[PATCH] arm64: Support Clang UBSAN trap codes for better reporting

Kees Cook
2023-02-02T22:37:18Z

On arm64, Clang encodes the UBSAN check type in the esr. Extract this
and actually report UBSAN traps with some specificity when building with
CONFIG_UBSAN_TRAP. Before:

Internal error: BRK handler: 00000000f20003e8 [#1] PREEMPT SMP

After:

Internal error: UBSAN: shift out of bounds: 00000000f2005514 [#1] PREEMPT SMP

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: John Stultz <jstultz@google.com>
Cc: Yongqin Liu <yongqin.liu@linaro.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm64/include/asm/brk-imm.h | 2 ++
arch/arm64/kernel/traps.c | 21 +++++++++++++
include/linux/ubsan.h | 9 ++++++
lib/Makefile | 2 --
lib/ubsan.c | 54 ++++++++++++++++++++++++++++++++
lib/ubsan.h | 28 +++++++++++++++++
6 files changed, 114 insertions(+), 2 deletions(-)
create mode 100644 include/linux/ubsan.h

diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index 6e000113e508..3f0f0d03268b 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -28,6 +28,8 @@
#define BUG_BRK_IMM 0x800
#define KASAN_BRK_IMM 0x900
#define KASAN_BRK_MASK 0x0ff
+#define UBSAN_BRK_IMM 0x5500
+#define UBSAN_BRK_MASK 0x00ff

#define CFI_BRK_IMM_TARGET GENMASK(4, 0)
#define CFI_BRK_IMM_TYPE GENMASK(9, 5)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 4c0caa589e12..87f42eb1c950 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -26,6 +26,7 @@
#include <linux/syscalls.h>
#include <linux/mm_types.h>
#include <linux/kasan.h>
+#include <linux/ubsan.h>
#include <linux/cfi.h>

#include <asm/atomic.h>
@@ -1074,6 +1075,19 @@ static struct break_hook kasan_break_hook = {
};
#endif

+#ifdef CONFIG_UBSAN_TRAP
+static int ubsan_handler(struct pt_regs *regs, unsigned long esr)
+{
+ die(report_ubsan_failure(regs, esr & UBSAN_BRK_MASK), regs, esr);
+ return DBG_HOOK_HANDLED;
+}
+
+static struct break_hook ubsan_break_hook = {
+ .fn = ubsan_handler,
+ .imm = UBSAN_BRK_IMM,
+ .mask = UBSAN_BRK_MASK,
+};
+#endif

#define esr_comment(esr) ((esr) & ESR_ELx_BRK64_ISS_COMMENT_MASK)

@@ -1091,6 +1105,10 @@ int __init early_brk64(unsigned long addr, unsigned long esr,
#ifdef CONFIG_KASAN_SW_TAGS
if ((esr_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
+#endif
+#ifdef CONFIG_UBSAN_TRAP
+ if ((esr_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
+ return ubsan_handler(regs, esr) != DBG_HOOK_HANDLED;
#endif
return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
}
@@ -1104,6 +1122,9 @@ void __init trap_init(void)
register_kernel_break_hook(&fault_break_hook);
#ifdef CONFIG_KASAN_SW_TAGS
register_kernel_break_hook(&kasan_break_hook);
+#endif
+#ifdef CONFIG_UBSAN_TRAP
+ register_kernel_break_hook(&ubsan_break_hook);
#endif
debug_traps_init();
}
diff --git a/include/linux/ubsan.h b/include/linux/ubsan.h
new file mode 100644
index 000000000000..bff7445498de
--- /dev/null
+++ b/include/linux/ubsan.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_UBSAN_H
+#define _LINUX_UBSAN_H
+
+#ifdef CONFIG_UBSAN_TRAP
+const char *report_ubsan_failure(struct pt_regs *regs, u32 check_type);
+#endif
+
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index 4d9461bfea42..81b988bf9448 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -340,9 +340,7 @@ quiet_cmd_build_OID_registry = GEN $@
clean-files += oid_registry_data.c

obj-$(CONFIG_UCS2_STRING) += ucs2_string.o
-ifneq ($(CONFIG_UBSAN_TRAP),y)
obj-$(CONFIG_UBSAN) += ubsan.o
-endif

