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: <ZVTvvJTOV777UGsP@arm.com>
Date:   Wed, 15 Nov 2023 16:20:12 +0000
From:   "Szabolcs.Nagy@....com" <Szabolcs.Nagy@....com>
To:     Mark Brown <broonie@...nel.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "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>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "vschneid@...hat.com" <vschneid@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "bristot@...hat.com" <bristot@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "Pandey, Sunil K" <sunil.k.pandey@...el.com>
Subject: Re: [PATCH RFC RFT v2 2/5] fork: Add shadow stack support to clone3()

The 11/15/2023 12:36, Mark Brown wrote:
> On Wed, Nov 15, 2023 at 12:45:45AM +0000, Edgecombe, Rick P wrote:
> > On Tue, 2023-11-14 at 20:05 +0000, Mark Brown wrote:
>
> > > +               if (size < 8)
> > > +                       return (unsigned long)ERR_PTR(-EINVAL);
>
> > What is the intention here? The check in map_shadow_stack is to leave
> > space for the token, but here there is no token.
>
> It was to ensure that there is sufficient space for at least one entry
> on the stack.

end marker token (0) needs it i guess.

otherwise 0 size would be fine: the child may not execute
a call instruction at all.

> > I think for CLONE_VM we should not require a non-zero size. Speaking of
> > CLONE_VM we should probably be clear on what the expected behavior is
> > for situations when a new shadow stack is not usually allocated.
> > !CLONE_VM || CLONE_VFORK will use the existing shadow stack. Should we
> > require shadow_stack_size be zero in this case, or just ignore it? I'd
> > lean towards requiring it to be zero so userspace doesn't pass garbage
> > in that we have to accommodate later. What we could possibly need to do
> > around that though, I'm not sure. What do you think?
>
> Yes, requiring it to be zero in that case makes sense I think.

i think the condition is "no specified separate stack for
the child (stack==0 || stack==sp)".

CLONE_VFORK does not imply that the existing stack will be
used (a stack for the child can be specified, i think both
glibc and musl do this in posix_spawn).

IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.