[PATCH v2 06/13] x86/static_call: Add inline static call implementation for x86-64

[Peter Zijlstra <peterz@infradead.org>]

From: Josh Poimboeuf <jpoimboe@redhat.com>

Add the inline static call implementation for x86-64.  For each key, a
temporary trampoline is created, named __static_call_tramp_<key>.  The
trampoline has an indirect jump to the destination function.

Objtool uses the trampoline naming convention to detect all the call
sites.  It then annotates those call sites in the .static_call_sites
section.

During boot (and module init), the call sites are patched to call
directly into the destination function.  The temporary trampoline is
then no longer used.

[peterz: merged trampolines, put trampoline in section]
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/Kconfig                        |    3 
 arch/x86/include/asm/static_call.h      |   15 +++
 arch/x86/kernel/static_call.c           |    3 
 arch/x86/kernel/vmlinux.lds.S           |    1 
 include/asm-generic/vmlinux.lds.h       |    6 +
 tools/include/linux/static_call_types.h |   24 ++++++
 tools/objtool/check.c                   |  127 +++++++++++++++++++++++++++++++-
 tools/objtool/check.h                   |    2 
 tools/objtool/elf.h                     |    1 
 tools/objtool/sync-check.sh             |    1 
 10 files changed, 180 insertions(+), 3 deletions(-)
 create mode 100644 tools/objtool/include/linux/static_call_types.h

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -206,6 +206,7 @@ config X86
 	select HAVE_STACKPROTECTOR		if CC_HAS_SANE_STACKPROTECTOR
 	select HAVE_STACK_VALIDATION		if X86_64
 	select HAVE_STATIC_CALL
+	select HAVE_STATIC_CALL_INLINE		if HAVE_STACK_VALIDATION
 	select HAVE_RSEQ
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UNSTABLE_SCHED_CLOCK
@@ -221,6 +222,7 @@ config X86
 	select RTC_MC146818_LIB
 	select SPARSE_IRQ
 	select SRCU
+	select STACK_VALIDATION			if HAVE_STACK_VALIDATION && (HAVE_STATIC_CALL_INLINE || RETPOLINE)
 	select SYSCTL_EXCEPTION_TRACE
 	select THREAD_INFO_IN_TASK
 	select USER_STACKTRACE_SUPPORT
@@ -445,7 +447,6 @@ config GOLDFISH
 config RETPOLINE
 	bool "Avoid speculative indirect branches in kernel"
 	default y
-	select STACK_VALIDATION if HAVE_STACK_VALIDATION
 	help
 	  Compile kernel with the retpoline compiler options to guard against
 	  kernel-to-user data leaks by avoiding speculative indirect
--- a/arch/x86/include/asm/static_call.h
+++ b/arch/x86/include/asm/static_call.h
@@ -5,12 +5,25 @@
 #include <asm/text-patching.h>
 
 /*
+ * For CONFIG_HAVE_STATIC_CALL_INLINE, this is a temporary trampoline which
+ * uses the current value of the key->func pointer to do an indirect jump to
+ * the function.  This trampoline is only used during boot, before the call
+ * sites get patched by static_call_update().  The name of this trampoline has
+ * a magical aspect: objtool uses it to find static call sites so it can create
+ * the .static_call_sites section.
+ *
  * For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
  * does a direct jump to the function.  The direct jump gets patched by
  * static_call_update().
+ *
+ * Having the trampoline in a special section has two benefits:
+ *  - it makes it 'easy' for objtool to find all the call-sites;
+ *  - it forces GCC to emit a JMP.d32 when it does tail-call optimization on
+ *    the call; since you cannot compute the relative displacement across
+ *    sections.
  */
 #define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func)			\
-	asm(".pushsection .text, \"ax\"				\n"	\
+	asm(".pushsection .static_call.text, \"ax\"		\n"	\
 	    ".align 4						\n"	\
 	    ".globl " STATIC_CALL_TRAMP_STR(name) "		\n"	\
 	    STATIC_CALL_TRAMP_STR(name) ":			\n"	\
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -26,6 +26,9 @@ void arch_static_call_transform(void *si
 	if (tramp)
 		__static_call_transform(tramp, JMP32_INSN_OPCODE, func);
 
