From: Peter Zijlstra peterz@infradead.org
[ Upstream commit c20ad96c9a8f0aeaf4e4057730a22de2657ad0c2 ]
Notably, don't attempt to decode an immediate when MOD == 3.
Additionally have it return the instruction length, such that WARN like bugs can more reliably skip to the correct instruction.
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Sami Tolvanen samitolvanen@google.com Link: https://lore.kernel.org/r/20250207122546.721120726@infradead.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/bug.h | 5 ++- arch/x86/include/asm/ibt.h | 4 +- arch/x86/kernel/traps.c | 82 ++++++++++++++++++++++++++++---------- 3 files changed, 65 insertions(+), 26 deletions(-)
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h index 806649c7f23dc..9a0f29be1a9ea 100644 --- a/arch/x86/include/asm/bug.h +++ b/arch/x86/include/asm/bug.h @@ -22,8 +22,9 @@ #define SECOND_BYTE_OPCODE_UD2 0x0b
#define BUG_NONE 0xffff -#define BUG_UD1 0xfffe -#define BUG_UD2 0xfffd +#define BUG_UD2 0xfffe +#define BUG_UD1 0xfffd +#define BUG_UD1_UBSAN 0xfffc
#ifdef CONFIG_GENERIC_BUG
diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h index 1e59581d500ca..b778ae6e67ee8 100644 --- a/arch/x86/include/asm/ibt.h +++ b/arch/x86/include/asm/ibt.h @@ -41,7 +41,7 @@ _ASM_PTR fname "\n\t" \ ".popsection\n\t"
-static inline __attribute_const__ u32 gen_endbr(void) +static __always_inline __attribute_const__ u32 gen_endbr(void) { u32 endbr;
@@ -56,7 +56,7 @@ static inline __attribute_const__ u32 gen_endbr(void) return endbr; }
-static inline __attribute_const__ u32 gen_endbr_poison(void) +static __always_inline __attribute_const__ u32 gen_endbr_poison(void) { /* * 4 byte NOP that isn't NOP4 (in fact it is OSP NOP3), such that it diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d8d9bc5a9b328..8718d58dd0fbe 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -92,10 +92,17 @@ __always_inline int is_valid_bugaddr(unsigned long addr)
/* * 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. + * If it's a UD1, further decode to determine its use: + * + * UBSan{0}: 67 0f b9 00 ud1 (%eax),%eax + * UBSan{10}: 67 0f b9 40 10 ud1 0x10(%eax),%eax + * static_call: 0f b9 cc ud1 %esp,%ecx + * + * Notably UBSAN uses EAX, static_call uses ECX. */ -__always_inline int decode_bug(unsigned long addr, u32 *imm) +__always_inline int decode_bug(unsigned long addr, s32 *imm, int *len) { + unsigned long start = addr; u8 v;
if (addr < TASK_SIZE_MAX) @@ -108,24 +115,42 @@ __always_inline int decode_bug(unsigned long addr, u32 *imm) return BUG_NONE;
v = *(u8 *)(addr++); - if (v == SECOND_BYTE_OPCODE_UD2) + if (v == SECOND_BYTE_OPCODE_UD2) { + *len = addr - start; return BUG_UD2; + }
- if (!IS_ENABLED(CONFIG_UBSAN_TRAP) || v != SECOND_BYTE_OPCODE_UD1) + if (v != SECOND_BYTE_OPCODE_UD1) return BUG_NONE;
- /* Retrieve the immediate (type value) for the UBSAN UD1 */ - 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)); + v = *(u8 *)(addr++); /* ModRM */ + + if (X86_MODRM_MOD(v) != 3 && X86_MODRM_RM(v) == 4) + addr++; /* SIB */ + + /* Decode immediate, if present */ + switch (X86_MODRM_MOD(v)) { + case 0: if (X86_MODRM_RM(v) == 5) + addr += 4; /* RIP + disp32 */ + break; + + case 1: *imm = *(s8 *)addr; + addr += 1; + break; + + case 2: *imm = *(s32 *)addr; + addr += 4; + break; + + case 3: break; + } + + /* record instruction length */ + *len = addr - start; + + if (X86_MODRM_REG(v) == 0) /* EAX */ + return BUG_UD1_UBSAN;
return BUG_UD1; } @@ -256,10 +281,10 @@ 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; + int ud_type, ud_len; + s32 ud_imm;
- ud_type = decode_bug(regs->ip, &imm); + ud_type = decode_bug(regs->ip, &ud_imm, &ud_len); if (ud_type == BUG_NONE) return handled;
@@ -279,15 +304,28 @@ static noinstr bool handle_bug(struct pt_regs *regs) */ if (regs->flags & X86_EFLAGS_IF) raw_local_irq_enable(); - if (ud_type == BUG_UD2) { + + switch (ud_type) { + case BUG_UD2: if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN || handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) { - regs->ip += LEN_UD2; + regs->ip += ud_len; handled = true; } - } else if (IS_ENABLED(CONFIG_UBSAN_TRAP)) { - pr_crit("%s at %pS\n", report_ubsan_failure(regs, imm), (void *)regs->ip); + break; + + case BUG_UD1_UBSAN: + if (IS_ENABLED(CONFIG_UBSAN_TRAP)) { + pr_crit("%s at %pS\n", + report_ubsan_failure(regs, ud_imm), + (void *)regs->ip); + } + break; + + default: + break; } + if (regs->flags & X86_EFLAGS_IF) raw_local_irq_disable(); instrumentation_end();