[PATCHv2 44/59] mm: Add the encrypt_mprotect() system call for MKTME

Kirill A. Shutemov
2019-07-31T15:08:36Z

From: Alison Schofield <alison.schofield@intel.com>

Implement memory encryption for MKTME (Multi-Key Total Memory
Encryption) with a new system call that is an extension of the
legacy mprotect() system call.

In encrypt_mprotect the caller must pass a handle to a previously
allocated and programmed MKTME encryption key. The key can be
obtained through the kernel key service type "mktme". The caller
must have KEY_NEED_VIEW permission on the key.

MKTME places an additional restriction on the protected data:
The length of the data must be page aligned. This is in addition
to the existing mprotect restriction that the addr must be page
aligned.

encrypt_mprotect() will lookup the hardware keyid for the given
userspace key. It will use previously defined helpers to insert
that keyid in the VMAs during legacy mprotect() execution.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
fs/exec.c | 4 +--
include/linux/mm.h | 3 +-
mm/mprotect.c | 68 +++++++++++++++++++++++++++++++++++++++++-----
3 files changed, 65 insertions(+), 10 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index c71cbfe6826a..261e81b7e3a4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -756,8 +756,8 @@ int setup_arg_pages(struct linux_binprm *bprm,
vm_flags |= mm->def_flags;
vm_flags |= VM_STACK_INCOMPLETE_SETUP;

- ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
- vm_flags);
+ ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end, vm_flags,
+ -1);
if (ret)
goto out_unlock;
BUG_ON(prev != vma);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 98a6d2bd66a6..8551b5ebdedf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1660,7 +1660,8 @@ extern unsigned long change_protection(struct vm_area_struct *vma, unsigned long
int dirty_accountable, int prot_numa);
extern int mprotect_fixup(struct vm_area_struct *vma,
struct vm_area_struct **pprev, unsigned long start,
- unsigned long end, unsigned long newflags);
+ unsigned long end, unsigned long newflags,
+ int newkeyid);

/*
* doesn't attempt to fault and will return short.
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 4d55725228e3..518d75582e7b 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -28,6 +28,7 @@
#include <linux/ksm.h>
#include <linux/uaccess.h>
#include <linux/mm_inline.h>
+#include <linux/key.h>
#include <asm/pgtable.h>
#include <asm/cacheflush.h>
#include <asm/mmu_context.h>
@@ -348,7 +349,8 @@ static int prot_none_walk(struct vm_area_struct *vma, unsigned long start,

int
mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
- unsigned long start, unsigned long end, unsigned long newflags)
+ unsigned long start, unsigned long end, unsigned long newflags,
+ int newkeyid)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long oldflags = vma->vm_flags;
@@ -358,7 +360,14 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
int error;
int dirty_accountable = 0;

- if (newflags == oldflags) {
+ /*
+ * Flags match and Keyids match or we have NO_KEY.
+ * This _fixup is usually called from do_mprotect_ext() except
+ * for one special case: caller fs/exec.c/setup_arg_pages()
+ * In that case, newkeyid is passed as -1 (NO_KEY).
+ */
+ if (newflags == oldflags &&
+ (newkeyid == vma_keyid(vma) || newkeyid == NO_KEY)) {
*pprev = vma;
return 0;
}
@@ -424,6 +433,8 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
}

success:
+ if (newkeyid != NO_KEY)
+ mprotect_set_encrypt(vma, newkeyid, start, end);
/*
* vm_flags and vm_page_prot are protected by the mmap_sem
* held in write mode.
@@ -455,10 +466,15 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
}

/*
- * When pkey==NO_KEY we get legacy mprotect behavior here.
+ * do_mprotect_ext() supports the legacy mprotect behavior plus extensions
+ * for Protection Keys and Memory Encryption Keys. These extensions are
+ * mutually exclusive and the behavior is:
+ * (pkey==NO_KEY && keyid==NO_KEY) ==> legacy mprotect
+ * (pkey is valid) ==> legacy mprotect plus Protection Key extensions
+ * (keyid is valid) ==> legacy mprotect plus Encryption Key extensions
*/
static int do_mprotect_ext(unsigned long start, size_t len,
- unsigned long prot, int pkey)
+ unsigned long prot, int pkey, int keyid)
{
unsigned long nstart, end, tmp, reqprot;
struct vm_area_struct *vma, *prev;
@@ -556,7 +572,8 @@ static int do_mprotect_ext(unsigned long start, size_t len,
tmp = vma->vm_end;
if (tmp > end)
tmp = end;
- error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
+ error = mprotect_fixup(vma, &prev, nstart, tmp, newflags,
+ keyid);
if (error)
goto out;
nstart = tmp;
@@ -581,7 +598,7 @@ static int do_mprotect_ext(unsigned long start, size_t len,
SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
unsigned long, prot)
{
- return do_mprotect_ext(start, len, prot, NO_KEY);
+ return do_mprotect_ext(start, len, prot, NO_KEY, NO_KEY);
}

#ifdef CONFIG_ARCH_HAS_PKEYS
@@ -589,7 +606,7 @@ SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
unsigned long, prot, int, pkey)
{
- return do_mprotect_ext(start, len, prot, pkey);
+ return do_mprotect_ext(start, len, prot, pkey, NO_KEY);
}

SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
@@ -638,3 +655,40 @@ SYSCALL_DEFINE1(pkey_free, int, pkey)
}

#endif /* CONFIG_ARCH_HAS_PKEYS */
+
+#ifdef CONFIG_X86_INTEL_MKTME
+
+extern int mktme_keyid_from_key(struct key *key);
+
+SYSCALL_DEFINE4(encrypt_mprotect, unsigned long, start, size_t, len,
+ unsigned long, prot, key_serial_t, serial)
+{
+ key_ref_t key_ref;
+ struct key *key;
+ int ret, keyid;
+
+ /* MKTME restriction */
+ if (!PAGE_ALIGNED(len))
+ return -EINVAL;
+
+ /*
+ * key_ref prevents the destruction of the key
+ * while the memory encryption is being set up.
+ */
+
+ key_ref = lookup_user_key(serial, 0, KEY_NEED_VIEW);
+ if (IS_ERR(key_ref))
+ return PTR_ERR(key_ref);
+
+ key = key_ref_to_ptr(key_ref);
+ keyid = mktme_keyid_from_key(key);
+ if (!keyid) {
+ key_ref_put(key_ref);
+ return -EINVAL;
+ }
+ ret = do_mprotect_ext(start, len, prot, NO_KEY, keyid);
+ key_ref_put(key_ref);
+ return ret;
+}
+
+#endif /* CONFIG_X86_INTEL_MKTME */
--
2.21.0