linux-kernel - [PATCH v4 03/10] x86/traps: Decode 0xEA #UD

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Message-ID: <20250224124200.166774696@infradead.org>
Date: Mon, 24 Feb 2025 13:37:06 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
 peterz@...radead.org,
 alyssa.milburn@...el.com,
 scott.d.constable@...el.com,
 joao@...rdrivepizza.com,
 andrew.cooper3@...rix.com,
 jpoimboe@...nel.org,
 jose.marchesi@...cle.com,
 hjl.tools@...il.com,
 ndesaulniers@...gle.com,
 samitolvanen@...gle.com,
 nathan@...nel.org,
 ojeda@...nel.org,
 kees@...nel.org,
 alexei.starovoitov@...il.com,
 mhiramat@...nel.org,
 jmill@....edu
Subject: [PATCH v4 03/10] x86/traps: Decode 0xEA #UD

FineIBT will start using 0xEA as #UD

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/bug.h |    1 +
 arch/x86/kernel/traps.c    |   20 +++++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -25,6 +25,7 @@
 #define BUG_UD2			0xfffe
 #define BUG_UD1			0xfffd
 #define BUG_UD1_UBSAN		0xfffc
+#define BUG_EA			0xffea
 
 #ifdef CONFIG_GENERIC_BUG
 
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -96,6 +96,7 @@ __always_inline int is_valid_bugaddr(uns
  * Check for UD1 or UD2, accounting for Address Size Override Prefixes.
  * If it's a UD1, further decode to determine its use:
  *
+ * FineIBT:      ea                      (bad)
  * 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
@@ -113,6 +114,10 @@ __always_inline int decode_bug(unsigned
 	v = *(u8 *)(addr++);
 	if (v == INSN_ASOP)
 		v = *(u8 *)(addr++);
+	if (v == 0xea) {
+		*len = addr - start;
+		return BUG_EA;
+	}
 	if (v != OPCODE_ESCAPE)
 		return BUG_NONE;
 
@@ -309,10 +314,16 @@ static noinstr bool handle_bug(struct pt
 
 	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 += ud_len;
+		if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
+			handled = true;
+			break;
+		}
+		fallthrough;
+
+	case BUG_EA:
+		if (handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
 			handled = true;
+			break;
 		}
 		break;
 
@@ -328,6 +339,9 @@ static noinstr bool handle_bug(struct pt
 		break;
 	}
 
+	if (handled)
+		regs->ip += ud_len;
+
 	if (regs->flags & X86_EFLAGS_IF)
 		raw_local_irq_disable();
 	instrumentation_end();