Re: [Qemu-trivial] [PATCH v2] monitor: Fix crashes when using HMP commands without CPU

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Thomas Huth (thuth@redhat.com) wrote:
> When running certain HMP commands ("info registers", "info cpustats",
> "nmi", "memsave" or dumping virtual memory) with the "none" machine,
> QEMU crashes with a segmentation fault. This happens because the "none"
> machine does not have any CPUs by default, but these HMP commands did
> not check for a valid CPU pointer yet. Add such checks now, so we get
> an error message about the missing CPU instead.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v2:
>  - Added more checks to cover "nmi" and "memsave", too
> 
>  hmp.c     |  8 +++++++-
>  monitor.c | 37 +++++++++++++++++++++++++++++++------
>  2 files changed, 38 insertions(+), 7 deletions(-)
> 
> diff --git a/hmp.c b/hmp.c
> index b869617..b1c503a 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -1013,8 +1013,14 @@ void hmp_memsave(Monitor *mon, const QDict *qdict)
>      const char *filename = qdict_get_str(qdict, "filename");
>      uint64_t addr = qdict_get_int(qdict, "val");
>      Error *err = NULL;
> +    int cpu_index = monitor_get_cpu_index();
>  
> -    qmp_memsave(addr, size, filename, true, monitor_get_cpu_index(), &err);
> +    if (cpu_index < 0) {
> +        monitor_printf(mon, "No CPU available\n");
> +        return;
> +    }

OK, that includes UNASSIGNED_CPU_INDEX.

> +
> +    qmp_memsave(addr, size, filename, true, cpu_index, &err);
>      hmp_handle_error(mon, &err);
>  }
>  
> diff --git a/monitor.c b/monitor.c
> index 0841d43..74843eb 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -1025,6 +1025,9 @@ int monitor_set_cpu(int cpu_index)
>  CPUState *mon_get_cpu(void)
>  {
>      if (!cur_mon->mon_cpu) {
> +        if (!first_cpu) {
> +            return NULL;
> +        }
>          monitor_set_cpu(first_cpu->cpu_index);
>      }
>      cpu_synchronize_state(cur_mon->mon_cpu);
> @@ -1033,17 +1036,27 @@ CPUState *mon_get_cpu(void)
>  
>  CPUArchState *mon_get_cpu_env(void)
>  {
> -    return mon_get_cpu()->env_ptr;
> +    CPUState *cs = mon_get_cpu();
> +
> +    return cs ? cs->env_ptr : NULL;
>  }
>  
>  int monitor_get_cpu_index(void)
>  {
> -    return mon_get_cpu()->cpu_index;
> +    CPUState *cs = mon_get_cpu();
> +
> +    return cs ? cs->cpu_index : -1;
>  }

OK, do you think that should use UNASSIGNED_CPU_INDEX
explicitly rather than -1 ?

>  
>  static void hmp_info_registers(Monitor *mon, const QDict *qdict)
>  {
> -    cpu_dump_state(mon_get_cpu(), (FILE *)mon, monitor_fprintf, CPU_DUMP_FPU);
> +    CPUState *cs = mon_get_cpu();
> +
> +    if (!cs) {
> +        monitor_printf(mon, "No CPU available\n");
> +        return;
> +    }
> +    cpu_dump_state(cs, (FILE *)mon, monitor_fprintf, CPU_DUMP_FPU);
>  }
>  
>  static void hmp_info_jit(Monitor *mon, const QDict *qdict)
> @@ -1076,7 +1089,13 @@ static void hmp_info_history(Monitor *mon, const QDict *qdict)
>  
>  static void hmp_info_cpustats(Monitor *mon, const QDict *qdict)
>  {
> -    cpu_dump_statistics(mon_get_cpu(), (FILE *)mon, &monitor_fprintf, 0);
> +    CPUState *cs = mon_get_cpu();
> +
> +    if (!cs) {
> +        monitor_printf(mon, "No CPU available\n");
> +        return;
> +    }
> +    cpu_dump_statistics(cs, (FILE *)mon, &monitor_fprintf, 0);
>  }
>  
>  static void hmp_info_trace_events(Monitor *mon, const QDict *qdict)
> @@ -1235,6 +1254,12 @@ static void memory_dump(Monitor *mon, int count, int format, int wsize,
>      int l, line_size, i, max_digits, len;
>      uint8_t buf[16];
>      uint64_t v;
> +    CPUState *cs = mon_get_cpu();
> +
> +    if (!cs && (format == 'i' || !is_physical)) {
> +        monitor_printf(mon, "Can not dump without CPU\n");
> +        return;
> +    }
>  
>      if (format == 'i') {
>          int flags = 0;
> @@ -1264,7 +1289,7 @@ static void memory_dump(Monitor *mon, int count, int format, int wsize,
>          flags = msr_le << 16;
>          flags |= env->bfd_mach;
>  #endif
> -        monitor_disas(mon, mon_get_cpu(), addr, count, is_physical, flags);
> +        monitor_disas(mon, cs, addr, count, is_physical, flags);
>          return;
>      }
>  
> @@ -1303,7 +1328,7 @@ static void memory_dump(Monitor *mon, int count, int format, int wsize,
>          if (is_physical) {
>              cpu_physical_memory_read(addr, buf, l);
>          } else {
> -            if (cpu_memory_rw_debug(mon_get_cpu(), addr, buf, l, 0) < 0) {
> +            if (cpu_memory_rw_debug(cs, addr, buf, l, 0) < 0) {
>                  monitor_printf(mon, " Cannot access memory\n");
>                  break;
>              }
> -- 
> 1.8.3.1


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

I'm sure we'll find loads more similar cases where -M none breaks stuff.

(I see you've cc'd to trivial so I'll let them take it).

Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK