On Wed, Oct 8, 2014 at 9:13 AM, Will Deacon will.deacon@arm.com wrote:
Hi Akashi,
On Thu, Oct 02, 2014 at 10:46:11AM +0100, AKASHI Takahiro 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).
Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.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 fe63ac5..2842f9f 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1082,7 +1082,19 @@ 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;}
I still don't understand why this needs to be in arch-specific code. Can't we implement this in generic code and get architectures to implement something like syscall_set_nr if they want the generic interface?
Personally, I'd rather see this land as-is in the arm64 tree, and then later optimize PTRACE_SET_SYSCALL out of arm/ and arm64/, especially since only these architectures implement this at the moment.
This is my plan for the asm-generic seccomp.h too -- I'd rather avoid touching other architectures in this series, as it's easier to review this way. Then we can optimize the code in a separate series, which will have those changes isolated, etc.
-Kees