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]

Date:   Mon, 3 Aug 2020 08:27:25 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mark Rutland' <mark.rutland@....com>,
        "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
CC:     Andy Lutomirski <luto@...nel.org>,
        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

From: Mark Rutland
> Sent: 31 July 2020 19:32
...
> > It requires PC-relative data references. I have not worked on all architectures.
> > So, I need to study this. But do all ISAs support PC-relative data references?
> 
> Not all do, but pretty much any recent ISA will as it's a practical
> necessity for fast position-independent code.

i386 has neither PC-relative addressing nor moves from %pc.
The cpu architecture knows that the sequence:
	call	1f  
1:	pop	%reg  
is used to get the %pc value so is treated specially so that
it doesn't 'trash' the return stack.

So PIC code isn't too bad, but you have to use the correct
sequence.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)