orig_x0 is recorded at the start of the syscall entry and then it is
used for resetting the argument back to its original value during
syscall restarts.
If orig_x0 isn't available from user-space, this makes it tricky to
manage arguments of restarted system calls.
Cc: Keno Fischer <[email protected]>
Signed-off-by: Andrei Vagin <[email protected]>
---
arch/arm64/include/asm/ptrace.h | 2 +-
arch/arm64/include/uapi/asm/ptrace.h | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index e58bca832dff..d4cdf98ac003 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -183,9 +183,9 @@ struct pt_regs {
u64 sp;
u64 pc;
u64 pstate;
+ u64 orig_x0;
};
};
- u64 orig_x0;
#ifdef __AARCH64EB__
u32 unused2;
s32 syscallno;
diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 758ae984ff97..3c118c5b0893 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -90,6 +90,7 @@ struct user_pt_regs {
__u64 sp;
__u64 pc;
__u64 pstate;
+ __u64 orig_x0;
};
struct user_fpsimd_state {
--
2.29.2
On Mon, Mar 22, 2021 at 03:50:50PM -0700, Andrei Vagin wrote:
> diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
> index 758ae984ff97..3c118c5b0893 100644
> --- a/arch/arm64/include/uapi/asm/ptrace.h
> +++ b/arch/arm64/include/uapi/asm/ptrace.h
> @@ -90,6 +90,7 @@ struct user_pt_regs {
> __u64 sp;
> __u64 pc;
> __u64 pstate;
> + __u64 orig_x0;
> };
That's a UAPI change, likely to go wrong. For example, a
ptrace(PTRACE_GETREGSET, pid, REGSET_GPR, data) would write past the end
of an old struct user_pt_regs in the debugger.
--
Catalin
On Fri, Mar 26, 2021 at 11:28 AM Catalin Marinas
<[email protected]> wrote:
>
> On Mon, Mar 22, 2021 at 03:50:50PM -0700, Andrei Vagin wrote:
> > diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
> > index 758ae984ff97..3c118c5b0893 100644
> > --- a/arch/arm64/include/uapi/asm/ptrace.h
> > +++ b/arch/arm64/include/uapi/asm/ptrace.h
> > @@ -90,6 +90,7 @@ struct user_pt_regs {
> > __u64 sp;
> > __u64 pc;
> > __u64 pstate;
> > + __u64 orig_x0;
> > };
>
> That's a UAPI change, likely to go wrong. For example, a
> ptrace(PTRACE_GETREGSET, pid, REGSET_GPR, data) would write past the end
> of an old struct user_pt_regs in the debugger.
ptrace(PTRACE_GETREGSET, ...) receives iovec:
ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov)
iov contains a pointer to a buffer and its size and the kernel fills
only the part that fits the buffer.
I think this interface was invented to allow extending structures
without breaking backward compatibility.
>
> --
> Catalin
On Fri, Mar 26, 2021 at 05:35:19PM -0700, Andrei Vagin wrote:
> On Fri, Mar 26, 2021 at 11:28 AM Catalin Marinas
> <[email protected]> wrote:
> >
> > On Mon, Mar 22, 2021 at 03:50:50PM -0700, Andrei Vagin wrote:
> > > diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
> > > index 758ae984ff97..3c118c5b0893 100644
> > > --- a/arch/arm64/include/uapi/asm/ptrace.h
> > > +++ b/arch/arm64/include/uapi/asm/ptrace.h
> > > @@ -90,6 +90,7 @@ struct user_pt_regs {
> > > __u64 sp;
> > > __u64 pc;
> > > __u64 pstate;
> > > + __u64 orig_x0;
> > > };
> >
> > That's a UAPI change, likely to go wrong. For example, a
> > ptrace(PTRACE_GETREGSET, pid, REGSET_GPR, data) would write past the end
> > of an old struct user_pt_regs in the debugger.
>
> ptrace(PTRACE_GETREGSET, ...) receives iovec:
> ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov)
>
> iov contains a pointer to a buffer and its size and the kernel fills
> only the part that fits the buffer.
> I think this interface was invented to allow extending structures
> without breaking backward compatibility.
You are right here, it doesn't write past the end of the iov buffer.
However, it's still an ABI change. An unaware program using a newer
user_pt_regs but running on an older kernel may be surprised that the
updated iov.len is smaller than sizeof (struct user_pt_regs).
Changing this structure also changes the core dump format, see ELF_NGREG
and ELF_CORE_COPY_REGS. Maybe this doesn't matter much either since the
ELF note would have size information but I'd prefer if we didn't modify
this structure.
--
Catalin