arch/x86: Add function to check for unmodified ectx

This can be used in situtations where the executed code must not touch
the extended registers. For example, interrupt handlers in Unikraft do
save these and therefore also cannot modify them. Doing so is usually
breaking the interrupted code.

Signed-off-by: Marco Schlumpp <marco@unikraft.io>

arch/x86/ectx.c

@@ -40,6 +40,7 @@
 #include <uk/essentials.h>
 #include <uk/assert.h>
 #include <uk/print.h>
+#include <uk/hexdump.h>
 #include <string.h> /* memset */
 
 enum x86_save_method {
@@ -173,3 +174,28 @@ void ukarch_ectx_load(struct ukarch_ectx *state)
 		break;
 	}
 }
+
+#ifdef CONFIG_ARCH_X86_64
+void ukarch_ectx_assert_equal(struct ukarch_ectx *state)
+{
+	__u8 ectxbuf[ectx_size + ectx_align];
+	struct ukarch_ectx *current;
+
+	/* Store the current state */
+	current = (struct ukarch_ectx *)ALIGN_UP((__uptr)ectxbuf, ectx_align);
+	ukarch_ectx_init(current);
+
+	if (memcmp(current, state, ectx_size) != 0) {
+		uk_pr_crit("Modified ECTX detected!\n");
+		uk_pr_crit("Current:\n");
+		uk_hexdumpk(KLVL_CRIT, current, ectx_size,
+			    UK_HXDF_ADDR | UK_HXDF_GRPQWORD | UK_HXDF_COMPRESS,
+			    2);
+
+		uk_pr_crit("Expected:\n");
+		uk_hexdumpk(KLVL_CRIT, state, ectx_size,
+			    UK_HXDF_ADDR | UK_HXDF_GRPQWORD | UK_HXDF_COMPRESS,
+			    2);
+	}
+}
+#endif

include/uk/arch/ctx.h

@@ -231,5 +231,16 @@ void ukarch_ectx_store(struct ukarch_ectx *state);
  */
 void ukarch_ectx_load(struct ukarch_ectx *state);
 
+#ifdef CONFIG_ARCH_X86_64
+/**
+ * Compare the given extended context with the state of the currently executing
+ * CPU. If the state is different, crash the kernel.
+ *
+ * @param state
+ *   Reference to extended context to compare to
+ */
+void ukarch_ectx_assert_equal(struct ukarch_ectx *state);
+#endif
+
 #endif /* !__ASSEMBLY__ */
 #endif /* __UKARCH_CTX_H__ */