linux-kernel - Re: [PATCH v3 2/2] arch: wire-up clone3() syscall

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Date:   Fri, 21 Jun 2019 00:10:04 +0200
From:   Christian Brauner <christian@...uner.io>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, jannh@...gle.com,
        keescook@...omium.org, fweimer@...hat.com, oleg@...hat.com,
        arnd@...db.de, dhowells@...hat.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Adrian Reber <adrian@...as.de>, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 2/2] arch: wire-up clone3() syscall

On Thu, Jun 20, 2019 at 11:44:51AM -0700, Guenter Roeck wrote:
> On Tue, Jun 04, 2019 at 06:09:44PM +0200, Christian Brauner wrote:
> > Wire up the clone3() call on all arches that don't require hand-rolled
> > assembly.
> > 
> > Some of the arches look like they need special assembly massaging and it is
> > probably smarter if the appropriate arch maintainers would do the actual
> > wiring. Arches that are wired-up are:
> > - x86{_32,64}
> > - arm{64}
> > - xtensa
> > 
> 
> This patch results in build failures on various architecetures.
> 
> h8300-linux-ld: arch/h8300/kernel/syscalls.o:(.data+0x6d0): undefined reference to `sys_clone3'
> 
> nios2-linux-ld: arch/nios2/kernel/syscall_table.o:(.data+0x6d0): undefined reference to `sys_clone3'
> 
> There may be others; -next is in too bad shape right now to get a complete
> picture. Wondering, though: What is special with this syscall ? Normally
> one would only get a warning that a syscall is not wired up.

clone3() was placed under __ARCH_WANT_SYS_CLONE. Most architectures
simply define __ARCH_WANT_SYS_CLONE and are done with it.
Some however, such as nios2 and h8300 don't define it but instead
provide a sys_clone stub of their own because of architectural
requirements (or tweaks) and they are mostly written in assembly. (That
should be left to arch maintainers for sys_clone3.)

The build failures were on my radar already. I hadn't yet replied
since I haven't pushed the fixup below.
The solution is to define __ARCH_WANT_SYS_CLONE3 and add a
cond_syscall(clone3) so we catch all architectures that do not yet
provide clone3 with a ENOSYS until maintainers have added it.

diff --git a/arch/arm/include/asm/unistd.h b/arch/arm/include/asm/unistd.h
index 7a39e77984ef..aa35aa5d68dc 100644
--- a/arch/arm/include/asm/unistd.h
+++ b/arch/arm/include/asm/unistd.h
@@ -40,6 +40,7 @@
 #define __ARCH_WANT_SYS_FORK
 #define __ARCH_WANT_SYS_VFORK
 #define __ARCH_WANT_SYS_CLONE
+#define __ARCH_WANT_SYS_CLONE3
 
 /*
  * Unimplemented (or alternatively implemented) syscalls
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 24480c2d95da..e4e0523102e2 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -48,6 +48,7 @@
 #endif
 
 #define __ARCH_WANT_SYS_CLONE
+#define __ARCH_WANT_SYS_CLONE3
 
 #ifndef __COMPAT_SYSCALL_NR
 #include <uapi/asm/unistd.h>
diff --git a/arch/x86/include/asm/unistd.h b/arch/x86/include/asm/unistd.h
index 146859efd83c..097589753fec 100644
--- a/arch/x86/include/asm/unistd.h
+++ b/arch/x86/include/asm/unistd.h
@@ -54,5 +54,6 @@
 # define __ARCH_WANT_SYS_FORK
 # define __ARCH_WANT_SYS_VFORK
 # define __ARCH_WANT_SYS_CLONE
+# define __ARCH_WANT_SYS_CLONE3
 
 #endif /* _ASM_X86_UNISTD_H */
diff --git a/arch/xtensa/include/asm/unistd.h b/arch/xtensa/include/asm/unistd.h
index 30af4dc3ce7b..b52236245e51 100644
--- a/arch/xtensa/include/asm/unistd.h
+++ b/arch/xtensa/include/asm/unistd.h
@@ -3,6 +3,7 @@
 #define _XTENSA_UNISTD_H
 
 #define __ARCH_WANT_SYS_CLONE
+#define __ARCH_WANT_SYS_CLONE3
 #include <uapi/asm/unistd.h>
 
 #define __ARCH_WANT_NEW_STAT
diff --git a/kernel/fork.c b/kernel/fork.c
index 08ff131f26b4..98abea995629 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2490,7 +2490,9 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
 
 	return _do_fork(&args);
 }
+#endif
 
+#ifdef __ARCH_WANT_SYS_CLONE3
 noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 					      struct clone_args __user *uargs,
 					      size_t size)
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 4d9ae5ea6caf..34b76895b81e 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -137,6 +137,8 @@ COND_SYSCALL(capset);
 /* kernel/exit.c */
 
 /* kernel/fork.c */
+/* __ARCH_WANT_SYS_CLONE3 */
+COND_SYSCALL(clone3);
 
 /* kernel/futex.c */
 COND_SYSCALL(futex);