[PATCH] arm64: fix compat syscall return truncation

[Mark Rutland]

TODO: explain this.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: He Zhe <zhe.he@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: weiyuchen <weiyuchen3@xxxxxxxxxx>
---
 arch/arm64/include/asm/ptrace.h  | 12 +++++++++++-
 arch/arm64/include/asm/syscall.h | 19 ++++++++++---------
 arch/arm64/kernel/ptrace.c       |  2 +-
 arch/arm64/kernel/signal.c       |  3 ++-
 arch/arm64/kernel/syscall.c      |  9 +++------
 5 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index e58bca832dff..41b332c054ab 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -320,7 +320,17 @@ static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
 
 static inline unsigned long regs_return_value(struct pt_regs *regs)
 {
-	return regs->regs[0];
+	unsigned long val = regs->regs[0];
+
+	/*
+	 * Audit currently uses regs_return_value() instead of
+	 * syscall_get_return_value(). Apply the same sign-extension here until
+	 * audit is updated to use syscall_get_return_value().
+	 */
+	if (compat_user_mode(regs))
+		val = sign_extend64(val, 31);
+
+	return val;
 }
 
 static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index cfc0672013f6..03e20895453a 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -29,22 +29,23 @@ static inline void syscall_rollback(struct task_struct *task,
 	regs->regs[0] = regs->orig_x0;
 }
 
-
-static inline long syscall_get_error(struct task_struct *task,
-				     struct pt_regs *regs)
+static inline long syscall_get_return_value(struct task_struct *task,
+					    struct pt_regs *regs)
 {
-	unsigned long error = regs->regs[0];
+	unsigned long val = regs->regs[0];
 
 	if (is_compat_thread(task_thread_info(task)))
-		error = sign_extend64(error, 31);
+		val = sign_extend64(val, 31);
 
-	return IS_ERR_VALUE(error) ? error : 0;
+	return val;
 }
 
-static inline long syscall_get_return_value(struct task_struct *task,
-					    struct pt_regs *regs)
+static inline long syscall_get_error(struct task_struct *task,
+				     struct pt_regs *regs)
 {
-	return regs->regs[0];
+	unsigned long error = syscall_get_return_value(task, regs);
+
+	return IS_ERR_VALUE(error) ? error : 0;
 }
 
 static inline void syscall_set_return_value(struct task_struct *task,
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 499b6b2f9757..b381a1ee9ea7 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1862,7 +1862,7 @@ void syscall_trace_exit(struct pt_regs *regs)
 	audit_syscall_exit(regs);
 
 	if (flags & _TIF_SYSCALL_TRACEPOINT)
-		trace_sys_exit(regs, regs_return_value(regs));
+		trace_sys_exit(regs, syscall_get_return_value(current, regs));
 
 	if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 53c2c85efb34..62e273b2d83f 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -29,6 +29,7 @@
 #include <asm/unistd.h>
 #include <asm/fpsimd.h>
 #include <asm/ptrace.h>
+#include <asm/syscall.h>
 #include <asm/signal32.h>
 #include <asm/traps.h>
 #include <asm/vdso.h>
@@ -890,7 +891,7 @@ static void do_signal(struct pt_regs *regs)
 		     retval == -ERESTART_RESTARTBLOCK ||
 		     (retval == -ERESTARTSYS &&
 		      !(ksig.ka.sa.sa_flags & SA_RESTART)))) {
-			regs->regs[0] = -EINTR;
+			syscall_set_return_value(current, regs, -EINTR, 0);
 			regs->pc = continue_addr;
 		}
 
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 263d6c1a525f..50a0f1a38e84 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -54,10 +54,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
 		ret = do_ni_syscall(regs, scno);
 	}
 
-	if (is_compat_task())
-		ret = lower_32_bits(ret);
-
-	regs->regs[0] = ret;
+	syscall_set_return_value(current, regs, 0, ret);
 
 	/*
 	 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
@@ -115,7 +112,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 		 * syscall. do_notify_resume() will send a signal to userspace
 		 * before the syscall is restarted.
 		 */
-		regs->regs[0] = -ERESTARTNOINTR;
+		syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
 		return;
 	}
 
@@ -136,7 +133,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 		 * anyway.
 		 */
 		if (scno == NO_SYSCALL)
-			regs->regs[0] = -ENOSYS;
+			syscall_set_return_value(current, regs, -ENOSYS, 0);
 		scno = syscall_trace_enter(regs);
 		if (scno == NO_SYSCALL)
 			goto trace_exit;
-- 
2.11.0