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Subject[RESEND][PATCH v3 10/17] x86/static_call: Add inline static call implementation for x86-64
From: Josh Poimboeuf <jpoimboe@redhat.com>

Add the inline static call implementation for x86-64. The generated code
is identical to the out-of-line case, except we move the trampoline into
it's own section.

Then objtool uses the trampoline section to detect all the call sites,
which it writes into 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 | 25 ++++++
tools/objtool/check.c | 128 +++++++++++++++++++++++++++++++-
tools/objtool/check.h | 2
tools/objtool/elf.h | 1
tools/objtool/sync-check.sh | 1
10 files changed, 182 insertions(+), 3 deletions(-)
create mode 100644 tools/objtool/include/linux/static_call_types.h

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -210,6 +210,7 @@ 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
@@ -225,6 +226,7 @@ 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
@@ -450,7 +452,6 @@ 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
@@ -136,6 +136,7 @@ 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
@@ -609,6 +609,12 @@
*(.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 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _STATIC_CALL_TYPES_H
+#define _STATIC_CALL_TYPES_H
+
+#include <linux/types.h>
+#include <linux/stringify.h>
+
+#define STATIC_CALL_PREFIX __SC__
+#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

@@ -1345,6 +1346,21 @@ 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;
@@ -1416,6 +1432,10 @@ static int decode_sections(struct objtoo
if (ret)
return ret;

+ ret = read_static_call_tramps(file);
+ if (ret)
+ return ret;
+
return 0;
}

@@ -2143,6 +2163,12 @@ 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",
@@ -2463,6 +2489,98 @@ 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) {
+ INIT_LIST_HEAD(&file->static_call_list);
+ 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;
@@ -2488,12 +2606,13 @@ 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;
@@ -2532,6 +2651,11 @@ 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)
@@ -2540,7 +2664,9 @@ 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
@@ -7,6 +7,7 @@ arch/x86/include/asm/orc_types.h
arch/x86/include/asm/emulate_prefix.h
arch/x86/lib/x86-opcode-map.txt
arch/x86/tools/gen-insn-attr-x86.awk
+include/linux/static_call_types.h
'

check_2 () {

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