PKGBUILDs/core/linux-odroid-c2/0007-arm64-ptrace-add-PTRACE_SET_SYSCALL.patch

From 896ccdd6bccc7698324c19c013f8fedd72142484 Mon Sep 17 00:00:00 2001
From: AKASHI Takahiro <takahiro.akashi@linaro.org>
Date: Thu, 21 Aug 2014 17:56:40 +0900
Subject: [PATCH 07/12] arm64: ptrace: add PTRACE_SET_SYSCALL

To allow tracer to be able to change/skip a system call by re-writing
a syscall number, there are several approaches:

(1) modify x8 register with ptrace(PTRACE_SETREGSET), and handle this case
    later on in syscall_trace_enter(), or
(2) support ptrace(PTRACE_SET_SYSCALL) as on arm

Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to
tracer as well as that secure_computing() expects a changed syscall number
to be visible, especially case of -1, before this function returns in
syscall_trace_enter(), we'd better take (2).

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/arm64/include/uapi/asm/ptrace.h |  1 +
 arch/arm64/kernel/ptrace.c           | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index c136fd53c847..164e2bbe9afd 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -23,6 +23,7 @@
 
 #include <asm/hwcap.h>
 
+#define PTRACE_SET_SYSCALL	23
 
 /*
  * PSR bits
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 53bdc598d1c1..6ef1e17d9c5b 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1093,7 +1093,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 long arch_ptrace(struct task_struct *child, long request,
 		 unsigned long addr, unsigned long data)
 {
-	return ptrace_request(child, request, addr, data);
+	int ret;
+
+	switch (request) {
+		case PTRACE_SET_SYSCALL:
+			task_pt_regs(child)->syscallno = data;
+			ret = 0;
+			break;
+		default:
+			ret = ptrace_request(child, request, addr, data);
+			break;
+	}
+
+	return ret;
 }
 
 enum ptrace_syscall_dir {
-- 
2.19.0