linux-kernel - Re: [PATCH RFC RFT v2 2/5] fork: Add shadow stack support to clone3()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1bd189e0-a7dd-422c-9766-ef1c9b0d3df8@sirena.org.uk>
Date:   Thu, 16 Nov 2023 12:33:35 +0000
From:   Mark Brown <broonie@...nel.org>
To:     "Szabolcs.Nagy@....com" <Szabolcs.Nagy@....com>
Cc:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "debug@...osinc.com" <debug@...osinc.com>,
        "mgorman@...e.de" <mgorman@...e.de>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "vschneid@...hat.com" <vschneid@...hat.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "bristot@...hat.com" <bristot@...hat.com>,
        "will@...nel.org" <will@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Pandey, Sunil K" <sunil.k.pandey@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>
Subject: Re: [PATCH RFC RFT v2 2/5] fork: Add shadow stack support to clone3()

On Thu, Nov 16, 2023 at 10:32:06AM +0000, Szabolcs.Nagy@....com wrote:
> The 11/16/2023 00:52, Edgecombe, Rick P wrote:
> > On Wed, 2023-11-15 at 18:43 +0000, Mark Brown wrote:

> while CLONE_VFORK allows the child to use the parent shadow
> stack (parent and child cannot execute at the same time and
> the child wont return to frames created by the parent), we
> want to enable precise size accounting of the shadow stack
> so requesting a new shadow stack should work if new stack
> is specified.

> but stack==0 can force shadow_stack_size==0.

> i guess the tricky case is stack!=0 && shadow_stack_size==0:
> the user may want a new shadow stack with default size logic,
> or (with !CLONE_VM || CLONE_VFORK) wants to use the existing
> shadow stack from the parent.

If shadow_stack_size is 0 then we're into clone() behaviour and doing
the default/implicit handling which is to do exactly what the above
describes.

> > What is the case for stack=sp bit of the logic?

> iirc it is not documented in the clone man page what stack=0
> means and of course you don't want sp==0 in the vfork child
> so some targets sets stack to sp in vfork, others set it 0
> and expect the kernel to do the right thing.

The manual page explicitly says that not specifying a stack means to use
the same stack area as the parent.

> this likely does not apply to clone3 where the size has to be
> specified so maybe stack==sp does not need special treatment.

You'd have to be jumping through hoops to manage to get the same stack
pointer while explicitly specifying a stack with clone3() on
architectures where the stack grows down.  I'm not sure there's a
reasonable use case.

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)