Merge tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 retbleed fixes from Borislav Petkov:
 "Just when you thought that all the speculation bugs were addressed and
  solved and the nightmare is complete, here's the next one: speculating
  after RET instructions and leaking privileged information using the
  now pretty much classical covert channels.

  It is called RETBleed and the mitigation effort and controlling
  functionality has been modelled similar to what already existing
  mitigations provide"

* tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits)
  x86/speculation: Disable RRSBA behavior
  x86/kexec: Disable RET on kexec
  x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported
  x86/entry: Move PUSH_AND_CLEAR_REGS() back into error_entry
  x86/bugs: Add Cannon lake to RETBleed affected CPU list
  x86/retbleed: Add fine grained Kconfig knobs
  x86/cpu/amd: Enumerate BTC_NO
  x86/common: Stamp out the stepping madness
  KVM: VMX: Prevent RSB underflow before vmenter
  x86/speculation: Fill RSB on vmexit for IBRS
  KVM: VMX: Fix IBRS handling after vmexit
  KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS
  KVM: VMX: Convert launched argument to flags
  KVM: VMX: Flatten __vmx_vcpu_run()
  objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}
  x86/speculation: Remove x86_spec_ctrl_mask
  x86/speculation: Use cached host SPEC_CTRL value for guest entry/exit
  x86/speculation: Fix SPEC_CTRL write on SMT state change
  x86/speculation: Fix firmware entry SPEC_CTRL handling
  x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n
  ...

9 files changed, 356 insertions, 22 deletions

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 8b990a52aada..c260006106be 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -787,3 +787,8 @@ bool arch_is_retpoline(struct symbol *sym)
 {
 	return !strncmp(sym->name, "__x86_indirect_", 15);
 }
+
+bool arch_is_rethunk(struct symbol *sym)
+{
+	return !strcmp(sym->name, "__x86_return_thunk");
+}
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index f4c3a5091737..24fbe803a0d3 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -68,6 +68,8 @@ const struct option check_options[] = {
 	OPT_BOOLEAN('n', "noinstr", &opts.noinstr, "validate noinstr rules"),
 	OPT_BOOLEAN('o', "orc", &opts.orc, "generate ORC metadata"),
 	OPT_BOOLEAN('r', "retpoline", &opts.retpoline, "validate and annotate retpoline usage"),
+	OPT_BOOLEAN(0,   "rethunk", &opts.rethunk, "validate and annotate rethunk usage"),
+	OPT_BOOLEAN(0,   "unret", &opts.unret, "validate entry unret placement"),
 	OPT_BOOLEAN('l', "sls", &opts.sls, "validate straight-line-speculation mitigations"),
 	OPT_BOOLEAN('s', "stackval", &opts.stackval, "validate frame pointer rules"),
 	OPT_BOOLEAN('t', "static-call", &opts.static_call, "annotate static calls"),
@@ -123,6 +125,7 @@ static bool opts_valid(void)
 	    opts.noinstr		||
 	    opts.orc			||
 	    opts.retpoline		||
+	    opts.rethunk		||
 	    opts.sls			||
 	    opts.stackval		||
 	    opts.static_call		||
@@ -135,6 +138,11 @@ static bool opts_valid(void)
 		return true;
 	}
 
+	if (opts.unret && !opts.rethunk) {
+		ERROR("--unret requires --rethunk");
+		return false;
+	}
+
 	if (opts.dump_orc)
 		return true;
 
@@ -163,6 +171,11 @@ static bool link_opts_valid(struct objtool_file *file)
 		return false;
 	}
 
+	if (opts.unret) {
+		ERROR("--unret requires --link");
+		return false;
+	}
+
 	return true;
 }
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 57153e00349c..b341f8a8c7c5 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -376,7 +376,8 @@ static int decode_instructions(struct objtool_file *file)
 			sec->text = true;
 
 		if (!strcmp(sec->name, ".noinstr.text") ||
-		    !strcmp(sec->name, ".entry.text"))
+		    !strcmp(sec->name, ".entry.text") ||
+		    !strncmp(sec->name, ".text.__x86.", 12))
 			sec->noinstr = true;
 
 		for (offset = 0; offset < sec->sh.sh_size; offset += insn->len) {
@@ -749,6 +750,52 @@ static int create_retpoline_sites_sections(struct objtool_file *file)
 	return 0;
 }
 
