linux-kernel - Re: scif_insert

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Message-ID: <20190320102607.GA9457@linux.intel.com>
Date:   Wed, 20 Mar 2019 12:26:07 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sudeep Dutt <sudeep.dutt@...el.com>
Cc:     ashutosh.dixit@...el.com, linux-kernel@...r.kernel.org
Subject: Re: scif_insert_vma()

On Sun, Mar 17, 2019 at 10:47:40PM -0700, Sudeep Dutt wrote:
> On Mon, 2019-03-11 at 08:45 +0200, Jarkko Sakkinen wrote:
> > Hi
> > 
> > Just wondering what will happen if kzalloc() fails in scif_mmap.c. How
> > it is recovered? I don't see anything in the VMA callbacks taking care
> > of this.
> 
> Hi Jarkko,
> 
> scif_insert_vma(..) is called from scif_mmap(..) and scif_vma_open(..).
> scif_mmap(..) checks for allocation failures but scif_vma_open(..) does
> not on purpose.
> 
> The vm_operations_struct open(..)/close(..) callbacks do not allow
> returning errors. The driver will take a reference to the VMA private
> data structure irrespective of whether the allocation during the
> open(..) callback succeeds or fails. The close(..) callback cleans up
> the data structures from the mmap(..) or open(..) callbacks if any.

I'm doing allocations also in SGX vma_open callback and was grepping
through kernel tree for how allocations were handled.  Thanks for
clarifying this. In SGX's case I ended up with allowing to fail in
vma open and doing SIGBUS in the #PF handler if so...

/Jarkko