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Date:   Thu, 29 Apr 2021 02:20:50 -0500
From:   "Christopher M. Riedl" <cmr@...escreens.de>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     linux-hardening@...r.kernel.org, x86@...nel.org,
        tglx@...utronix.de, keescook@...omium.org
Subject: [PATCH v4 04/11] lkdtm/x86_64: Add test to hijack a patch mapping

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 <cmr@...escreens.de>
---
 drivers/misc/lkdtm/perms.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index c6f96ebffccfd..55c3bec6d3b72 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.
  */
@@ -233,28 +233,51 @@ static void patching_target(void)
 	return;
 }
 
+#ifdef CONFIG_PPC
 #include <asm/code-patching.h>
 struct ppc_inst * const patch_site = (struct ppc_inst *)&patching_target;
+#endif
+
+#ifdef CONFIG_X86_64
+#include <asm/text-patching.h>
+u32 * const patch_site = (u32 *)&patching_target;
+#endif
 
 static inline int lkdtm_do_patch(u32 data)
 {
+#ifdef CONFIG_PPC
 	return patch_instruction(patch_site, ppc_inst(data));
+#endif
+#ifdef CONFIG_X86_64
+	text_poke(patch_site, &data, sizeof(u32));
+	return 0;
+#endif
 }
 
 static inline u32 lkdtm_read_patch_site(void)
 {
+#ifdef CONFIG_PPC
 	struct ppc_inst inst = READ_ONCE(*patch_site);
 	return ppc_inst_val(ppc_inst_read(&inst));
+#endif
+#ifdef CONFIG_X86_64
+	return READ_ONCE(*patch_site);
+#endif
 }
 
 /* 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)
@@ -347,8 +370,8 @@ 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

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