syscalls/x86: Use the correct function type for sys_ni_syscall

Use the correct function type for sys_ni_syscall() in system
call tables to fix indirect call mismatches with Control-Flow
Integrity (CFI) checking.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191008224049.115427-5-samitolvanen@google.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/syscall_32.c

@@ -10,13 +10,11 @@
 #ifdef CONFIG_IA32_EMULATION
 /* On X86_64, we use struct pt_regs * to pass parameters to syscalls */
 #define __SYSCALL_I386(nr, sym, qual) extern asmlinkage long sym(const struct pt_regs *);
-
-/* this is a lie, but it does not hurt as sys_ni_syscall just returns -EINVAL */
-extern asmlinkage long sys_ni_syscall(const struct pt_regs *);
-
+#define __sys_ni_syscall __ia32_sys_ni_syscall
 #else /* CONFIG_IA32_EMULATION */
 #define __SYSCALL_I386(nr, sym, qual) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
 extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
+#define __sys_ni_syscall sys_ni_syscall
 #endif /* CONFIG_IA32_EMULATION */
 
 #include <asm/syscalls_32.h>
@@ -29,6 +27,6 @@ __visible const sys_call_ptr_t ia32_sys_call_table[__NR_syscall_compat_max+1] =
 	 * Smells like a compiler bug -- it doesn't work
 	 * when the & below is removed.
 	 */
-	[0 ... __NR_syscall_compat_max] = &sys_ni_syscall,
+	[0 ... __NR_syscall_compat_max] = &__sys_ni_syscall,
 #include <asm/syscalls_32.h>
 };

arch/x86/entry/syscall_64.c

@@ -4,11 +4,17 @@
 #include <linux/linkage.h>
 #include <linux/sys.h>
 #include <linux/cache.h>
+#include <linux/syscalls.h>
 #include <asm/asm-offsets.h>
 #include <asm/syscall.h>
 
-/* this is a lie, but it does not hurt as sys_ni_syscall just returns -EINVAL */
-extern asmlinkage long sys_ni_syscall(const struct pt_regs *);
+extern asmlinkage long sys_ni_syscall(void);
+
+SYSCALL_DEFINE0(ni_syscall)
+{
+	return sys_ni_syscall();
+}
+
 #define __SYSCALL_64(nr, sym, qual) extern asmlinkage long sym(const struct pt_regs *);
 #define __SYSCALL_X32(nr, sym, qual) __SYSCALL_64(nr, sym, qual)
 #include <asm/syscalls_64.h>
@@ -23,7 +29,7 @@ asmlinkage const sys_call_ptr_t sys_call_table[__NR_syscall_max+1] = {
 	 * Smells like a compiler bug -- it doesn't work
 	 * when the & below is removed.
 	 */
-	[0 ... __NR_syscall_max] = &sys_ni_syscall,
+	[0 ... __NR_syscall_max] = &__x64_sys_ni_syscall,
 #include <asm/syscalls_64.h>
 };
 
@@ -40,7 +46,7 @@ asmlinkage const sys_call_ptr_t x32_sys_call_table[__NR_syscall_x32_max+1] = {
 	 * Smells like a compiler bug -- it doesn't work
 	 * when the & below is removed.
 	 */
-	[0 ... __NR_syscall_x32_max] = &sys_ni_syscall,
+	[0 ... __NR_syscall_x32_max] = &__x64_sys_ni_syscall,
 #include <asm/syscalls_64.h>
 };
 

arch/x86/entry/syscalls/syscall_32.tbl

@@ -124,7 +124,7 @@
 110	i386	iopl			sys_iopl			__ia32_sys_iopl
 111	i386	vhangup			sys_vhangup			__ia32_sys_vhangup
 112	i386	idle
-113	i386	vm86old			sys_vm86old			sys_ni_syscall
+113	i386	vm86old			sys_vm86old			__ia32_sys_ni_syscall
 114	i386	wait4			sys_wait4			__ia32_compat_sys_wait4
 115	i386	swapoff			sys_swapoff			__ia32_sys_swapoff
 116	i386	sysinfo			sys_sysinfo			__ia32_compat_sys_sysinfo
@@ -177,7 +177,7 @@
 163	i386	mremap			sys_mremap			__ia32_sys_mremap
 164	i386	setresuid		sys_setresuid16			__ia32_sys_setresuid16
 165	i386	getresuid		sys_getresuid16			__ia32_sys_getresuid16
-166	i386	vm86			sys_vm86			sys_ni_syscall
+166	i386	vm86			sys_vm86			__ia32_sys_ni_syscall
 167	i386	query_module
 168	i386	poll			sys_poll			__ia32_sys_poll
 169	i386	nfsservctl