+static int create_return_sites_sections(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct section *sec;
+	int idx;
+
+	sec = find_section_by_name(file->elf, ".return_sites");
+	if (sec) {
+		WARN("file already has .return_sites, skipping");
+		return 0;
+	}
+
+	idx = 0;
+	list_for_each_entry(insn, &file->return_thunk_list, call_node)
+		idx++;
+
+	if (!idx)
+		return 0;
+
+	sec = elf_create_section(file->elf, ".return_sites", 0,
+				 sizeof(int), idx);
+	if (!sec) {
+		WARN("elf_create_section: .return_sites");
+		return -1;
+	}
+
+	idx = 0;
+	list_for_each_entry(insn, &file->return_thunk_list, call_node) {
+
+		int *site = (int *)sec->data->d_buf + idx;
+		*site = 0;
+
+		if (elf_add_reloc_to_insn(file->elf, sec,
+					  idx * sizeof(int),
+					  R_X86_64_PC32,
+					  insn->sec, insn->offset)) {
+			WARN("elf_add_reloc_to_insn: .return_sites");
+			return -1;
+		}
+
+		idx++;
+	}
+
+	return 0;
+}
+
 static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 {
 	struct instruction *insn;
@@ -1083,6 +1130,11 @@ __weak bool arch_is_retpoline(struct symbol *sym)
 	return false;
 }
 
+__weak bool arch_is_rethunk(struct symbol *sym)
+{
+	return false;
+}
+
 #define NEGATIVE_RELOC	((void *)-1L)
 
 static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
@@ -1250,6 +1302,19 @@ static void add_retpoline_call(struct objtool_file *file, struct instruction *in
 	annotate_call_site(file, insn, false);
 }
 
+static void add_return_call(struct objtool_file *file, struct instruction *insn, bool add)
+{
+	/*
+	 * Return thunk tail calls are really just returns in disguise,
+	 * so convert them accordingly.
+	 */
+	insn->type = INSN_RETURN;
+	insn->retpoline_safe = true;
+
+	if (add)
+		list_add_tail(&insn->call_node, &file->return_thunk_list);
+}
+
 static bool same_function(struct instruction *insn1, struct instruction *insn2)
 {
 	return insn1->func->pfunc == insn2->func->pfunc;
@@ -1302,6 +1367,9 @@ static int add_jump_destinations(struct objtool_file *file)
 		} else if (reloc->sym->retpoline_thunk) {
 			add_retpoline_call(file, insn);
 			continue;
+		} else if (reloc->sym->return_thunk) {
+			add_return_call(file, insn, true);
+			continue;
 		} else if (insn->func) {
 			/*
 			 * External sibling call or internal sibling call with
@@ -1320,6 +1388,21 @@ static int add_jump_destinations(struct objtool_file *file)
 
 		jump_dest = find_insn(file, dest_sec, dest_off);
 		if (!jump_dest) {
+			struct symbol *sym = find_symbol_by_offset(dest_sec, dest_off);
+
+			/*
+			 * This is a special case for zen_untrain_ret().
+			 * It jumps to __x86_return_thunk(), but objtool
+			 * can't find the thunk's starting RET
+			 * instruction, because the RET is also in the
+			 * middle of another instruction.  Objtool only
+			 * knows about the outer instruction.
+			 */
+			if (sym && sym->return_thunk) {
+				add_return_call(file, insn, false);
+				continue;
+			}
+
 			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 				  insn->sec, insn->offset, dest_sec->name,
 				  dest_off);
@@ -1949,16 +2032,35 @@ static int read_unwind_hints(struct objtool_file *file)
 
 		insn->hint = true;
 
-		if (opts.ibt && hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
+		if (hint->type == UNWIND_HINT_TYPE_SAVE) {
+			insn->hint = false;
+			insn->save = true;
+			continue;
+		}
+
+		if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
+			insn->restore = true;
+			continue;
+		}
+
+		if (hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
 			struct symbol *sym = find_symbol_by_offset(insn->sec, insn->offset);
 
