syscalls/core: Prepare CONFIG_ARCH_HAS_SYSCALL_WRAPPER=y for compat syscalls

It may be useful for an architecture to override the definitions of the
COMPAT_SYSCALL_DEFINE0() and __COMPAT_SYSCALL_DEFINEx() macros in
<linux/compat.h>, in particular to use a different calling convention
for syscalls. This patch provides a mechanism to do so, based on the
previously introduced CONFIG_ARCH_HAS_SYSCALL_WRAPPER. If it is enabled,
<asm/sycall_wrapper.h> is included in <linux/compat.h> and may be used
to define the macros mentioned above. Moreover, as the syscall calling
convention may be different if CONFIG_ARCH_HAS_SYSCALL_WRAPPER is set,
the compat syscall function prototypes in <linux/compat.h> are #ifndef'd
out in that case.

As some of the syscalls and/or compat syscalls may not be present,
the COND_SYSCALL() and COND_SYSCALL_COMPAT() macros in kernel/sys_ni.c
as well as the SYS_NI() and COMPAT_SYS_NI() macros in
kernel/time/posix-stubs.c can be re-defined in <asm/syscall_wrapper.h> iff
CONFIG_ARCH_HAS_SYSCALL_WRAPPER is enabled.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180405095307.3730-5-linux@dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 20 insertions, 0 deletions

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 6cafc008f6db..9791364925dc 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -5,6 +5,11 @@
 
 #include <asm/unistd.h>
 
+#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
+/* Architectures may override COND_SYSCALL and COND_SYSCALL_COMPAT */
+#include <asm/syscall_wrapper.h>
+#endif /* CONFIG_ARCH_HAS_SYSCALL_WRAPPER */
+
 /*  we can't #include <linux/syscalls.h> here,
     but tell gcc to not warn with -Wmissing-prototypes  */
 asmlinkage long sys_ni_syscall(void);
@@ -17,8 +22,13 @@ asmlinkage long sys_ni_syscall(void)
         return -ENOSYS;
 }
 
+#ifndef COND_SYSCALL
 #define COND_SYSCALL(name) cond_syscall(sys_##name)
+#endif /* COND_SYSCALL */
+
+#ifndef COND_SYSCALL_COMPAT
 #define COND_SYSCALL_COMPAT(name) cond_syscall(compat_sys_##name)
+#endif /* COND_SYSCALL_COMPAT */
 
 /*
  * This list is kept in the same order as include/uapi/asm-generic/unistd.h.
diff --git a/kernel/time/posix-stubs.c b/kernel/time/posix-stubs.c
index b258bee13b02..69a937c3cd81 100644
--- a/kernel/time/posix-stubs.c
+++ b/kernel/time/posix-stubs.c
@@ -19,6 +19,11 @@
 #include <linux/posix-timers.h>
 #include <linux/compat.h>
 
+#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
+/* Architectures may override SYS_NI and COMPAT_SYS_NI */
+#include <asm/syscall_wrapper.h>
+#endif
+
 asmlinkage long sys_ni_posix_timers(void)
 {
         pr_err_once("process %d (%s) attempted a POSIX timer syscall "
@@ -27,8 +32,13 @@ asmlinkage long sys_ni_posix_timers(void)
         return -ENOSYS;
 }
 
+#ifndef SYS_NI
 #define SYS_NI(name)  SYSCALL_ALIAS(sys_##name, sys_ni_posix_timers)
+#endif
+
+#ifndef COMPAT_SYS_NI
 #define COMPAT_SYS_NI(name)  SYSCALL_ALIAS(compat_sys_##name, sys_ni_posix_timers)
+#endif
 
 SYS_NI(timer_create);
 SYS_NI(timer_gettime);