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Sender: Arvind Sankar <niveditas98@gmail.com>
From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Wed, 23 Sep 2020 14:49:30 -0400
To:     Solar Designer <solar@openwall.com>
Cc:     Florian Weimer <fweimer@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        madvenka@linux.microsoft.com, kernel-hardening@lists.openwall.com,
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        Rich Felker <dalias@libc.org>
Subject: Re: [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor
Message-ID: <20200923184930.GA1352963@rani.riverdale.lan>
References: <20200922215326.4603-1-madvenka@linux.microsoft.com>
 <20200923081426.GA30279@amd>
 <20200923091456.GA6177@openwall.com>
 <87wo0ko8v0.fsf@oldenburg2.str.redhat.com>
 <20200923181136.GA8846@openwall.com>
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On Wed, Sep 23, 2020 at 08:11:36PM +0200, Solar Designer wrote:
> On Wed, Sep 23, 2020 at 04:39:31PM +0200, Florian Weimer wrote:
> > * Solar Designer:
> > 
> > > While I share my opinion here, I don't mean that to block Madhavan's
> > > work.  I'd rather defer to people more knowledgeable in current userland
> > > and ABI issues/limitations and plans on dealing with those, especially
> > > to Florian Weimer.  I haven't seen Florian say anything specific for or
> > > against Madhavan's proposal, and I'd like to.  (Have I missed that?)
> 
> [...]
> > I think it's unnecessary for the libffi use case.
> [...]
> 
> > I don't know if kernel support could
> > make sense in this context, but it would be a completely different
> > patch.
> 
> Thanks.  Are there currently relevant use cases where the proposed
> trampfd would be useful and likely actually made use of by userland -
> e.g., specific userland project developers saying they'd use it, or
> Madhavan intending to develop and contribute userland patches?
> 
> Alexander

The trampoline it provides in this version can be implemented completely
in userspace. The kernel part of it is essentially just providing a way
to do text relocations without needing a WX mapping, but the text
relocations would be unnecessary in the first place if the trampoline
was position-independent code.