-			if (sym && sym->bind == STB_GLOBAL &&
-			    insn->type != INSN_ENDBR && !insn->noendbr) {
-				WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
-					  insn->sec, insn->offset);
+			if (sym && sym->bind == STB_GLOBAL) {
+				if (opts.ibt && insn->type != INSN_ENDBR && !insn->noendbr) {
+					WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
+						  insn->sec, insn->offset);
+				}
+
+				insn->entry = 1;
 			}
 		}
 
+		if (hint->type == UNWIND_HINT_TYPE_ENTRY) {
+			hint->type = UNWIND_HINT_TYPE_CALL;
+			insn->entry = 1;
+		}
+
 		if (hint->type == UNWIND_HINT_TYPE_FUNC) {
 			insn->cfi = &func_cfi;
 			continue;
@@ -2032,8 +2134,10 @@ static int read_retpoline_hints(struct objtool_file *file)
 		}
 
 		if (insn->type != INSN_JUMP_DYNAMIC &&
-		    insn->type != INSN_CALL_DYNAMIC) {
-			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
+		    insn->type != INSN_CALL_DYNAMIC &&
+		    insn->type != INSN_RETURN &&
+		    insn->type != INSN_NOP) {
+			WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret/nop",
 				  insn->sec, insn->offset);
 			return -1;
 		}
@@ -2184,6 +2288,9 @@ static int classify_symbols(struct objtool_file *file)
 			if (arch_is_retpoline(func))
 				func->retpoline_thunk = true;
 
+			if (arch_is_rethunk(func))
+				func->return_thunk = true;
+
 			if (!strcmp(func->name, "__fentry__"))
 				func->fentry = true;
 
@@ -3218,8 +3325,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			return 1;
 		}
 
-		visited = 1 << state.uaccess;
-		if (insn->visited) {
+		visited = VISITED_BRANCH << state.uaccess;
+		if (insn->visited & VISITED_BRANCH_MASK) {
 			if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
 				return 1;
 
@@ -3233,6 +3340,35 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			state.instr += insn->instr;
 
 		if (insn->hint) {
+			if (insn->restore) {
+				struct instruction *save_insn, *i;
+
+				i = insn;
+				save_insn = NULL;
+
+				sym_for_each_insn_continue_reverse(file, func, i) {
+					if (i->save) {
+						save_insn = i;
+						break;
+					}
+				}
+
+				if (!save_insn) {
+					WARN_FUNC("no corresponding CFI save for CFI restore",
+						  sec, insn->offset);
+					return 1;
+				}
+
+				if (!save_insn->visited) {
+					WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
+						  sec, insn->offset);
+					return 1;
+				}
+
+				insn->cfi = save_insn->cfi;
+				nr_cfi_reused++;
+			}
+
 			state.cfi = *insn->cfi;
 		} else {
 			/* XXX track if we actually changed state.cfi */
@@ -3433,6 +3569,145 @@ static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
 	return warnings;
 }
 
