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>

src/arch/x86/Kconfig

@@ -320,6 +320,38 @@ config MEMLAYOUT_LD_FILE
 	string
 	default "src/arch/x86/memlayout.ld"
 
+config DEBUG_HW_BREAKPOINTS
+	bool
+	default y
+	help
+	  Enable support for hardware data and instruction breakpoints through
+	  the x86 debug registers
+
+config DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES
+	bool
+	default y
+	depends on DEBUG_HW_BREAKPOINTS && IDT_IN_EVERY_STAGE
+
+config DEBUG_NULL_DEREF_BREAKPOINTS
+	bool
+	default y
+	depends on DEBUG_HW_BREAKPOINTS
+	help
+	  Enable support for catching null dereferences and instruction execution
+
+config DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES
+	bool
+	default y
+	depends on DEBUG_NULL_DEREF_BREAKPOINTS && DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES
+
+config DEBUG_NULL_DEREF_HALT
+	bool
+	default n
+	depends on DEBUG_NULL_DEREF_BREAKPOINTS
+	help
+	  When enabled null dereferences and instruction fetches will halt execution.
+	  Otherwise an error will be printed.
+
 # Some EC need an "EC firmware pointer" (a data structure hinting the address
 # of its firmware blobs) being put at a fixed position. Its space
 # (__section__(".ecfw_ptr")) should be reserved if it lies in the range of a

src/arch/x86/Makefile.inc

@@ -78,6 +78,7 @@ endef
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_X86_32)$(CONFIG_ARCH_BOOTBLOCK_X86_64),y)
 
 bootblock-y += boot.c
+bootblock-$(CONFIG_DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES) += breakpoint.c
 bootblock-y += post.c
 bootblock-y += cpu_common.c
 bootblock-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
@@ -87,6 +88,7 @@ bootblock-y += memset.c
 bootblock-y += memmove.c
 bootblock-$(CONFIG_COLLECT_TIMESTAMPS_TSC) += timestamp.c
 bootblock-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
+bootblock-$(CONFIG_DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES) += null_breakpoint.c
 bootblock-$(CONFIG_BOOTBLOCK_NORMAL) += bootblock_normal.c
 bootblock-y += gdt_init.S
 bootblock-y += id.S
@@ -122,6 +124,7 @@ ifeq ($(CONFIG_ARCH_VERSTAGE_X86_32)$(CONFIG_ARCH_VERSTAGE_X86_64),y)
 
 verstage-$(CONFIG_VBOOT_SEPARATE_VERSTAGE) += assembly_entry.S
 verstage-y += boot.c
+verstage-$(CONFIG_DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES) += breakpoint.c
 verstage-y += post.c
 verstage-$(CONFIG_VBOOT_SEPARATE_VERSTAGE) += gdt_init.S
 verstage-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
@@ -133,6 +136,7 @@ verstage-y += memset.c
 verstage-y += memcpy.c
 verstage-y += memmove.c
 verstage-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
+verstage-$(CONFIG_DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES) += null_breakpoint.c
 # If verstage is a separate stage it means there's no need
 # for a chipset-specific car_stage_entry() so use the generic one
 # which just calls verstage().
@@ -158,6 +162,7 @@ ifeq ($(CONFIG_ARCH_ROMSTAGE_X86_32)$(CONFIG_ARCH_ROMSTAGE_X86_64),y)
 
 romstage-y += assembly_entry.S
 romstage-y += boot.c
+romstage-$(CONFIG_DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES) += breakpoint.c
 romstage-y += post.c
 romstage-y += gdt_init.S
 romstage-y += cpu_common.c
@@ -167,6 +172,7 @@ romstage-y += memcpy.c
 romstage-y += memmove.c
 romstage-y += memset.c
 romstage-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
+romstage-$(CONFIG_DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES) += null_breakpoint.c
 romstage-y += postcar_loader.c
 romstage-$(CONFIG_COLLECT_TIMESTAMPS_TSC) += timestamp.c
 romstage-$(CONFIG_HAVE_CF9_RESET) += cf9_reset.c
@@ -199,6 +205,7 @@ endif
 postcar-generic-ccopts += -D__POSTCAR__
 
 postcar-y += boot.c
+postcar-$(CONFIG_DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES) += breakpoint.c
 postcar-y += post.c
 postcar-y += gdt_init.S
 postcar-y += cpu_common.c
@@ -209,6 +216,7 @@ postcar-y += memcpy.c
 postcar-y += memmove.c
 postcar-y += memset.c
 postcar-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
+postcar-$(CONFIG_DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES) += null_breakpoint.c
 postcar-y += postcar.c
 postcar-$(CONFIG_COLLECT_TIMESTAMPS_TSC) += timestamp.c
 postcar-$(CONFIG_HAVE_CF9_RESET) += cf9_reset.c
@@ -243,6 +251,7 @@ ramstage-y += c_start.S
 ramstage-y += c_exit.S
 ramstage-y += cpu.c
 ramstage-y += cpu_common.c
+ramstage-$(CONFIG_DEBUG_HW_BREAKPOINTS) += breakpoint.c
 ramstage-y += ebda.c
 ramstage-y += exception.c
 ramstage-y += idt.S
@@ -252,6 +261,7 @@ ramstage-y += memmove.c
 ramstage-y += memset.c
 ramstage-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
 ramstage-$(CONFIG_GENERATE_MP_TABLE) += mpspec.c
+ramstage-$(CONFIG_DEBUG_NULL_DEREF_BREAKPOINTS) += null_breakpoint.c
 ramstage-$(CONFIG_GENERATE_PIRQ_TABLE) += pirq_routing.c
 ramstage-y += rdrand.c
 ramstage-$(CONFIG_GENERATE_SMBIOS_TABLES) += smbios.c
@@ -306,11 +316,13 @@ $(objgenerated)/ramstage.o: $$(ramstage-objs) $(COMPILER_RT_ramstage) $$(ramstag
 
 endif # CONFIG_ARCH_RAMSTAGE_X86_32 / CONFIG_ARCH_RAMSTAGE_X86_64
 
+smm-$(CONFIG_DEBUG_HW_BREAKPOINTS_IN_ALL_STAGES) += breakpoint.c
 smm-$(CONFIG_IDT_IN_EVERY_STAGE) += exception.c
 smm-$(CONFIG_IDT_IN_EVERY_STAGE) += idt.S
 smm-y += memcpy.c
 smm-y += memmove.c
 smm-y += memset.c
 smm-$(CONFIG_X86_TOP4G_BOOTMEDIA_MAP) += mmap_boot.c
+smm-$(CONFIG_DEBUG_NULL_DEREF_BREAKPOINTS_IN_ALL_STAGES) += null_breakpoint.c
 
 smm-srcs += $(wildcard src/mainboard/$(MAINBOARDDIR)/smihandler.c)