Subject: [PATCH v5 4/8] lkdtm/x86_64: Add test to hijack a patch mapping

From: "Christopher M. Riedl" <[email-masked]>
Date: Tue, 13 Jul 2021 00:31:09 -0500

A previous commit implemented an LKDTM test on powerpc to exploit the
temporary mapping established when patching code with STRICT_KERNEL_RWX
enabled. Extend the test to work on x86_64 as well.

Signed-off-by: Christopher M. Riedl <[email-masked]>
---
 drivers/misc/lkdtm/perms.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 39e7456852229..41e87e5f9cc86 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -224,7 +224,7 @@ void lkdtm_ACCESS_NULL(void)
 }
 
 #if (IS_BUILTIN(CONFIG_LKDTM) && defined(CONFIG_STRICT_KERNEL_RWX) && \
-	defined(CONFIG_PPC))
+	(defined(CONFIG_PPC) || defined(CONFIG_X86_64)))
 /*
  * This is just a dummy location to patch-over.
  */
@@ -233,12 +233,25 @@ static void patching_target(void)
 	return;
 }
 
-#include <asm/code-patching.h>
 const u32 *patch_site = (const u32 *)&patching_target;
 
+#ifdef CONFIG_PPC
+#include <asm/code-patching.h>
+#endif
+
+#ifdef CONFIG_X86_64
+#include <asm/text-patching.h>
+#endif
+
 static inline int lkdtm_do_patch(u32 data)
 {
+#ifdef CONFIG_PPC
 	return patch_instruction((u32 *)patch_site, ppc_inst(data));
+#endif
+#ifdef CONFIG_X86_64
+	text_poke((void *)patch_site, &data, sizeof(u32));
+	return 0;
+#endif
 }
 
 static inline u32 lkdtm_read_patch_site(void)
@@ -249,11 +262,16 @@ static inline u32 lkdtm_read_patch_site(void)
 /* Returns True if the write succeeds */
 static inline bool lkdtm_try_write(u32 data, u32 *addr)
 {
+#ifdef CONFIG_PPC
 	__put_kernel_nofault(addr, &data, u32, err);
 	return true;
 
 err:
 	return false;
+#endif
+#ifdef CONFIG_X86_64
+	return !__put_user(data, addr);
+#endif
 }
 
 static int lkdtm_patching_cpu(void *data)
@@ -346,8 +364,8 @@ void lkdtm_HIJACK_PATCH(void)
 
 void lkdtm_HIJACK_PATCH(void)
 {
-	if (!IS_ENABLED(CONFIG_PPC))
-		pr_err("XFAIL: this test only runs on powerpc\n");
+	if (!IS_ENABLED(CONFIG_PPC) && !IS_ENABLED(CONFIG_X86_64))
+		pr_err("XFAIL: this test only runs on powerpc and x86_64\n");
 	if (!IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
 		pr_err("XFAIL: this test requires CONFIG_STRICT_KERNEL_RWX\n");
 	if (!IS_BUILTIN(CONFIG_LKDTM))
-- 
2.26.1