UBSAN_SANITIZE_ubsan.o := n
KASAN_SANITIZE_ubsan.o := n
diff --git a/lib/ubsan.c b/lib/ubsan.c
index 60c7099857a0..98a671ec56e9 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -18,6 +18,58 @@

#include "ubsan.h"

+#ifdef CONFIG_UBSAN_TRAP
+const char *report_ubsan_failure(struct pt_regs *regs, u32 check_type)
+{
+ switch (check_type) {
+ case ubsan_add_overflow:
+ return "UBSAN: addition overflow";
+ case ubsan_builtin_unreachable:
+ return "UBSAN: unreachable code";
+ case ubsan_cfi_check_fail:
+ return "UBSAN: CFI failure";
+ case ubsan_divrem_overflow:
+ return "UBSAN: divide/remainder overflow";
+ case ubsan_function_type_mismatch:
+ return "UBSAN: function type mismatch";
+ case ubsan_implicit_conversion:
+ return "UBSAN: implicit conversion";
+ case ubsan_invalid_builtin:
+ return "UBSAN: invalid builtin";
+ case ubsan_invalid_objc_cast:
+ return "UBSAN: invalid object cast";
+ case ubsan_load_invalid_value:
+ return "UBSAN: loading invalid value";
+ case ubsan_missing_return:
+ return "UBSAN: missing return";
+ case ubsan_mul_overflow:
+ return "UBSAN: multiplication overflow";
+ case ubsan_negate_overflow:
+ return "UBSAN: negation overflow";
+ case ubsan_nonnull_arg:
+ return "UBSAN: non-NULL argument";
+ case ubsan_nonnull_return:
+ return "UBSAN: non-NULL return";
+ case ubsan_out_of_bounds:
+ return "UBSAN: array index out of bounds";
+ case ubsan_pointer_overflow:
+ return "UBSAN: pointer overflow";
+ case ubsan_shift_out_of_bounds:
+ return "UBSAN: shift out of bounds";
+ case ubsan_sub_overflow:
+ return "UBSAN: subtraction overflow";
+ case ubsan_type_mismatch:
+ return "UBSAN: type mismatch";
+ case ubsan_alignment_assumption:
+ return "UBSAN: alignment assumption";
+ case ubsan_vla_bound_not_positive:
+ return "UBSAN: VLA bounds not positive";
+ default:
+ return "UBSAN: unknown failure";
+ }
+}
+
+#else
static const char * const type_check_kinds[] = {
"load of",
"store to",
@@ -384,3 +436,5 @@ void __ubsan_handle_alignment_assumption(void *_data, unsigned long ptr,
ubsan_epilogue();
}
EXPORT_SYMBOL(__ubsan_handle_alignment_assumption);
+
+#endif /* !CONFIG_UBSAN_TRAP */
diff --git a/lib/ubsan.h b/lib/ubsan.h
index 9a0b71c5ff9f..9c7f00f550f5 100644
--- a/lib/ubsan.h
+++ b/lib/ubsan.h
@@ -2,6 +2,34 @@
#ifndef _LIB_UBSAN_H
#define _LIB_UBSAN_H

+enum ubsan_checks {
+ ubsan_add_overflow,
+ ubsan_builtin_unreachable,
+ ubsan_cfi_check_fail,
+ ubsan_divrem_overflow,
+ ubsan_dynamic_type_cache_miss,
+ ubsan_float_cast_overflow,
+ ubsan_function_type_mismatch,
+ ubsan_implicit_conversion,
+ ubsan_invalid_builtin,
+ ubsan_invalid_objc_cast,
+ ubsan_load_invalid_value,
+ ubsan_missing_return,
+ ubsan_mul_overflow,
+ ubsan_negate_overflow,
+ ubsan_nullability_arg,
+ ubsan_nullability_return,
+ ubsan_nonnull_arg,
+ ubsan_nonnull_return,
+ ubsan_out_of_bounds,
+ ubsan_pointer_overflow,
+ ubsan_shift_out_of_bounds,
+ ubsan_sub_overflow,
+ ubsan_type_mismatch,
+ ubsan_alignment_assumption,
+ ubsan_vla_bound_not_positive,
+};
+
enum {
type_kind_int = 0,
type_kind_float = 1,
--
2.34.1