[PATCH v4] x86/traps: Enable UBSAN traps on x86
From: Gatlin Newhouse
Date: Wed Jul 10 2024 - 16:33:09 EST
Currently ARM architectures extract which specific sanitizer
has caused a trap via encoded data in the trap instruction.
Clang on x86 currently encodes the same data in ud1 instructions
but the x86 handle_bug() and is_valid_bugaddr() functions
currently only look at ud2s.
Bring x86 to parity with arm64, similar to commit 25b84002afb9
("arm64: Support Clang UBSAN trap codes for better reporting").
Enable the reporting of UBSAN sanitizer detail on x86 architectures
compiled with clang when CONFIG_UBSAN_TRAP=y.
Signed-off-by: Gatlin Newhouse <gatlin.newhouse@xxxxxxxxx>
---
Changes in v4:
- Implement Peter's suggestions for decode_bug(), and fix
inconsistent capitalization in hex values.
Changes in v3:
- Address Thomas's remarks about: change log structure,
get_ud_type() instead of is_valid_bugaddr(), handle_bug()
changes, and handle_ubsan_failure().
Changes in v2:
- Name the new constants 'LEN_ASOP' and 'INSN_ASOP' instead of
'LEN_REX' and 'INSN_REX'
- Change handle_ubsan_failure() from enum bug_trap_type to void
function
v1: https://lore.kernel.org/linux-hardening/20240529022043.3661757-1-gatlin.newhouse@xxxxxxxxx/
v2: https://lore.kernel.org/linux-hardening/20240601031019.3708758-1-gatlin.newhouse@xxxxxxxxx/
v3: https://lore.kernel.org/linux-hardening/20240625032509.4155839-1-gatlin.newhouse@xxxxxxxxx/
---
MAINTAINERS | 2 ++
arch/x86/include/asm/bug.h | 11 +++++++
arch/x86/include/asm/ubsan.h | 23 +++++++++++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/traps.c | 57 ++++++++++++++++++++++++++++++++----
arch/x86/kernel/ubsan.c | 21 +++++++++++++
6 files changed, 110 insertions(+), 5 deletions(-)
create mode 100644 arch/x86/include/asm/ubsan.h
create mode 100644 arch/x86/kernel/ubsan.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 28e20975c26f..b8512887ffb1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -22635,6 +22635,8 @@ L: kasan-dev@xxxxxxxxxxxxxxxx
L: linux-hardening@xxxxxxxxxxxxxxx
S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
+F: arch/x86/include/asm/ubsan.h
+F: arch/x86/kernel/ubsan.c
F: Documentation/dev-tools/ubsan.rst
F: include/linux/ubsan.h
F: lib/Kconfig.ubsan
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index a3ec87d198ac..ccd573d58edb 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -13,6 +13,17 @@
#define INSN_UD2 0x0b0f
#define LEN_UD2 2
+/*
+ * In clang we have UD1s reporting UBSAN failures on X86, 64 and 32bit.
+ */
+#define INSN_ASOP 0x67
+#define OPCODE_PREFIX 0x0f
+#define OPCODE_UD1 0xb9
+#define OPCODE_UD2 0x0b
+#define BUG_NONE 0xffff
+#define BUG_UD1 0xfffe
+#define BUG_UD2 0xfffd
+
#ifdef CONFIG_GENERIC_BUG
#ifdef CONFIG_X86_32
diff --git a/arch/x86/include/asm/ubsan.h b/arch/x86/include/asm/ubsan.h
new file mode 100644
index 000000000000..ac2080984e83
--- /dev/null
+++ b/arch/x86/include/asm/ubsan.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_UBSAN_H
+#define _ASM_X86_UBSAN_H
+
+/*
+ * Clang Undefined Behavior Sanitizer trap mode support.
+ */
+#include <linux/bug.h>
+#include <linux/ubsan.h>
+#include <asm/ptrace.h>
+
+/*
+ * UBSAN uses the EAX register to encode its type in the ModRM byte.
