long align;
+       int offset;
+       int cnt;
+       int ret = 0;
+       int i;
+
+       /*
+        * If process was forked, VMA is still there but vm_private_data is set
+        * to NULL.
+        */
+       if (!encl)
+               return -EFAULT;
+
+       if (!test_bit(SGX_ENCL_DEBUG, &encl->flags))
+               return -EFAULT;
+
+       for (i = 0; i < len; i += cnt) {
+               entry = sgx_encl_reserve_page(encl, (addr + i) & PAGE_MASK,
+                                             vma->vm_flags);
+               if (IS_ERR(entry)) {
+                       ret = PTR_ERR(entry);
+                       break;
+               }
+
+               align = ALIGN_DOWN(addr + i, sizeof(unsigned long));
+               offset = (addr + i) & (sizeof(unsigned long) - 1);
+               cnt = sizeof(unsigned long) - offset;
+               cnt = min(cnt, len - i);
+
+               ret = sgx_encl_debug_read(encl, entry, align, data);
+               if (ret)
+                       goto out;
+
+               if (write) {
+                       memcpy(data + offset, buf + i, cnt);
+                       ret = sgx_encl_debug_write(encl, entry, align, data);
+                       if (ret)
+                               goto out;
+               } else {
+                       memcpy(buf + i, data + offset, cnt);
+               }
+
+out:
+               mutex_unlock(&encl->lock);
+
+               if (ret)
+                       break;
+       }
+
+       return ret < 0 ? ret : i;
+}
+
 const struct vm_operations_struct sgx_vm_ops = {
        .fault = sgx_vma_fault,
        .mprotect = sgx_vma_mprotect,
        .open = sgx_vma_open,
+       .access = sgx_vma_access,
 };
 
 /**