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

[Marcin Nowakowski]

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?

On 12.09.2016 19:35, Andy Lutomirski wrote:
> On Sep 9, 2016 1:04 AM, "Marcin Nowakowski"
> <marcin.nowakowski@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > ---
> >  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