+ */
+#define UBSAN_REG 0x40
+
+#ifdef CONFIG_UBSAN_TRAP
+void handle_ubsan_failure(struct pt_regs *regs, u16 insn);
+#else
+static inline void handle_ubsan_failure(struct pt_regs *regs, u16 insn) { return; }
+#endif /* CONFIG_UBSAN_TRAP */
+
+#endif /* _ASM_X86_UBSAN_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 74077694da7d..fe1d9db27500 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -145,6 +145,7 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += sev.o
obj-$(CONFIG_CFI_CLANG) += cfi.o
+obj-$(CONFIG_UBSAN_TRAP) += ubsan.o
obj-$(CONFIG_CALL_THUNKS) += callthunks.o
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4fa0b17e5043..b6664016622a 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -67,6 +67,7 @@
#include <asm/vdso.h>
#include <asm/tdx.h>
#include <asm/cfi.h>
+#include <asm/ubsan.h>
#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
@@ -91,6 +92,45 @@ __always_inline int is_valid_bugaddr(unsigned long addr)
return *(unsigned short *)addr == INSN_UD2;
}
+/*
+ * Check for UD1 or UD2, accounting for Address Size Override Prefixes.
+ * If it's a UD1, get the ModRM byte to pass along to UBSan.
+ */
+__always_inline int decode_bug(unsigned long addr, u32 *imm)
+{
+ u8 v;
+
+ if (addr < TASK_SIZE_MAX)
+ return BUG_NONE;
+
+ v = *(u8 *)(addr++);
+ if (v == INSN_ASOP)
+ v = *(u8 *)(addr++);
+ if (v != OPCODE_PREFIX)
+ return BUG_NONE;
+
+ v = *(u8 *)(addr++);
+ if (v == OPCODE_UD2)
+ return BUG_UD2;
+ if (v != OPCODE_UD1)
+ return BUG_NONE;
+
+ v = *(u8 *)(addr++);
+ if (X86_MODRM_RM(v) == 4)
+ addr++;
+
+ *imm = 0;
+ if (X86_MODRM_MOD(v) == 1)
+ *imm = *(u8 *)addr;
+ else if (X86_MODRM_MOD(v) == 2)
+ *imm = *(u32 *)addr;
+ else
+ WARN_ONCE(1, "Unexpected MODRM_MOD: %u\n", X86_MODRM_MOD(v));
+
+ return BUG_UD1;
+}
+
+
static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
struct pt_regs *regs, long error_code)
@@ -216,6 +256,8 @@ static inline void handle_invalid_op(struct pt_regs *regs)
static noinstr bool handle_bug(struct pt_regs *regs)
{
bool handled = false;
+ int ud_type;
+ u32 imm;
/*
* Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
@@ -223,7 +265,8 @@ static noinstr bool handle_bug(struct pt_regs *regs)
* irqentry_enter().
*/
kmsan_unpoison_entry_regs(regs);
- if (!is_valid_bugaddr(regs->ip))
+ ud_type = decode_bug(regs->ip, &imm);
+ if (ud_type == BUG_NONE)
return handled;
/*
@@ -236,10 +279,14 @@ static noinstr bool handle_bug(struct pt_regs *regs)
*/
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_enable();
- if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
- handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
- regs->ip += LEN_UD2;
- handled = true;
+ if (ud_type == BUG_UD2) {
+ if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
+ handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
+ regs->ip += LEN_UD2;
+ handled = true;
+ }
+ } else {
+ handle_ubsan_failure(regs, imm);
}
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_disable();
diff --git a/arch/x86/kernel/ubsan.c b/arch/x86/kernel/ubsan.c
new file mode 100644
index 000000000000..c90e337a1b6a
--- /dev/null
+++ b/arch/x86/kernel/ubsan.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Clang Undefined Behavior Sanitizer trap mode support.
+ */
+#include <linux/bug.h>
+#include <linux/string.h>
+#include <linux/printk.h>
+#include <linux/ubsan.h>
+#include <asm/ptrace.h>
+#include <asm/ubsan.h>
+
+/*
+ * Checks for the information embedded in the UD1 trap instruction
+ * for the UB Sanitizer in order to pass along debugging output.
+ */
+void handle_ubsan_failure(struct pt_regs *regs, u16 type)
+{
+ if ((type & 0xFF) == UBSAN_REG)
+ type >>= 8;
+ pr_crit("%s at %pS\n", report_ubsan_failure(regs, type), (void *)regs->ip);
+}
--
2.25.1