On 10/09/2014 12:30 AM, Kees Cook wrote:
On Wed, Oct 8, 2014 at 9:13 AM, Will Deacon <will.dea...@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 <keesc...@chromium.org>
Signed-off-by: AKASHI Takahiro <takahiro.aka...@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.
+1 :)
-Takahiro AKASHI
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
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