+	if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site)
+		__static_call_transform(site, CALL_INSN_OPCODE, func);
+
 	mutex_unlock(&text_mutex);
 }
 EXPORT_SYMBOL_GPL(arch_static_call_transform);
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -133,6 +133,7 @@ SECTIONS
 		IRQENTRY_TEXT
 		ALIGN_ENTRY_TEXT_END
 		SOFTIRQENTRY_TEXT
+		STATIC_CALL_TEXT
 		*(.fixup)
 		*(.gnu.warning)
 
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -576,6 +576,12 @@
 		*(.softirqentry.text)					\
 		__softirqentry_text_end = .;
 
+#define STATIC_CALL_TEXT						\
+		ALIGN_FUNCTION();					\
+		__static_call_text_start = .;				\
+		*(.static_call.text)					\
+		__static_call_text_end = .;
+
 /* Section used for early init (in .S files) */
 #define HEAD_TEXT  KEEP(*(.head.text))
 
--- /dev/null
+++ b/tools/include/linux/static_call_types.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _STATIC_CALL_TYPES_H
+#define _STATIC_CALL_TYPES_H
+
+#include <linux/stringify.h>
+
+#define STATIC_CALL_PREFIX	____static_call_
+#define STATIC_CALL_PREFIX_STR	__stringify(STATIC_CALL_PREFIX)
+
+#define STATIC_CALL_NAME(name)	__PASTE(STATIC_CALL_PREFIX, name)
+
+#define STATIC_CALL_TRAMP(name)	    STATIC_CALL_NAME(name##_tramp)
+#define STATIC_CALL_TRAMP_STR(name) __stringify(STATIC_CALL_TRAMP(name))
+
+/*
+ * The static call site table needs to be created by external tooling (objtool
+ * or a compiler plugin).
+ */
+struct static_call_site {
+	s32 addr;
+	s32 key;
+};
+
+#endif /* _STATIC_CALL_TYPES_H */
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -15,6 +15,7 @@
 
 #include <linux/hashtable.h>
 #include <linux/kernel.h>
+#include <linux/static_call_types.h>
 
 #define FAKE_JUMP_OFFSET -1
 
@@ -1285,6 +1286,21 @@ static int read_retpoline_hints(struct o
 	return 0;
 }
 
+static int read_static_call_tramps(struct objtool_file *file)
+{
+	struct section *sec, *sc_sec = find_section_by_name(file->elf, ".static_call.text");
+	struct symbol *func;
+
+	for_each_sec(file, sec) {
+		list_for_each_entry(func, &sec->symbol_list, list) {
+			if (func->sec == sc_sec)
+				func->static_call_tramp = true;
+		}
+	}
+
+	return 0;
+}
+
 static void mark_rodata(struct objtool_file *file)
 {
 	struct section *sec;
@@ -1356,6 +1372,10 @@ static int decode_sections(struct objtoo
 	if (ret)
 		return ret;
 
+	ret = read_static_call_tramps(file);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
@@ -2083,6 +2103,12 @@ static int validate_branch(struct objtoo
 			if (ret)
 				return ret;
 
+			if (insn->type == INSN_CALL && insn->call_dest->static_call_tramp) {
+				list_add_tail(&insn->static_call_node,
+					      &file->static_call_list);
+			}
+
+
 			if (!no_fp && func && !is_fentry_call(insn) &&
 			    !has_valid_stack_frame(&state)) {
 				WARN_FUNC("call without frame pointer save/setup",
@@ -2403,6 +2429,97 @@ static int validate_reachable_instructio
 	return 0;
 }
 