+/*
+ * Validate rethunk entry constraint: must untrain RET before the first RET.
+ *
+ * Follow every branch (intra-function) and ensure ANNOTATE_UNRET_END comes
+ * before an actual RET instruction.
+ */
+static int validate_entry(struct objtool_file *file, struct instruction *insn)
+{
+	struct instruction *next, *dest;
+	int ret, warnings = 0;
+
+	for (;;) {
+		next = next_insn_to_validate(file, insn);
+
+		if (insn->visited & VISITED_ENTRY)
+			return 0;
+
+		insn->visited |= VISITED_ENTRY;
+
+		if (!insn->ignore_alts && !list_empty(&insn->alts)) {
+			struct alternative *alt;
+			bool skip_orig = false;
+
+			list_for_each_entry(alt, &insn->alts, list) {
+				if (alt->skip_orig)
+					skip_orig = true;
+
+				ret = validate_entry(file, alt->insn);
+				if (ret) {
+				        if (opts.backtrace)
+						BT_FUNC("(alt)", insn);
+					return ret;
+				}
+			}
+
+			if (skip_orig)
+				return 0;
+		}
+
+		switch (insn->type) {
+
+		case INSN_CALL_DYNAMIC:
+		case INSN_JUMP_DYNAMIC:
+		case INSN_JUMP_DYNAMIC_CONDITIONAL:
+			WARN_FUNC("early indirect call", insn->sec, insn->offset);
+			return 1;
+
+		case INSN_JUMP_UNCONDITIONAL:
+		case INSN_JUMP_CONDITIONAL:
+			if (!is_sibling_call(insn)) {
+				if (!insn->jump_dest) {
+					WARN_FUNC("unresolved jump target after linking?!?",
+						  insn->sec, insn->offset);
+					return -1;
+				}
+				ret = validate_entry(file, insn->jump_dest);
+				if (ret) {
+					if (opts.backtrace) {
+						BT_FUNC("(branch%s)", insn,
+							insn->type == INSN_JUMP_CONDITIONAL ? "-cond" : "");
+					}
+					return ret;
+				}
+
+				if (insn->type == INSN_JUMP_UNCONDITIONAL)
+					return 0;
+
+				break;
+			}
+
+			/* fallthrough */
+		case INSN_CALL:
+			dest = find_insn(file, insn->call_dest->sec,
+					 insn->call_dest->offset);
+			if (!dest) {
+				WARN("Unresolved function after linking!?: %s",
+				     insn->call_dest->name);
+				return -1;
+			}
+
+			ret = validate_entry(file, dest);
+			if (ret) {
+				if (opts.backtrace)
+					BT_FUNC("(call)", insn);
+				return ret;
+			}
+			/*
+			 * If a call returns without error, it must have seen UNTRAIN_RET.
+			 * Therefore any non-error return is a success.
+			 */
+			return 0;
+
+		case INSN_RETURN:
+			WARN_FUNC("RET before UNTRAIN", insn->sec, insn->offset);
+			return 1;
+
+		case INSN_NOP:
+			if (insn->retpoline_safe)
+				return 0;
+			break;
+
+		default:
+			break;
+		}
+
+		if (!next) {
+			WARN_FUNC("teh end!", insn->sec, insn->offset);
+			return -1;
+		}
+		insn = next;
+	}
+
+	return warnings;
+}
+
+/*
+ * Validate that all branches starting at 'insn->entry' encounter UNRET_END
+ * before RET.
+ */
+static int validate_unret(struct objtool_file *file)
+{
+	struct instruction *insn;
+	int ret, warnings = 0;
+
+	for_each_insn(file, insn) {
+		if (!insn->entry)
+			continue;
+
+		ret = validate_entry(file, insn);
+		if (ret < 0) {
+			WARN_FUNC("Failed UNRET validation", insn->sec, insn->offset);
+			return ret;
+		}
+		warnings += ret;
+	}
+
+	return warnings;
+}
+
 static int validate_retpoline(struct objtool_file *file)
 {
 	struct instruction *insn;
@@ -3440,7 +3715,8 @@ static int validate_retpoline(struct objtool_file *file)
 
 	for_each_insn(file, insn) {
 		if (insn->type != INSN_JUMP_DYNAMIC &&
-		    insn->type != INSN_CALL_DYNAMIC)
+		    insn->type != INSN_CALL_DYNAMIC &&
+		    insn->type != INSN_RETURN)
 			continue;
 
 		if (insn->retpoline_safe)
@@ -3455,9 +3731,17 @@ static int validate_retpoline(struct objtool_file *file)
 		if (!strcmp(insn->sec->name, ".init.text") && !opts.module)
 			continue;
 
-		WARN_FUNC("indirect %s found in RETPOLINE build",
-			  insn->sec, insn->offset,
-			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+		if (insn->type == INSN_RETURN) {
+			if (opts.rethunk) {
+				WARN_FUNC("'naked' return found in RETHUNK build",
+					  insn->sec, insn->offset);
+			} else
+				continue;
+		} else {
+			WARN_FUNC("indirect %s found in RETPOLINE build",
+				  insn->sec, insn->offset,
+				  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+		}
 
 		warnings++;
 	}
@@ -3945,6 +4229,17 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}
 
