[PATCH v4 2/2] arm64: syscall: Pass 'orig_x0' as first argument to native system call

[Will Deacon]

syscall_get_arguments() returns 'regs->orig_x0' for the first system
call argument so as to avoid aliasing with the syscall return value in
'regs->regs[0]' on the return path, however the actual syscall
invocation passes 'regs->regs[0]' as the first parameter.

Although the two registers should be kept in sync during syscall entry
for native tasks, pass 'regs->orig_x0' as the first syscall parameter
for consistency with the syscall argument APIs. Compat tasks continue to
use 'regs->regs[0]' for compatibility with the behaviour of the 32-bit
kernel.

Suggested-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
 arch/arm64/include/asm/syscall_wrapper.h | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/syscall_wrapper.h b/arch/arm64/include/asm/syscall_wrapper.h
index abb57bc54305..395152ef5372 100644
--- a/arch/arm64/include/asm/syscall_wrapper.h
+++ b/arch/arm64/include/asm/syscall_wrapper.h
@@ -10,13 +10,13 @@
 
 #include <asm/ptrace.h>
 
-#define SC_ARM64_REGS_TO_ARGS(x, ...)				\
+#ifdef CONFIG_COMPAT
+
+#define COMPAT_SC_ARM64_REGS_TO_ARGS(x, ...)			\
 	__MAP(x,__SC_ARGS					\
 	      ,,regs->regs[0],,regs->regs[1],,regs->regs[2]	\
 	      ,,regs->regs[3],,regs->regs[4],,regs->regs[5])
 
-#ifdef CONFIG_COMPAT
-
 #define COMPAT_SYSCALL_DEFINEx(x, name, ...)						\
 	asmlinkage long __arm64_compat_sys##name(const struct pt_regs *regs);		\
 	ALLOW_ERROR_INJECTION(__arm64_compat_sys##name, ERRNO);				\
@@ -24,7 +24,7 @@
 	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
 	asmlinkage long __arm64_compat_sys##name(const struct pt_regs *regs)		\
 	{										\
-		return __se_compat_sys##name(SC_ARM64_REGS_TO_ARGS(x,__VA_ARGS__));	\
+		return __se_compat_sys##name(COMPAT_SC_ARM64_REGS_TO_ARGS(x,__VA_ARGS__));	\
 	}										\
 	static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))		\
 	{										\
@@ -46,6 +46,11 @@
 
 #endif /* CONFIG_COMPAT */
 
+#define SC_ARM64_REGS_TO_ARGS(x, ...)				\
+	__MAP(x,__SC_ARGS					\
+	      ,,regs->orig_x0,,regs->regs[1],,regs->regs[2]	\
+	      ,,regs->regs[3],,regs->regs[4],,regs->regs[5])
+
 #define __SYSCALL_DEFINEx(x, name, ...)						\
 	asmlinkage long __arm64_sys##name(const struct pt_regs *regs);		\
 	ALLOW_ERROR_INJECTION(__arm64_sys##name, ERRNO);			\
-- 
2.55.0.508.g3f0d502094-goog