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Date: Tue, 7 May 2024 07:38:32 -0700
From: "Paul E. McKenney" <paulmck@kernel.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: x86@kernel.org, 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>
Subject: Re: [PATCH v5 1/3] x86/syscall: Mark exit[_group] syscall handlers
 __noreturn
Message-ID: <31af8226-8357-493e-a280-465f91b58d35@paulmck-laptop>
Reply-To: paulmck@kernel.org
References: <cover.1715059256.git.jpoimboe@kernel.org>
 <9ad251f6258adde596fb1f4d6826309b9f239ed3.1715059256.git.jpoimboe@kernel.org>
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In-Reply-To: <9ad251f6258adde596fb1f4d6826309b9f239ed3.1715059256.git.jpoimboe@kernel.org>

On Mon, May 06, 2024 at 10:30:04PM -0700, Josh Poimboeuf wrote:
> 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>

Just reaffirming my Tested-by, and thank you!

							Thanx, Paul

> 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
>