linux-kernel - Re: [PATCH v33 15/21] x86/vdso: Add support for exception fixup in vDSO functions

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]

Date:   Tue, 30 Jun 2020 09:48:22 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, linux-sgx@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asapek@...gle.com, "Xing, Cedric" <cedric.xing@...el.com>,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, Dave Hansen <dave.hansen@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, kmoy@...gle.com,
        Christian Ludloff <ludloff@...gle.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Neil Horman <nhorman@...hat.com>, npmccallum@...hat.com,
        puiterwijk@...hat.com, David Rientjes <rientjes@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, yaozhangx@...gle.com
Subject: Re: [PATCH v33 15/21] x86/vdso: Add support for exception fixup in
 vDSO functions

On Tue, Jun 30, 2020 at 1:41 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Mon, Jun 29, 2020 at 11:00:55PM -0700, Sean Christopherson wrote:
> > E.g. the vDSO function should get the fixup even if userspace screws
> > up mmap() and invokes __vdso_sgx_enter_enclave() without being tagged
> > an SGX task.
>
> I sincerely hope you don't mean this seriously.
>
> Please add a member to task_struct which denotes that a task is an
> sgx task, test that member where needed and forget real quickly about
> running *any* *fixup* for unrelated tasks.

I don't see the problem.  If you call this magic vDSO function and get
a fault, it gets handled.  What's the failure mode?

>
> > No hard dependency, it's normal kernel code.  My reasoning for dropping it
> > in .../vdso was largely to co-locate it with vdso/extable.h due to the
> > dependency on the format of 'struct vdso_exception_table_entry'.
>
> A struct which you defined instead of simply using struct
> exception_table_entry even if it has a handler member which would remain
> unused?

Don't forget the cross-arch issue.  We need that structure to have
constant layout so that the -m32 build from the vDSO has the same
layout as in the kernel.

So my only actual objection to the patch is that there should probably
be a comment above the structure reminding people that it needs to
have the same layout on 32-bit, x32, and x86_64.  So maybe the entries
should be s32 instead of int, although this doesn't really matter.