linux-kernel - Re: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor

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: <20200802115600.GB1162@bug>
Date:   Sun, 2 Aug 2020 13:56:01 +0200
From:   Pavel Machek <pavel@....cz>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Andy Lutomirski' <luto@...nel.org>,
        "madvenka@...ux.microsoft.com" <madvenka@...ux.microsoft.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor

Hi!

> > This is quite clever, but now I???m wondering just how much kernel help
> > is really needed. In your series, the trampoline is an non-executable
> > page.  I can think of at least two alternative approaches, and I'd
> > like to know the pros and cons.
> > 
> > 1. Entirely userspace: a return trampoline would be something like:
> > 
> > 1:
> > pushq %rax
> > pushq %rbc
> > pushq %rcx
> > ...
> > pushq %r15
> > movq %rsp, %rdi # pointer to saved regs
> > leaq 1b(%rip), %rsi # pointer to the trampoline itself
> > callq trampoline_handler # see below
> 
> For nested calls (where the trampoline needs to pass the
> original stack frame to the nested function) I think you
> just need a page full of:
> 	mov	$0, scratch_reg; jmp trampoline_handler

I believe you could do with mov %pc, scratch_reg; jmp ...

That has advantage of being able to share single physical page across multiple virtual pages...


									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html