x86/syscall: Mark exit[_group] syscall handlers __noreturn

The direct-call syscall dispatch function doesn't know that the exit()
and exit_group() syscall handlers don't return, so the call sites aren't
optimized accordingly.

Fix that by marking the exit syscall declarations __noreturn.

Fixes the following warnings:

  vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
  vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation

Fixes: 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/5d8882bc077d8eadcc7fd1740b56dfb781f12288.1719381528.git.jpoimboe@kernel.org

5 files changed, 23 insertions, 15 deletions

diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
index c2235bae17ef..8cc9950d7104 100644
--- a/arch/x86/entry/syscall_32.c
+++ b/arch/x86/entry/syscall_32.c
@@ -14,9 +14,12 @@
 #endif
 
 #define __SYSCALL(nr, sym) extern long __ia32_##sym(const struct pt_regs *);
-
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __ia32_##sym(const struct pt_regs *);
 #include <asm/syscalls_32.h>
-#undef __SYSCALL
+#undef  __SYSCALL
+
+#undef  __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
 
 /*
  * The sys_call_table[] is no longer used for system calls, but
@@ -28,11 +31,10 @@
 const sys_call_ptr_t sys_call_table[] = {
 #include <asm/syscalls_32.h>
 };
-#undef __SYSCALL
+#undef  __SYSCALL
 #endif
 
 #define __SYSCALL(nr, sym) case nr: return __ia32_##sym(regs);
-
 long ia32_sys_call(const struct pt_regs *regs, unsigned int nr)
 {
 	switch (nr) {
diff --git a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
index 33b3f09e6f15..ba8354424860 100644
--- a/arch/x86/entry/syscall_64.c
+++ b/arch/x86/entry/syscall_64.c
@@ -8,8 +8,12 @@
 #include <asm/syscall.h>
 
 #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
 #include <asm/syscalls_64.h>
-#undef __SYSCALL
+#undef  __SYSCALL
+
+#undef  __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
 
 /*
  * The sys_call_table[] is no longer used for system calls, but
@@ -20,10 +24,9 @@
 const sys_call_ptr_t sys_call_table[] = {
 #include <asm/syscalls_64.h>
 };
-#undef __SYSCALL
+#undef  __SYSCALL
 
 #define __SYSCALL(nr, sym) case nr: return __x64_##sym(regs);
-
 long x64_sys_call(const struct pt_regs *regs, unsigned int nr)
 {
 	switch (nr) {
diff --git a/arch/x86/entry/syscall_x32.c b/arch/x86/entry/syscall_x32.c
index 03de4a932131..fb77908f44f3 100644
--- a/arch/x86/entry/syscall_x32.c
+++ b/arch/x86/entry/syscall_x32.c
@@ -8,11 +8,14 @@
 #include <asm/syscall.h>
 
 #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
 #include <asm/syscalls_x32.h>
-#undef __SYSCALL
+#undef  __SYSCALL
 
-#define __SYSCALL(nr, sym) case nr: return __x64_##sym(regs);
+#undef  __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
 
+#define __SYSCALL(nr, sym) case nr: return __x64_##sym(regs);
 long x32_sys_call(const struct pt_regs *regs, unsigned int nr)
 {
 	switch (nr) {
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 7fd1f57ad3d3..09ca75bb51a0 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -2,7 +2,7 @@
 # 32-bit system call numbers and entry vectors
 #
 # The format is:
-# <number> <abi> <name> <entry point> <compat entry point>
+# <number> <abi> <name> <entry point> [<compat entry point> [noreturn]]
 #
 # The __ia32_sys and __ia32_compat_sys stubs are created on-the-fly for
 # sys_*() system calls and compat_sys_*() compat system calls if
@@ -12,7 +12,7 @@
 # The abi is always "i386" for this file.
 #
 0	i386	restart_syscall		sys_restart_syscall
-1	i386	exit			sys_exit
+1	i386	exit			sys_exit			-			noreturn
 2	i386	fork			sys_fork
 3	i386	read			sys_read
 4	i386	write			sys_write
@@ -263,7 +263,7 @@
 249	i386	io_cancel		sys_io_cancel
 250	i386	fadvise64		sys_ia32_fadvise64
 # 251 is available for reuse (was briefly sys_set_zone_reclaim)
-252	i386	exit_group		sys_exit_group
+252	i386	exit_group		sys_exit_group			-			noreturn
 253	i386	lookup_dcookie
 254	i386	epoll_create		sys_epoll_create
 255	i386	epoll_ctl		sys_epoll_ctl
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index a396f6e6ab5b..a8068f937290 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -2,7 +2,7 @@
 # 64-bit system call numbers and entry vectors
 #
 # The format is:
-# <number> <abi> <name> <entry point>
+# <number> <abi> <name> <entry point> [<compat entry point> [noreturn]]
 #
 # The __x64_sys_*() stubs are created on-the-fly for sys_*() system calls
 #
@@ -68,7 +68,7 @@
 57	common	fork			sys_fork
 58	common	vfork			sys_vfork
 59	64	execve			sys_execve
-60	common	exit			sys_exit
+60	common	exit			sys_exit			-			noreturn
 61	common	wait4			sys_wait4
 62	common	kill			sys_kill
 63	common	uname			sys_newuname
@@ -239,7 +239,7 @@
 228	common	clock_gettime		sys_clock_gettime
 229	common	clock_getres		sys_clock_getres
 230	common	clock_nanosleep		sys_clock_nanosleep
-231	common	exit_group		sys_exit_group
+231	common	exit_group		sys_exit_group			-			noreturn
 232	common	epoll_wait		sys_epoll_wait
 233	common	epoll_ctl		sys_epoll_ctl
 234	common	tgkill			sys_tgkill