From 25b84002afb9dc9a91a7ea67166879c13ad82422 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Thu, 2 Feb 2023 22:07:49 +0000
Subject: arm64: Support Clang UBSAN trap codes for better reporting

When building with CONFIG_UBSAN_TRAP=y on arm64, Clang encodes the UBSAN
check (handler) type in the esr. Extract this and actually report these
traps as coming from the specific UBSAN check that tripped.

Before:

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

After:

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

Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Yongqin Liu <yongqin.liu@linaro.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
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 |  3 +++
 arch/arm64/kernel/traps.c        | 21 +++++++++++++++++++++
 2 files changed, 24 insertions(+)

(limited to 'arch/arm64')

diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index 6e000113e508..1abdcd508a11 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -17,6 +17,7 @@
  * 0x401: for compile time BRK instruction
  * 0x800: kernel-mode BUG() and WARN() traps
  * 0x9xx: tag-based KASAN trap (allowed values 0x900 - 0x9ff)
+ * 0x55xx: Undefined Behavior Sanitizer traps ('U' << 8)
  * 0x8xxx: Control-Flow Integrity traps
  */
 #define KPROBES_BRK_IMM			0x004
@@ -28,6 +29,8 @@
 #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();
 }
-- 
cgit