arch/x86: Add support for catching null dereferences through debug regs

This commit adds support for catching null dereferences and execution
through x86's debug registers. This is particularly useful when running
32-bit coreboot as paging is not enabled to catch these through page
faults. This commit adds three new configs to support this feature:
DEBUG_HW_BREAKPOINTS, DEBUG_NULL_DEREF_BREAKPOINTS and
DEBUG_NULL_DEREF_HALT.

BUG=b:223902046
TEST=Ran on nipperkin device, verifying that HW breakpoints work as
expected.

Change-Id: I113590689046a13c2a552741bbfe7668a834354a
Signed-off-by: Robert Zieba <robertzieba@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63657
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

2 files changed, 74 insertions, 0 deletions

diff --git a/src/arch/x86/include/arch/breakpoint.h b/src/arch/x86/include/arch/breakpoint.h
new file mode 100644
index 0000000000..32e9f48d09
--- /dev/null
+++ b/src/arch/x86/include/arch/breakpoint.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _BREAKPOINT_H_
+#define _BREAKPOINT_H_
+
+#include <arch/registers.h>
+#include <types.h>
+
+#if CONFIG(DEBUG_HW_BREAKPOINTS) && \
+	(CONFIG(DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES) || ENV_RAMSTAGE)
+struct breakpoint_handle {
+	int bp;
+};
+
+typedef int (*breakpoint_handler)(struct breakpoint_handle, struct eregs *info);
+
+enum breakpoint_result {
+	BREAKPOINT_RES_OK = 0,
+	BREAKPOINT_RES_NONE_AVAILABLE = -1,
+	BREAKPOINT_RES_INVALID_HANDLE = -2,
+	BREAKPOINT_RES_INVALID_LENGTH = -3
+};
+
+enum breakpoint_type {
+	BREAKPOINT_TYPE_INSTRUCTION = 0x0,
+	BREAKPOINT_TYPE_DATA_WRITE = 0x1,
+	BREAKPOINT_TYPE_IO = 0x2,
+	BREAKPOINT_TYPE_DATA_RW = 0x3,
+};
+
+/* Creates an instruction breakpoint at the given address. */
+enum breakpoint_result breakpoint_create_instruction(struct breakpoint_handle *out_handle,
+						     void *virt_addr);
+/* Creates a data breakpoint at the given address for len bytes. */
+enum breakpoint_result breakpoint_create_data(struct breakpoint_handle *out_handle,
+					      void *virt_addr, size_t len, bool write_only);
+/* Removes a given breakpoint. */
+enum breakpoint_result breakpoint_remove(struct breakpoint_handle handle);
+/* Enables or disables a given breakpoint. */
+enum breakpoint_result breakpoint_enable(struct breakpoint_handle handle, bool enabled);
+/* Returns the type of a breakpoint. */
+enum breakpoint_result breakpoint_get_type(struct breakpoint_handle handle,
+					   enum breakpoint_type *type);
+/*
+ * Sets a handler function to be called when the breakpoint is hit. The handler should return 0
+ * to continue or any other value to halt execution as a fatal error.
+ */
+enum breakpoint_result breakpoint_set_handler(struct breakpoint_handle handle,
+					      breakpoint_handler handler);
+/* Called by x86_exception to dispatch breakpoint exceptions to the correct handler. */
+int breakpoint_dispatch_handler(struct eregs *info);
+#else
+static inline int breakpoint_dispatch_handler(struct eregs *info)
+{
+	/* Not implemented */
+	return 0;
+}
+#endif
+#endif /* _BREAKPOINT_H_ */
diff --git a/src/arch/x86/include/arch/null_breakpoint.h b/src/arch/x86/include/arch/null_breakpoint.h
new file mode 100644
index 0000000000..bc86dc03e4
--- /dev/null
+++ b/src/arch/x86/include/arch/null_breakpoint.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _NULL_BREAKPOINT_H_
+#define _NULL_BREAKPOINT_H_
+
+#if CONFIG(DEBUG_NULL_DEREF_BREAKPOINTS) && \
+    (CONFIG(DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES) || ENV_RAMSTAGE)
+
+/* Places data and instructions breakpoints at address zero. */
+void null_breakpoint_init(void);
+#else
+static inline void null_breakpoint_init(void)
+{
+    /* Not implemented */
+}
+#endif
+#endif /* _NULL_BREAKPOINT_H_ */