Re: [RFC PATCH 2/3] tracing/syscalls: add handling for compat tasks

[Andy Lutomirski <luto@amacapital.net>]

On Mon, Sep 12, 2016 at 10:41 PM, Marcin Nowakowski
<marcin.nowakowski@imgtec.com> wrote:
> Hi Andy,
>
> Thanks for your review and the comments, I'll address them in a next
> iteration. Do you have any other comments on the complete patchset?

It seems reasonable to me.

>
> On 12.09.2016 19:35, Andy Lutomirski wrote:
>>
>> On Sep 9, 2016 1:04 AM, "Marcin Nowakowski"
>> <marcin.nowakowski@imgtec.com> wrote:
>>>
>>>
>>> Extend the syscall tracing subsystem by adding a handler for compat
>>> tasks. For some architectures, where compat tasks' syscall numbers have
>>> an exclusive set of syscall numbers, this already works since the
>>> removal of syscall_nr.
>>> Architectures where the same syscall may use a different syscall number
>>> for compat tasks need to define ARCH_COMPAT_SYSCALL_NUMBERS_OVERLAP and
>>> define a method arch_trace_is_compat_syscall(struct pt_regs*) that tells
>>> if a current task is a compat one.
>>> For architectures that define ARCH_COMPAT_SYSCALL_NUMBERS_OVERLAP the
>>> number of trace event files is doubled and all syscall trace events are
>>> identified by the syscall number offset by NR_syscalls.
>>>
>>> Note that as this patch series is posted as an RFC, this currently only
>>> includes arch updates for MIPS and x86 (and has only been tested on
>>> MIPS and x86_64). I will work on updating other arch trees after this
>>> solution is reviewed.
>>
>>
>> I bet you didn't test x32 -- see below :)
>
>
> Indeed ... I've tried with x86_64 and 32-bit x86, but not x32 syscalls. I
> will review that part.
>
>>>
>>> Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
>>>
>>> ---
>>>  arch/mips/kernel/ftrace.c     |   4 +-
>>>  arch/x86/include/asm/ftrace.h |  10 +---
>>>  arch/x86/kernel/ftrace.c      |  14 ++++++
>>>  include/linux/ftrace.h        |   2 +-
>>>  kernel/trace/trace.h          |  11 +++-
>>>  kernel/trace/trace_syscalls.c | 113
>>> +++++++++++++++++++++++++-----------------
>>>  6 files changed, 94 insertions(+), 60 deletions(-)
>>>
>>> diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
>>> index 937c54b..e150cf6 100644
>>> --- a/arch/mips/kernel/ftrace.c
>>> +++ b/arch/mips/kernel/ftrace.c
>>> @@ -412,7 +412,7 @@ out:
>>>  #ifdef CONFIG_FTRACE_SYSCALLS
>>>
>>>  #ifdef CONFIG_32BIT
>>> -unsigned long __init arch_syscall_addr(int nr)
>>> +unsigned long __init arch_syscall_addr(int nr, int compat)
>>>  {
>>>         return (unsigned long)sys_call_table[nr - __NR_O32_Linux];
>>>  }
>>> @@ -420,7 +420,7 @@ unsigned long __init arch_syscall_addr(int nr)
>>>
>>>  #ifdef CONFIG_64BIT
>>>
>>> -unsigned long __init arch_syscall_addr(int nr)
>>> +unsigned long __init arch_syscall_addr(int nr, int compat)
>>
>>
>> bool compat?
>
>
> Yes, that should make the intention more clear.
>
>>>  {
>>>  #ifdef CONFIG_MIPS32_N32
>>>         if (nr >= __NR_N32_Linux && nr <= __NR_N32_Linux +
>>> __NR_N32_Linux_syscalls)
>>> diff --git a/arch/x86/include/asm/ftrace.h
>>> b/arch/x86/include/asm/ftrace.h
>>> index a4820d4..a24a21c 100644
>>> --- a/arch/x86/include/asm/ftrace.h
>>> +++ b/arch/x86/include/asm/ftrace.h
>>> @@ -47,15 +47,7 @@ int ftrace_int3_handler(struct pt_regs *regs);
>>>  #if defined(CONFIG_FTRACE_SYSCALLS) && defined(CONFIG_IA32_EMULATION)
>>>  #include <asm/compat.h>
>>>
>>> -/*
>>> - * Because ia32 syscalls do not map to x86_64 syscall numbers
>>> - * this screws up the trace output when tracing a ia32 task.
>>> - * Instead of reporting bogus syscalls, just do not trace them.
>>> - *
>>> - * If the user really wants these, then they should use the
>>> - * raw syscall tracepoints with filtering.
>>> - */
>>> -#define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS 1
>>> +#define ARCH_COMPAT_SYSCALL_NUMBERS_OVERLAP 1
>>>  static inline bool arch_trace_is_compat_syscall(struct pt_regs *regs)
>>>  {
>>>         if (in_compat_syscall())
>>
>>
>> This isn't your fault obviously, but shouldn't that be in_ia32_syscall()?
>
>
> Thanks for pointing this out - I'll need to review this part of code a bit
> more.
>
> Marcin



-- 
Andy Lutomirski
AMA Capital Management, LLC