riscv: Fix syscall wrapper for >word-size arguments

The current syscall wrapper macros break 64-bit arguments on
rv32 because they only guarantee the first N input registers are
passed to syscalls that accept N arguments. According to the
calling convention, values twice the word size reside in register
pairs and as a result, syscall arguments don't always have a
direct register mapping on rv32.

Instead of using `__MAP(x,__SC_LONG,__VA_ARGS__)` to declare the
type of the `__se(_compat)_sys_*` functions on rv32, change the
function declarations to accept `ulong` arguments and alias them
to the actual syscall implementations, similarly to the existing
macros in include/linux/syscalls.h. This matches previous
behavior and ensures registers are passed to syscalls as-is, no
matter which argument types they expect.

Fixes: 08d0ce3 ("riscv: Implement syscall wrappers")
Reported-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20240311193143.2981310-2-samitolvanen@google.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: samitolvanen

arch/riscv/include/asm/syscall_wrapper.h

@@ -12,25 +12,51 @@
 
 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		\
+#ifdef CONFIG_64BIT
+
+#define __SYSCALL_SE_DEFINEx(x, prefix, name, ...)					\
+	static long __se_##prefix##name(__MAP(x,__SC_LONG,__VA_ARGS__));		\
+	static long __se_##prefix##name(__MAP(x,__SC_LONG,__VA_ARGS__))
+
+#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)
 
+#else
+/*
+ * Use type aliasing to ensure registers a0-a6 are correctly passed to the syscall
+ * implementation when >word-size arguments are used.
+ */
+#define __SYSCALL_SE_DEFINEx(x, prefix, name, ...)					\
+	__diag_push();									\
+	__diag_ignore(GCC, 8, "-Wattribute-alias",					\
+			"Type aliasing is used to sanitize syscall arguments");		\
+	static long __se_##prefix##name(ulong, ulong, ulong, ulong, ulong, ulong, 	\
+					ulong)						\
+			__attribute__((alias(__stringify(___se_##prefix##name))));	\
+	__diag_pop();									\
+	static long noinline ___se_##prefix##name(__MAP(x,__SC_LONG,__VA_ARGS__));	\
+	static long ___se_##prefix##name(__MAP(x,__SC_LONG,__VA_ARGS__))
+
+#define SC_RISCV_REGS_TO_ARGS(x, ...) \
+	regs->orig_a0,regs->a1,regs->a2,regs->a3,regs->a4,regs->a5,regs->a6
+
+#endif /* CONFIG_64BIT */
+
 #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)		\
+	__SYSCALL_SE_DEFINEx(x, compat_sys, name, __VA_ARGS__)				\
 	{										\
-		return __se_compat_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__));	\
+		return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));	\
 	}										\
-	static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))		\
+	asmlinkage long __riscv_compat_sys##name(const struct pt_regs *regs)		\
 	{										\
-		return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));	\
+		return __se_compat_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__));	\
 	}										\
 	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 
@@ -51,19 +77,18 @@ asmlinkage long __riscv_sys_ni_syscall(const struct pt_regs *);
 #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__))		\
+	__SYSCALL_SE_DEFINEx(x, sys, name, __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;							\
 	}									\
+	asmlinkage long __riscv_sys##name(const struct pt_regs *regs)		\
+	{									\
+		return __se_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__));	\
+	}									\
 	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 
 #define SYSCALL_DEFINE0(sname)							\