| Message ID | 20210322225053.428615-2-avagin@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64/ptrace: allow to get all registers on syscall traps | expand |
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.
On Fri, Mar 26, 2021 at 11:28 AM Catalin Marinas <catalin.marinas@arm.com> 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 > <catalin.marinas@arm.com> 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.
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 {
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 <keno@juliacomputing.com> Signed-off-by: Andrei Vagin <avagin@gmail.com> --- arch/arm64/include/asm/ptrace.h | 2 +- arch/arm64/include/uapi/asm/ptrace.h | 1 + 2 files changed, 2 insertions(+), 1 deletion(-)