On 08/22/2014 01:47 AM, Kees Cook wrote:
On Thu, Aug 21, 2014 at 3:56 AM, AKASHI Takahiro takahiro.akashi@linaro.org wrote:
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
Thanks, I like having this on both arm and arm64.
Yeah, having this simplified the code of syscall_trace_enter() a bit, but also imposes some restriction on arm64, too.
I wonder if other archs should add this option too.
Do you think so? I assumed that SET_SYSCALL is to be avoided if possible.
I also think that SET_SYSCALL should take an extra argument for a return value just in case of -1 (or we have SKIP_SYSCALL?).
-Takahiro AKASHI
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 6913643..49c6174 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 0310811..8876049 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1077,7 +1077,19 @@ 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 {
-- 1.7.9.5