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.newho...@gmail.com> --- 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.newho...@gmail.com/ v2: https://lore.kernel.org/linux-hardening/20240601031019.3708758-1-gatlin.newho...@gmail.com/ v3: https://lore.kernel.org/linux-hardening/20240625032509.4155839-1-gatlin.newho...@gmail.com/ --- 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-...@googlegroups.com L: linux-hardening@vger.kernel.org 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