[PATCH v1] lkdtm/bugs: fix build error in lkdtm_UNSET_SMEP

[Brendan Higgins <brendanhiggins@google.com>]

When building ARCH=um with CONFIG_UML_X86=y and CONFIG_64BIT=y we get
the build errors:

drivers/misc/lkdtm/bugs.c: In function ‘lkdtm_UNSET_SMEP’:
drivers/misc/lkdtm/bugs.c:288:8: error: implicit declaration of function ‘native_read_cr4’ [-Werror=implicit-function-declaration]
  cr4 = native_read_cr4();
        ^~~~~~~~~~~~~~~
drivers/misc/lkdtm/bugs.c:290:13: error: ‘X86_CR4_SMEP’ undeclared (first use in this function); did you mean ‘X86_FEATURE_SMEP’?
  if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
             ^~~~~~~~~~~~
             X86_FEATURE_SMEP
drivers/misc/lkdtm/bugs.c:290:13: note: each undeclared identifier is reported only once for each function it appears in
drivers/misc/lkdtm/bugs.c:297:2: error: implicit declaration of function ‘native_write_cr4’; did you mean ‘direct_write_cr4’? [-Werror=implicit-function-declaration]
  native_write_cr4(cr4);
  ^~~~~~~~~~~~~~~~
  direct_write_cr4

So specify that this block of code should only build when
CONFIG_X86_64=y *AND* CONFIG_UML is unset.

Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
---

This patch is part of my larger effort to get allyesconfig closer to
working for ARCH=um. For more information about that, checkout the cover
letter for a related patchset here:

https://lore.kernel.org/lkml/20191211192742.95699-1-brendanhiggins@google.com/

---
 drivers/misc/lkdtm/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index a4fdad04809a9..6c1aab177fced 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -278,7 +278,7 @@ void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
 
 void lkdtm_UNSET_SMEP(void)
 {
-#ifdef CONFIG_X86_64
+#if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML)
 #define MOV_CR4_DEPTH	64
 	void (*direct_write_cr4)(unsigned long val);
 	unsigned char *insn;
-- 
2.24.1.735.g03f4e72817-goog