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Date:   Fri, 13 Sep 2019 14:00:18 -0700
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Subject: [PATCH 4/4] x86: fix function types in COND_SYSCALL
From:   Sami Tolvanen <samitolvanen@google.com>
To:     Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Kees Cook <keescook@chromium.org>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Sami Tolvanen <samitolvanen@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Define a weak function in COND_SYSCALL instead of a weak alias to
sys_ni_syscall, which has an incompatible type. This fixes indirect
call mismatches with Control-Flow Integrity (CFI) checking.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/x86/include/asm/syscall_wrapper.h | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
index 90eb70df0b18..9a595a544017 100644
--- a/arch/x86/include/asm/syscall_wrapper.h
+++ b/arch/x86/include/asm/syscall_wrapper.h
@@ -6,6 +6,8 @@
 #ifndef _ASM_X86_SYSCALL_WRAPPER_H
 #define _ASM_X86_SYSCALL_WRAPPER_H
 
+struct pt_regs;
+
 /* Mapping of registers to parameters for syscalls on x86-64 and x32 */
 #define SC_X86_64_REGS_TO_ARGS(x, ...)					\
 	__MAP(x,__SC_ARGS						\
@@ -56,9 +58,15 @@
 	SYSCALL_ALIAS(__ia32_sys_##sname, __x64_sys_##sname);		\
 	asmlinkage long __x64_sys_##sname(const struct pt_regs *__unused)
 
-#define COND_SYSCALL(name)						\
-	cond_syscall(__x64_sys_##name);					\
-	cond_syscall(__ia32_sys_##name)
+#define COND_SYSCALL(name)							\
+	asmlinkage __weak long __x64_sys_##name(const struct pt_regs *__unused)	\
+	{									\
+		return sys_ni_syscall();					\
+	}									\
+	asmlinkage __weak long __ia32_sys_##name(const struct pt_regs *__unused)\
+	{									\
+		return sys_ni_syscall();					\
+	}
 
 #define SYS_NI(name)							\
 	SYSCALL_ALIAS(__x64_sys_##name, sys_ni_posix_timers);		\
@@ -190,7 +198,11 @@
 #endif
 
 #ifndef COND_SYSCALL
-#define COND_SYSCALL(name) cond_syscall(__x64_sys_##name)
+#define COND_SYSCALL(name) 							\
+	asmlinkage __weak long __x64_sys_##name(const struct pt_regs *__unused)	\
+	{									\
+		return sys_ni_syscall();					\
+	}
 #endif
 
 #ifndef SYS_NI
@@ -202,7 +214,6 @@
  * For VSYSCALLS, we need to declare these three syscalls with the new
  * pt_regs-based calling convention for in-kernel use.
  */
-struct pt_regs;
 asmlinkage long __x64_sys_getcpu(const struct pt_regs *regs);
 asmlinkage long __x64_sys_gettimeofday(const struct pt_regs *regs);
 asmlinkage long __x64_sys_time(const struct pt_regs *regs);
-- 
2.23.0.237.gc6a4ce50a0-goog