Re: [PATCH] proc: do not show VmExe bigger than total executable virtual memory

[Konstantin Khlebnikov]

On 11.10.2017 01:25, Andrew Morton wrote:
> On Fri, 06 Oct 2017 14:32:34 +0300 Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> wrote:
>
> > If start_code / end_code pointers are screwed then "VmExe" could be bigger
> > than total executable virtual memory and "VmLib" becomes negative:
> >
> > VmExe:	  294320 kB
> > VmLib:	18446744073709327564 kB
> >
> > VmExe and VmLib documented as text segment and shared library code size.
> >
> > Now their sum will be always equal to mm->exec_vm which sums size of
> > executable and not writable and not stack areas.
>
> When does this happen?  What causes start_code/end_code to get "screwed"?

I don't know exactly what happened.
I've seen this for huge (>2Gb) statically linked binary which has whole world inside.

For it start_code .. end_code range also covers one of rodata sections.
Probably this is bug in customized linker, elf loader or both.

Anyway CONFIG_CHECKPOINT_RESTORE allows to change these pointers,
thus we cannot trust them without validation.

> When these pointers are screwed, the result of end_code-start_code can
> still be wrong while not necessarily being negative, yes?  In which
> case we'll still display incorrect output?

Here we split exec_vm into main code segment and libraries.

Range start_code .. end_code declared as main code segment.
In my case it's bigger than exec_vm, so libraries have to be negative.

After my patch libraries will be 0 and whole exec_vm show as VmExe.
At least sum VmExe + VmLib stays correct and both of them sane.