Re: [PATCHv2] ARM32: Support mremap() for sigpage/vDSO

[Russell King - ARM Linux]

On Thu, May 18, 2017 at 02:13:29PM +0300, Dmitry Safonov wrote:
> On 04/25/2017 08:18 PM, Dmitry Safonov wrote:
> >On 04/14/2017 04:25 PM, Dmitry Safonov wrote:
> >>CRIU restores application mappings on the same place where they
> >>were before Checkpoint. That means, that we need to move vDSO
> >>and sigpage during restore on exactly the same place where
> >>they were before C/R.
> >>
> >>Make mremap() code update mm->context.{sigpage,vdso} pointers
> >>during VMA move. Sigpage is used for landing after handling
> >>a signal - if the pointer is not updated during moving, the
> >>application might crash on any signal after mremap().
> >>
> >>vDSO pointer on ARM32 is used only for setting auxv at this moment,
> >>update it during mremap() in case of future usage.
> >>
> >>Without those updates, current work of CRIU on ARM32 is not reliable.
> >>Historically, we error Checkpointing if we find vDSO page on ARM32
> >>and suggest user to disable CONFIG_VDSO.
> >>But that's not correct - it goes from x86 where signal processing
> >>is ended in vDSO blob. For arm32 it's sigpage, which is not disabled
> >>with `CONFIG_VDSO=n'.
> >>
> >>Looks like C/R was working by luck - because userspace on ARM32 at
> >>this moment always sets SA_RESTORER.
> >>
> >>Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> >>Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> >>Cc: Will Deacon <will.deacon@xxxxxxx>
> >>Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> >>Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >>Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> >>Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> >>Cc: Christopher Covington <cov@xxxxxxxxxxxxxx>
> >>Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> >>---
> >>v2: (buildbot) Fix (unsinged long) to (void*) cast warning.
> >>
> >>  arch/arm/kernel/process.c |  8 ++++++++
> >>  arch/arm/kernel/vdso.c    | 18 ++++++++++++++++++
> >>  arch/x86/entry/vdso/vma.c |  3 ---
> >>  mm/mmap.c                 |  4 ++++
> >>  4 files changed, 30 insertions(+), 3 deletions(-)
> >
> >Ping?
> 
> Ping?

I'm mostly happy with the ARM bits, but I can't take the patch without
acks from others because it touches other architectures/generic code.

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