On 11/26/2014 09:41 PM, Will Deacon wrote:

Hi Akashi,

On Wed, Nov 26, 2014 at 04:49:46AM +0000, AKASHI Takahiro wrote:

quoted

This regeset is intended to be used to get and set a system call number
while tracing.
There was some discussion about possible approaches to do so:

(1) modify x8 register with ptrace(PTRACE_SETREGSET) indirectly,
     and update regs->syscallno later on in syscall_trace_enter(), or
(2) define a dedicated regset for this purpose as on s390, or
(3) support ptrace(PTRACE_SET_SYSCALL) as on arch/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,
especially case of -1, to be visible before this function returns in
syscall_trace_enter(), (1) doesn't work well.
We will take (2) since it looks much cleaner.

Signed-off-by: AKASHI Takahiro <redacted>
---
  arch/arm64/kernel/ptrace.c |   35 +++++++++++++++++++++++++++++++++++
  include/uapi/linux/elf.h   |    1 +
  2 files changed, 36 insertions(+)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 8a4ae8e..8b98781 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c

@@ -551,6 +551,32 @@ static int tls_set(struct task_struct *target, const struct user_regset *regset,
  	return ret;
  }

+static int system_call_get(struct task_struct *target,
+			   const struct user_regset *regset,
+			   unsigned int pos, unsigned int count,
+			   void *kbuf, void __user *ubuf)
+{
+	struct pt_regs *regs = task_pt_regs(target);
+
+	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+				   &regs->syscallno, 0, -1);

Does this work for big-endian machines? regs->syscallno is a u64, but the
regset defines it as an int. I think you need to copy to a temporary
register first.

Right. I will fix it.
Do you prefer to use s32, instead of int, like other regsets?


Thanks,
-Takahiro AKASHI

Will