+	if (opts.unret) {
+		/*
+		 * Must be after validate_branch() and friends, it plays
+		 * further games with insn->visited.
+		 */
+		ret = validate_unret(file);
+		if (ret < 0)
+			return ret;
+		warnings += ret;
+	}
+
 	if (opts.ibt) {
 		ret = validate_ibt(file);
 		if (ret < 0)
@@ -3973,6 +4268,13 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}
 
+	if (opts.rethunk) {
+		ret = create_return_sites_sections(file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
+	}
+
 	if (opts.mcount) {
 		ret = create_mcount_loc_sections(file);
 		if (ret < 0)
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 9b19cc304195..beb2f3aa94ff 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -89,6 +89,7 @@ const char *arch_ret_insn(int len);
 int arch_decode_hint_reg(u8 sp_reg, int *base);
 
 bool arch_is_retpoline(struct symbol *sym);
+bool arch_is_rethunk(struct symbol *sym);
 
 int arch_rewrite_retpolines(struct objtool_file *file);
 
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 280ea18b7f2b..42a52f1a0add 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -19,6 +19,8 @@ struct opts {
 	bool noinstr;
 	bool orc;
 	bool retpoline;
+	bool rethunk;
+	bool unret;
 	bool sls;
 	bool stackval;
 	bool static_call;
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index f10d7374f388..036129cebeee 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -46,16 +46,19 @@ struct instruction {
 	enum insn_type type;
 	unsigned long immediate;
 
-	u8 dead_end	: 1,
-	   ignore	: 1,
-	   ignore_alts	: 1,
-	   hint		: 1,
-	   retpoline_safe : 1,
-	   noendbr	: 1;
-		/* 2 bit hole */
+	u16 dead_end		: 1,
+	   ignore		: 1,
+	   ignore_alts		: 1,
+	   hint			: 1,
+	   save			: 1,
+	   restore		: 1,
+	   retpoline_safe	: 1,
+	   noendbr		: 1,
+	   entry		: 1;
+		/* 7 bit hole */
+
 	s8 instr;
 	u8 visited;
-	/* u8 hole */
 
 	struct alt_group *alt_group;
 	struct symbol *call_dest;
@@ -69,6 +72,11 @@ struct instruction {
 	struct cfi_state *cfi;
 };
 
+#define VISITED_BRANCH		0x01
+#define VISITED_BRANCH_UACCESS	0x02
+#define VISITED_BRANCH_MASK	0x03
+#define VISITED_ENTRY		0x04
+
 static inline bool is_static_jump(struct instruction *insn)
 {
 	return insn->type == INSN_JUMP_CONDITIONAL ||
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index adebfbc2b518..16f4067b82ae 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -57,6 +57,7 @@ struct symbol {
 	u8 uaccess_safe      : 1;
 	u8 static_call_tramp : 1;
 	u8 retpoline_thunk   : 1;
+	u8 return_thunk      : 1;
 	u8 fentry            : 1;
 	u8 profiling_func    : 1;
 	struct list_head pv_target;
diff --git a/tools/objtool/include/objtool/objtool.h b/tools/objtool/include/objtool/objtool.h
index a6e72d916807..7f2d1b095333 100644
--- a/tools/objtool/include/objtool/objtool.h
+++ b/tools/objtool/include/objtool/objtool.h
@@ -24,6 +24,7 @@ struct objtool_file {
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 20);
 	struct list_head retpoline_call_list;
+	struct list_head return_thunk_list;
 	struct list_head static_call_list;
 	struct list_head mcount_loc_list;
 	struct list_head endbr_list;
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index 512669ce064c..a7ecc32e3512 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -102,6 +102,7 @@ struct objtool_file *objtool_open_read(const char *_objname)
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
 	INIT_LIST_HEAD(&file.retpoline_call_list);
+	INIT_LIST_HEAD(&file.return_thunk_list);
 	INIT_LIST_HEAD(&file.static_call_list);
 	INIT_LIST_HEAD(&file.mcount_loc_list);
 	INIT_LIST_HEAD(&file.endbr_list);