riscv: Implement syscall wrappers

Commit f0bddf50586d ("riscv: entry: Convert to generic entry") moved
syscall handling to C code, which exposed function pointer type
mismatches that trip fine-grained forward-edge Control-Flow Integrity
(CFI) checks as syscall handlers are all called through the same
syscall_t pointer type. To fix the type mismatches, implement pt_regs
based syscall wrappers similarly to x86 and arm64.

This patch is based on arm64 syscall wrappers added in commit
4378a7d4be30 ("arm64: implement syscall wrappers"), where the main goal
was to minimize the risk of userspace-controlled values being used
under speculation. This may be a concern for riscv in future as well.

Following other architectures, the syscall wrappers generate three
functions for each syscall; __riscv_<compat_>sys_<name> takes a pt_regs
pointer and extracts arguments from registers, __se_<compat_>sys_<name>
is a sign-extension wrapper that casts the long arguments to the
correct types for the real syscall implementation, which is named
__do_<compat_>sys_<name>.

Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20230710183544.999540-9-samitolvanen@google.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 87 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/syscall_wrapper.h b/arch/riscv/include/asm/syscall_wrapper.h
new file mode 100644
index 000000000000..1d7942c8a6cb
--- /dev/null
+++ b/arch/riscv/include/asm/syscall_wrapper.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * syscall_wrapper.h - riscv specific wrappers to syscall definitions
+ *
+ * Based on arch/arm64/include/syscall_wrapper.h
+ */
+
+#ifndef __ASM_SYSCALL_WRAPPER_H
+#define __ASM_SYSCALL_WRAPPER_H
+
+#include <asm/ptrace.h>
+
+asmlinkage long __riscv_sys_ni_syscall(const struct pt_regs *);
+
+#define SC_RISCV_REGS_TO_ARGS(x, ...)				\
+	__MAP(x,__SC_ARGS					\
+	      ,,regs->orig_a0,,regs->a1,,regs->a2		\
+	      ,,regs->a3,,regs->a4,,regs->a5,,regs->a6)
+
+#ifdef CONFIG_COMPAT
+
+#define COMPAT_SYSCALL_DEFINEx(x, name, ...)						\
+	asmlinkage long __riscv_compat_sys##name(const struct pt_regs *regs);		\
+	ALLOW_ERROR_INJECTION(__riscv_compat_sys##name, ERRNO);				\
+	static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__));		\
+	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
+	asmlinkage long __riscv_compat_sys##name(const struct pt_regs *regs)		\
+	{										\
+		return __se_compat_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__));	\
+	}										\
+	static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))		\
+	{										\
+		return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));	\
+	}										\
+	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
+
+#define COMPAT_SYSCALL_DEFINE0(sname)							\
+	asmlinkage long __riscv_compat_sys_##sname(const struct pt_regs *__unused);	\
+	ALLOW_ERROR_INJECTION(__riscv_compat_sys_##sname, ERRNO);			\
+	asmlinkage long __riscv_compat_sys_##sname(const struct pt_regs *__unused)
+
+#define COND_SYSCALL_COMPAT(name) 							\
+	asmlinkage long __weak __riscv_compat_sys_##name(const struct pt_regs *regs);	\
+	asmlinkage long __weak __riscv_compat_sys_##name(const struct pt_regs *regs)	\
+	{										\
+		return sys_ni_syscall();						\
+	}
+
+#define COMPAT_SYS_NI(name) \
+	SYSCALL_ALIAS(__riscv_compat_sys_##name, sys_ni_posix_timers);
+
+#endif /* CONFIG_COMPAT */
+
+#define __SYSCALL_DEFINEx(x, name, ...)						\
+	asmlinkage long __riscv_sys##name(const struct pt_regs *regs);		\
+	ALLOW_ERROR_INJECTION(__riscv_sys##name, ERRNO);			\
+	static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__));		\
+	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
+	asmlinkage long __riscv_sys##name(const struct pt_regs *regs)		\
+	{									\
+		return __se_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__));	\
+	}									\
+	static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))		\
+	{									\
+		long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));	\
+		__MAP(x,__SC_TEST,__VA_ARGS__);					\
+		__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__));		\
+		return ret;							\
+	}									\
+	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
+
+#define SYSCALL_DEFINE0(sname)							\
+	SYSCALL_METADATA(_##sname, 0);						\
+	asmlinkage long __riscv_sys_##sname(const struct pt_regs *__unused);	\
+	ALLOW_ERROR_INJECTION(__riscv_sys_##sname, ERRNO);			\
+	asmlinkage long __riscv_sys_##sname(const struct pt_regs *__unused)
+
+#define COND_SYSCALL(name)							\
+	asmlinkage long __weak __riscv_sys_##name(const struct pt_regs *regs);	\
+	asmlinkage long __weak __riscv_sys_##name(const struct pt_regs *regs)	\
+	{									\
+		return sys_ni_syscall();					\
+	}
+
+#define SYS_NI(name) SYSCALL_ALIAS(__riscv_sys_##name, sys_ni_posix_timers);
+
+#endif /* __ASM_SYSCALL_WRAPPER_H */