Merge tag 'objtool-urgent-2025-04-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull misc objtool fixes from Ingo Molnar:

 - Remove the recently introduced ANNOTATE_IGNORE_ALTERNATIVE noise from
   clac()/stac() code to make .s files more readable

 - Fix INSN_SYSCALL / INSN_SYSRET semantics

 - Fix various false-positive warnings

* tag 'objtool-urgent-2025-04-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  objtool: Fix false-positive "ignoring unreachables" warning
  objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC
  objtool, xen: Fix INSN_SYSCALL / INSN_SYSRET semantics
  objtool: Stop UNRET validation on UD2
  objtool: Split INSN_CONTEXT_SWITCH into INSN_SYSCALL and INSN_SYSRET
  objtool: Fix INSN_CONTEXT_SWITCH handling in validate_unret()

4 files changed, 65 insertions, 17 deletions

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 33d861c04ebd..3ce7b54003c2 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -522,7 +522,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 			case INAT_PFX_REPNE:
 				if (modrm == 0xca)
 					/* eretu/erets */
-					insn->type = INSN_CONTEXT_SWITCH;
+					insn->type = INSN_SYSRET;
 				break;
 			default:
 				if (modrm == 0xca)
@@ -535,11 +535,15 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 
 			insn->type = INSN_JUMP_CONDITIONAL;
 
-		} else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
-			   op2 == 0x35) {
+		} else if (op2 == 0x05 || op2 == 0x34) {
 
-			/* sysenter, sysret */
-			insn->type = INSN_CONTEXT_SWITCH;
+			/* syscall, sysenter */
+			insn->type = INSN_SYSCALL;
+
+		} else if (op2 == 0x07 || op2 == 0x35) {
+
+			/* sysret, sysexit */
+			insn->type = INSN_SYSRET;
 
 		} else if (op2 == 0x0b || op2 == 0xb9) {
 
@@ -676,7 +680,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 
 	case 0xca: /* retf */
 	case 0xcb: /* retf */
-		insn->type = INSN_CONTEXT_SWITCH;
+		insn->type = INSN_SYSRET;
 		break;
 
 	case 0xe0: /* loopne */
@@ -721,7 +725,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 		} else if (modrm_reg == 5) {
 
 			/* jmpf */
-			insn->type = INSN_CONTEXT_SWITCH;
+			insn->type = INSN_SYSRET;
 
 		} else if (modrm_reg == 6) {
 
diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
index 403e587676f1..06ca4a2659a4 100644
--- a/tools/objtool/arch/x86/special.c
+++ b/tools/objtool/arch/x86/special.c
@@ -126,7 +126,7 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
 	 * indicates a rare GCC quirk/bug which can leave dead
 	 * code behind.
 	 */
-	if (reloc_type(text_reloc) == R_X86_64_PC32) {
+	if (!file->ignore_unreachables && reloc_type(text_reloc) == R_X86_64_PC32) {
 		WARN_INSN(insn, "ignoring unreachables due to jump table quirk");
 		file->ignore_unreachables = true;
 	}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4a1f6c3169b3..b649049b6a11 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3505,6 +3505,34 @@ next_orig:
 	return next_insn_same_sec(file, alt_group->orig_group->last_insn);
 }
 
+static bool skip_alt_group(struct instruction *insn)
+{
+	struct instruction *alt_insn = insn->alts ? insn->alts->insn : NULL;
+
+	/* ANNOTATE_IGNORE_ALTERNATIVE */
+	if (insn->alt_group && insn->alt_group->ignore)
+		return true;
+
+	/*
+	 * For NOP patched with CLAC/STAC, only follow the latter to avoid
+	 * impossible code paths combining patched CLAC with unpatched STAC
+	 * or vice versa.
+	 *
+	 * ANNOTATE_IGNORE_ALTERNATIVE could have been used here, but Linus
+	 * requested not to do that to avoid hurting .s file readability
+	 * around CLAC/STAC alternative sites.
+	 */
+
+	if (!alt_insn)
+		return false;
+
+	/* Don't override ASM_{CLAC,STAC}_UNSAFE */
+	if (alt_insn->alt_group && alt_insn->alt_group->ignore)
+		return false;
+
+	return alt_insn->type == INSN_CLAC || alt_insn->type == INSN_STAC;
+}
+
 /*
  * Follow the branch starting at the given instruction, and recursively follow
  * any other branches (jumps).  Meanwhile, track the frame pointer state at
@@ -3625,7 +3653,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			}
 		}
 
-		if (insn->alt_group && insn->alt_group->ignore)
+		if (skip_alt_group(insn))
 			return 0;
 
 		if (handle_insn_ops(insn, next_insn, &state))
@@ -3684,14 +3712,20 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 			break;
 
-		case INSN_CONTEXT_SWITCH:
-			if (func) {
-				if (!next_insn || !next_insn->hint) {
-					WARN_INSN(insn, "unsupported instruction in callable function");
-					return 1;
-				}
-				break;
+		case INSN_SYSCALL:
+			if (func && (!next_insn || !next_insn->hint)) {
+				WARN_INSN(insn, "unsupported instruction in callable function");
+				return 1;
+			}
+
+			break;
+
+		case INSN_SYSRET:
+			if (func && (!next_insn || !next_insn->hint)) {
+				WARN_INSN(insn, "unsupported instruction in callable function");
+				return 1;
 			}
+
 			return 0;
 
 		case INSN_STAC:
@@ -3886,6 +3920,12 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
 			WARN_INSN(insn, "RET before UNTRAIN");
 			return 1;
 
+		case INSN_SYSCALL:
+			break;
+
+		case INSN_SYSRET:
+			return 0;
+
 		case INSN_NOP:
 			if (insn->retpoline_safe)
 				return 0;
@@ -3895,6 +3935,9 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
 			break;
 		}
 
+		if (insn->dead_end)
+			return 0;
+
 		if (!next) {
 			WARN_INSN(insn, "teh end!");
 			return 1;
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 089a1acc48a8..01ef6f415adf 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -19,7 +19,8 @@ enum insn_type {
 	INSN_CALL,
 	INSN_CALL_DYNAMIC,
 	INSN_RETURN,
-	INSN_CONTEXT_SWITCH,
+	INSN_SYSCALL,
+	INSN_SYSRET,
 	INSN_BUG,
 	INSN_NOP,
 	INSN_STAC,