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From: Josh Poimboeuf <jpoimboe@kernel.org>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@linux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Nikolay Borisov <nik.borisov@suse.com>,
	KP Singh <kpsingh@kernel.org>,
	Waiman Long <longman@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Ingo Molnar <mingo@kernel.org>,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH v5 1/3] x86/syscall: Mark exit[_group] syscall handlers __noreturn
Date: Mon,  6 May 2024 22:30:04 -0700
Message-ID: <9ad251f6258adde596fb1f4d6826309b9f239ed3.1715059256.git.jpoimboe@kernel.org>
In-Reply-To: <cover.1715059256.git.jpoimboe@kernel.org>
References: <cover.1715059256.git.jpoimboe@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

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 those 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: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/entry/syscall_32.c            | 10 ++++++----
 arch/x86/entry/syscall_64.c            |  9 ++++++---
 arch/x86/entry/syscall_x32.c           |  7 +++++--
 arch/x86/entry/syscalls/syscall_32.tbl |  6 +++---
 arch/x86/entry/syscalls/syscall_64.tbl |  6 +++---
 arch/x86/um/sys_call_table_32.c        | 10 ++++++----
 arch/x86/um/sys_call_table_64.c        | 11 +++++++----
 scripts/syscalltbl.sh                  | 18 ++++++++++++++++--
 tools/objtool/noreturns.h              |  4 ++++
 9 files changed, 56 insertions(+), 25 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
+
+#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 5f8591ce7f25..9e9a908cd50d 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 7e8d46f4147f..5ea7387c1aa1 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
diff --git a/arch/x86/um/sys_call_table_32.c b/arch/x86/um/sys_call_table_32.c
index 89df5d89d664..51655133eee3 100644
--- a/arch/x86/um/sys_call_table_32.c
+++ b/arch/x86/um/sys_call_table_32.c
@@ -9,6 +9,10 @@
 #include <linux/cache.h>
 #include <asm/syscall.h>
 
+extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
+				      unsigned long, unsigned long,
+				      unsigned long, unsigned long);
+
 /*
  * Below you can see, in terms of #define's, the differences between the x86-64
  * and the UML syscall table.
@@ -22,15 +26,13 @@
 #define sys_vm86 sys_ni_syscall
 
 #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, native)
+#define __SYSCALL_NORETURN __SYSCALL
 
 #define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
 #include <asm/syscalls_32.h>
+#undef  __SYSCALL
 
-#undef __SYSCALL
 #define __SYSCALL(nr, sym) sym,
-
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
-
 const sys_call_ptr_t sys_call_table[] ____cacheline_aligned = {
 #include <asm/syscalls_32.h>
 };
diff --git a/arch/x86/um/sys_call_table_64.c b/arch/x86/um/sys_call_table_64.c
index b0b4cfd2308c..943d414f2109 100644
--- a/arch/x86/um/sys_call_table_64.c
+++ b/arch/x86/um/sys_call_table_64.c
@@ -9,6 +9,10 @@
 #include <linux/cache.h>
 #include <asm/syscall.h>
 
+extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
+				      unsigned long, unsigned long,
+				      unsigned long, unsigned long);
+
 /*
  * Below you can see, in terms of #define's, the differences between the x86-64
  * and the UML syscall table.
@@ -18,14 +22,13 @@
 #define sys_iopl sys_ni_syscall
 #define sys_ioperm sys_ni_syscall
 
+#define __SYSCALL_NORETURN __SYSCALL
+
 #define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
 #include <asm/syscalls_64.h>
+#undef  __SYSCALL
 
-#undef __SYSCALL
 #define __SYSCALL(nr, sym) sym,
-
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
-
 const sys_call_ptr_t sys_call_table[] ____cacheline_aligned = {
 #include <asm/syscalls_64.h>
 };
diff --git a/scripts/syscalltbl.sh b/scripts/syscalltbl.sh
index 6abe143889ef..6a903b87a7c2 100755
--- a/scripts/syscalltbl.sh
+++ b/scripts/syscalltbl.sh
@@ -54,7 +54,7 @@ nxt=0
 
 grep -E "^[0-9]+[[:space:]]+$abis" "$infile" | {
 
-	while read nr abi name native compat ; do
+	while read nr abi name native compat noreturn; do
 
 		if [ $nxt -gt $nr ]; then
 			echo "error: $infile: syscall table is not sorted or duplicates the same syscall number" >&2
@@ -66,7 +66,21 @@ grep -E "^[0-9]+[[:space:]]+$abis" "$infile" | {
 			nxt=$((nxt + 1))
 		done
 
-		if [ -n "$compat" ]; then
+		if [ "$compat" = "-" ]; then
+			unset compat
+		fi
+
+		if [ -n "$noreturn" ]; then
+			if [ "$noreturn" != "noreturn" ]; then
+				echo "error: $infile: invalid string \"$noreturn\" in 'noreturn' column"
+				exit 1
+			fi
+			if [ -n "$compat" ]; then
+				echo "__SYSCALL_COMPAT_NORETURN($nr, $native, $compat)"
+			else
+				echo "__SYSCALL_NORETURN($nr, $native)"
+			fi
+		elif [ -n "$compat" ]; then
 			echo "__SYSCALL_WITH_COMPAT($nr, $native, $compat)"
 		elif [ -n "$native" ]; then
 			echo "__SYSCALL($nr, $native)"
diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
index 7ebf29c91184..1e8141ef1b15 100644
--- a/tools/objtool/noreturns.h
+++ b/tools/objtool/noreturns.h
@@ -7,12 +7,16 @@
  * Yes, this is unfortunate.  A better solution is in the works.
  */
 NORETURN(__fortify_panic)
+NORETURN(__ia32_sys_exit)
+NORETURN(__ia32_sys_exit_group)
 NORETURN(__kunit_abort)
 NORETURN(__module_put_and_kthread_exit)
 NORETURN(__reiserfs_panic)
 NORETURN(__stack_chk_fail)
 NORETURN(__tdx_hypercall_failed)
 NORETURN(__ubsan_handle_builtin_unreachable)
+NORETURN(__x64_sys_exit)
+NORETURN(__x64_sys_exit_group)
 NORETURN(arch_cpu_idle_dead)
 NORETURN(bch2_trans_in_restart_error)
 NORETURN(bch2_trans_restart_error)
-- 
2.44.0