linux-kernel - [PATCH] arm64: fix function types in COND

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Date:   Tue, 10 Sep 2019 15:40:44 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH] arm64: fix function types in COND_SYSCALL

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@...gle.com>
---
 arch/arm64/include/asm/syscall_wrapper.h | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/syscall_wrapper.h b/arch/arm64/include/asm/syscall_wrapper.h
index 507d0ee6bc69..06d880b3526c 100644
--- a/arch/arm64/include/asm/syscall_wrapper.h
+++ b/arch/arm64/include/asm/syscall_wrapper.h
@@ -8,6 +8,8 @@
 #ifndef __ASM_SYSCALL_WRAPPER_H
 #define __ASM_SYSCALL_WRAPPER_H
 
+struct pt_regs;
+
 #define SC_ARM64_REGS_TO_ARGS(x, ...)				\
 	__MAP(x,__SC_ARGS					\
 	      ,,regs->regs[0],,regs->regs[1],,regs->regs[2]	\
@@ -35,8 +37,11 @@
 	ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO);			\
 	asmlinkage long __arm64_compat_sys_##sname(const struct pt_regs *__unused)
 
-#define COND_SYSCALL_COMPAT(name) \
-	cond_syscall(__arm64_compat_sys_##name);
+#define COND_SYSCALL_COMPAT(name) 							\
+	asmlinkage long __weak __arm64_compat_sys_##name(const struct pt_regs *regs)	\
+	{										\
+		return sys_ni_syscall();						\
+	}
 
 #define COMPAT_SYS_NI(name) \
 	SYSCALL_ALIAS(__arm64_compat_sys_##name, sys_ni_posix_timers);
@@ -70,7 +75,11 @@
 #endif
 
 #ifndef COND_SYSCALL
-#define COND_SYSCALL(name) cond_syscall(__arm64_sys_##name)
+#define COND_SYSCALL(name)							\
+	asmlinkage long __weak __arm64_sys_##name(const struct pt_regs *regs)	\
+	{									\
+		return sys_ni_syscall();					\
+	}
 #endif
 
 #ifndef SYS_NI
-- 
2.23.0.162.g0b9fbb3734-goog