Merge tag 'char-misc-5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh...

[linux-2.6-block.git] / drivers / misc / lkdtm / bugs.c

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index d9fcfd3b5af0ad27ebaaf83ed870083aa3525ffb..1606658b9b7e35ce307c25d3dcf770ef3620f6d8 100644 (file)
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -266,3 +266,69 @@ void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
 
        pr_err("FAIL: accessed page after stack!\n");
 }
+
+void lkdtm_UNSET_SMEP(void)
+{
+#ifdef CONFIG_X86_64
+#define MOV_CR4_DEPTH  64
+       void (*direct_write_cr4)(unsigned long val);
+       unsigned char *insn;
+       unsigned long cr4;
+       int i;
+
+       cr4 = native_read_cr4();
+
+       if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
+               pr_err("FAIL: SMEP not in use\n");
+               return;
+       }
+       cr4 &= ~(X86_CR4_SMEP);
+
+       pr_info("trying to clear SMEP normally\n");
+       native_write_cr4(cr4);
+       if (cr4 == native_read_cr4()) {
+               pr_err("FAIL: pinning SMEP failed!\n");
+               cr4 |= X86_CR4_SMEP;
+               pr_info("restoring SMEP\n");
+               native_write_cr4(cr4);
+               return;
+       }
+       pr_info("ok: SMEP did not get cleared\n");
+
+       /*
+        * To test the post-write pinning verification we need to call
+        * directly into the middle of native_write_cr4() where the
+        * cr4 write happens, skipping any pinning. This searches for
+        * the cr4 writing instruction.
+        */
+       insn = (unsigned char *)native_write_cr4;
+       for (i = 0; i < MOV_CR4_DEPTH; i++) {
+               /* mov %rdi, %cr4 */
+               if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
+                       break;
+               /* mov %rdi,%rax; mov %rax, %cr4 */
+               if (insn[i]   == 0x48 && insn[i+1] == 0x89 &&
+                   insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
+                   insn[i+4] == 0x22 && insn[i+5] == 0xe0)
+                       break;
+       }
+       if (i >= MOV_CR4_DEPTH) {
+               pr_info("ok: cannot locate cr4 writing call gadget\n");
+               return;
+       }
+       direct_write_cr4 = (void *)(insn + i);
+
+       pr_info("trying to clear SMEP with call gadget\n");
+       direct_write_cr4(cr4);
+       if (native_read_cr4() & X86_CR4_SMEP) {
+               pr_info("ok: SMEP removal was reverted\n");
+       } else {
+               pr_err("FAIL: cleared SMEP not detected!\n");
+               cr4 |= X86_CR4_SMEP;
+               pr_info("restoring SMEP\n");
+               native_write_cr4(cr4);
+       }
+#else
+       pr_err("FAIL: this test is x86_64-only\n");
+#endif
+}