+static int create_static_call_sections(struct objtool_file *file)
+{
+	struct section *sec, *rela_sec;
+	struct rela *rela;
+	struct static_call_site *site;
+	struct instruction *insn;
+	char *key_name, *tmp;
+	struct symbol *key_sym;
+	int idx;
+
+	sec = find_section_by_name(file->elf, ".static_call_sites");
+	if (sec) {
+		WARN("file already has .static_call_sites section, skipping");
+		return 0;
+	}
+
+	if (list_empty(&file->static_call_list))
+		return 0;
+
+	idx = 0;
+	list_for_each_entry(insn, &file->static_call_list, static_call_node)
+		idx++;
+
+	sec = elf_create_section(file->elf, ".static_call_sites",
+				 sizeof(struct static_call_site), idx);
+	if (!sec)
+		return -1;
+
+	rela_sec = elf_create_rela_section(file->elf, sec);
+	if (!rela_sec)
+		return -1;
+
+	idx = 0;
+	list_for_each_entry(insn, &file->static_call_list, static_call_node) {
+
+		site = (struct static_call_site *)sec->data->d_buf + idx;
+		memset(site, 0, sizeof(struct static_call_site));
+
+		/* populate rela for 'addr' */
+		rela = malloc(sizeof(*rela));
+		if (!rela) {
+			perror("malloc");
+			return -1;
+		}
+		memset(rela, 0, sizeof(*rela));
+		rela->sym = insn->sec->sym;
+		rela->addend = insn->offset;
+		rela->type = R_X86_64_PC32;
+		rela->offset = idx * sizeof(struct static_call_site);
+		list_add_tail(&rela->list, &rela_sec->rela_list);
+		hash_add(rela_sec->rela_hash, &rela->hash, rela->offset);
+
+		/* find key symbol */
+		key_name = strdup(insn->call_dest->name);
+		tmp = strstr(key_name, "_tramp");
+		if (!tmp) {
+			WARN("static_call: trampoline name malformed: %s", key_name);
+			return -1;
+		}
+		*tmp = 0;
+
+		key_sym = find_symbol_by_name(file->elf, key_name);
+		if (!key_sym) {
+			WARN("static_call: can't find static_call_key symbol: %s", key_name);
+			return -1;
+		}
+		free(key_name);
+
+		/* populate rela for 'key' */
+		rela = malloc(sizeof(*rela));
+		if (!rela) {
+			perror("malloc");
+			return -1;
+		}
+		memset(rela, 0, sizeof(*rela));
+		rela->sym = key_sym;
+		rela->addend = 0;
+		rela->type = R_X86_64_PC32;
+		rela->offset = idx * sizeof(struct static_call_site) + 4;
+		list_add_tail(&rela->list, &rela_sec->rela_list);
+		hash_add(rela_sec->rela_hash, &rela->hash, rela->offset);
+
+		idx++;
+	}
+
+	if (elf_rebuild_rela_section(rela_sec))
+		return -1;
+
+	return 0;
+}
+
 static void cleanup(struct objtool_file *file)
 {
 	struct instruction *insn, *tmpinsn;
@@ -2428,12 +2545,13 @@ int check(const char *_objname, bool orc
 
 	objname = _objname;
 
-	file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
+	file.elf = elf_read(objname, O_RDWR);
 	if (!file.elf)
 		return 1;
 
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
+	INIT_LIST_HEAD(&file.static_call_list);
 	file.c_file = find_section_by_name(file.elf, ".comment");
 	file.ignore_unreachables = no_unreachable;
 	file.hints = false;
@@ -2472,6 +2590,11 @@ int check(const char *_objname, bool orc
 		warnings += ret;
 	}
 
+	ret = create_static_call_sections(&file);
+	if (ret < 0)
+		goto out;
+	warnings += ret;
+
 	if (orc) {
 		ret = create_orc(&file);
 		if (ret < 0)
@@ -2480,7 +2603,9 @@ int check(const char *_objname, bool orc
 		ret = create_orc_sections(&file);
 		if (ret < 0)
 			goto out;
+	}
 
+	if (orc || !list_empty(&file.static_call_list)) {
 		ret = elf_write(file.elf);
 		if (ret < 0)
 			goto out;
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -28,6 +28,7 @@ struct insn_state {
 struct instruction {
 	struct list_head list;
 	struct hlist_node hash;
+	struct list_head static_call_node;
 	struct section *sec;
 	unsigned long offset;
 	unsigned int len;
@@ -51,6 +52,7 @@ struct objtool_file {
 	struct elf *elf;
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 16);
+	struct list_head static_call_list;
 	bool ignore_unreachables, c_file, hints, rodata;
 };
 
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -51,6 +51,7 @@ struct symbol {
 	unsigned int len;
 	struct symbol *pfunc, *cfunc, *alias;
 	bool uaccess_safe;
+	bool static_call_tramp;
 };
 
 struct rela {
--- a/tools/objtool/sync-check.sh
+++ b/tools/objtool/sync-check.sh
@@ -6,6 +6,7 @@ arch/x86/include/asm/inat_types.h
 arch/x86/include/asm/orc_types.h
 arch/x86/lib/x86-opcode-map.txt
 arch/x86/tools/gen-insn-attr-x86.awk
+include/linux/static_call_types.h
 '
 
 check_2 () {