lkdtm: Make arch-specific tests always available

I'd like arch-specific tests to XFAIL when on a mismatched architecture
so that we can more easily compare test coverage across all systems.
Lacking kernel configs or CPU features count as a FAIL, not an XFAIL.

Additionally fixes a build failure under 32-bit UML.

Fixes: b09511c2 ("lkdtm: Add a DOUBLE_FAULT crash type on x86")
Fixes: cea23efb ("lkdtm/bugs: Make double-fault test always available")
Fixes: 6cb6982f ("lkdtm: arm64: test kernel pointer authentication")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200625203704.317097-5-keescook@chromium.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/lkdtm/bugs.c

@@ -13,7 +13,7 @@
 #include <linux/uaccess.h>
 #include <linux/slab.h>
 
-#ifdef CONFIG_X86_32
+#if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
 #include <asm/desc.h>
 #endif
 
@@ -418,7 +418,7 @@ void lkdtm_UNSET_SMEP(void)
 
 void lkdtm_DOUBLE_FAULT(void)
 {
-#ifdef CONFIG_X86_32
+#if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML)
 	/*
 	 * Trigger #DF by setting the stack limit to zero.  This clobbers
 	 * a GDT TLS slot, which is okay because the current task will die
@@ -453,38 +453,42 @@ void lkdtm_DOUBLE_FAULT(void)
 #endif
 }
 
-#ifdef CONFIG_ARM64_PTR_AUTH
+#ifdef CONFIG_ARM64
 static noinline void change_pac_parameters(void)
 {
+	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) {
 		/* Reset the keys of current task */
 		ptrauth_thread_init_kernel(current);
 		ptrauth_thread_switch_kernel(current);
+	}
 }
+#endif
 
-#define CORRUPT_PAC_ITERATE	10
 noinline void lkdtm_CORRUPT_PAC(void)
 {
+#ifdef CONFIG_ARM64
+#define CORRUPT_PAC_ITERATE	10
 	int i;
 
+	if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH))
+		pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH\n");
+
 	if (!system_supports_address_auth()) {
-		pr_err("FAIL: arm64 pointer authentication feature not present\n");
+		pr_err("FAIL: CPU lacks pointer authentication feature\n");
 		return;
 	}
 
-	pr_info("Change the PAC parameters to force function return failure\n");
+	pr_info("changing PAC parameters to force function return failure...\n");
 	/*
-	 * Pac is a hash value computed from input keys, return address and
+	 * PAC is a hash value computed from input keys, return address and
 	 * stack pointer. As pac has fewer bits so there is a chance of
 	 * collision, so iterate few times to reduce the collision probability.
 	 */
 	for (i = 0; i < CORRUPT_PAC_ITERATE; i++)
 		change_pac_parameters();
 
-	pr_err("FAIL: %s test failed. Kernel may be unstable from here\n", __func__);
-}
-#else /* !CONFIG_ARM64_PTR_AUTH */
-noinline void lkdtm_CORRUPT_PAC(void)
-{
-	pr_err("FAIL: arm64 pointer authentication config disabled\n");
-}
+	pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n");
+#else
+	pr_err("XFAIL: this test is arm64-only\n");
 #endif
+}

drivers/misc/lkdtm/lkdtm.h

@@ -31,9 +31,7 @@ void lkdtm_CORRUPT_USER_DS(void);
 void lkdtm_STACK_GUARD_PAGE_LEADING(void);
 void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
 void lkdtm_UNSET_SMEP(void);
-#ifdef CONFIG_X86_32
 void lkdtm_DOUBLE_FAULT(void);
-#endif
 void lkdtm_CORRUPT_PAC(void);
 
 /* lkdtm_heap.c */

tools/testing/selftests/lkdtm/tests.txt

@@ -14,6 +14,7 @@ STACK_GUARD_PAGE_LEADING
 STACK_GUARD_PAGE_TRAILING
 UNSET_SMEP CR4 bits went missing
 DOUBLE_FAULT
+CORRUPT_PAC
 UNALIGNED_LOAD_STORE_WRITE
 #OVERWRITE_ALLOCATION Corrupts memory on failure
 #WRITE_AFTER_FREE Corrupts memory on failure