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From: David Laight <David.Laight@ACULAB.COM>
To: "'Madhavan T. Venkataraman'" <madvenka@linux.microsoft.com>,
	"'Mark Rutland'" <mark.rutland@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Linux API <linux-api@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	linux-integrity <linux-integrity@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"LSM List" <linux-security-module@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>, X86 ML <x86@kernel.org>
Subject: RE: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor
Date: Mon, 3 Aug 2020 16:57:47 +0000
Message-ID: <f87f84e466a041fbabd2bba84f4592a5@AcuMS.aculab.com> (raw)
In-Reply-To: <7fdc102e-75ea-6d91-d2a3-7fe8c91802ce@linux.microsoft.com>

From: Madhavan T. Venkataraman
> Sent: 03 August 2020 17:03
> 
> On 8/3/20 3:27 AM, David Laight wrote:
> > 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.
> 
> Is that true only for 32-bit systems only? I thought RIP-relative addressing was
> introduced in 64-bit mode. Please confirm.

I said i386 not amd64 or x86-64.

So yes, 64bit code has PC-relative addressing.
But I'm pretty sure it has no other way to get the PC itself
except using call - certainly nothing in the 'usual' instructions.

	David

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

  reply index

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <aefc85852ea518982e74b233e11e16d2e707bc32>
2020-07-28 13:10 ` madvenka
2020-07-28 13:10   ` [PATCH v1 1/4] [RFC] fs/trampfd: Implement the trampoline file descriptor API madvenka
2020-07-28 14:50     ` Oleg Nesterov
2020-07-28 14:58       ` Madhavan T. Venkataraman
2020-07-28 16:06         ` Oleg Nesterov
2020-07-28 13:10   ` [PATCH v1 2/4] [RFC] x86/trampfd: Provide support for the trampoline file descriptor madvenka
2020-07-30  9:06     ` Greg KH
2020-07-30 14:25       ` Madhavan T. Venkataraman
2020-07-28 13:10   ` [PATCH v1 3/4] [RFC] arm64/trampfd: " madvenka
2020-07-28 13:10   ` [PATCH v1 4/4] [RFC] arm/trampfd: " madvenka
2020-07-28 15:13   ` [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor David Laight
2020-07-28 16:32     ` Madhavan T. Venkataraman
2020-07-28 17:16       ` Andy Lutomirski
2020-07-28 18:52         ` Madhavan T. Venkataraman
2020-07-29  8:36           ` David Laight
2020-07-29 17:55             ` Madhavan T. Venkataraman
     [not found]         ` <81d744c0-923e-35ad-6063-8b186f6a153c@linux.microsoft.com>
2020-07-29  5:16           ` Andy Lutomirski
2020-07-28 16:05   ` Casey Schaufler
2020-07-28 16:49     ` Madhavan T. Venkataraman
2020-07-28 17:05     ` James Morris
2020-07-28 17:08       ` Madhavan T. Venkataraman
2020-07-28 17:31   ` Andy Lutomirski
2020-07-28 19:01     ` Madhavan T. Venkataraman
2020-07-29 13:29     ` Florian Weimer
2020-07-30 13:09     ` David Laight
2020-08-02 11:56       ` Pavel Machek
2020-08-03  8:08         ` David Laight
2020-08-03 15:57           ` Madhavan T. Venkataraman
2020-07-30 14:42     ` Madhavan T. Venkataraman
     [not found]     ` <6540b4b7-3f70-adbf-c922-43886599713a@linux.microsoft.com>
2020-07-30 20:54       ` Andy Lutomirski
2020-07-31 17:13         ` Madhavan T. Venkataraman
2020-07-31 18:31           ` Mark Rutland
2020-08-03  8:27             ` David Laight
2020-08-03 16:03               ` Madhavan T. Venkataraman
2020-08-03 16:57                 ` David Laight [this message]
2020-08-03 17:00                   ` Madhavan T. Venkataraman
2020-08-03 17:58             ` Madhavan T. Venkataraman
2020-08-04 13:55               ` Mark Rutland
2020-08-04 14:33                 ` David Laight
2020-08-04 14:44                   ` David Laight
2020-08-04 14:48                   ` Madhavan T. Venkataraman
2020-08-04 15:46                 ` Madhavan T. Venkataraman
2020-08-02 13:57           ` Florian Weimer
2020-08-02 18:54     ` Madhavan T. Venkataraman
2020-08-02 20:00       ` Andy Lutomirski
2020-08-02 22:58         ` Madhavan T. Venkataraman
2020-08-03 18:36         ` Madhavan T. Venkataraman
2020-08-10 17:34         ` Madhavan T. Venkataraman
2020-08-11 21:12           ` Madhavan T. Venkataraman
2020-08-03  8:23       ` David Laight
2020-08-03 15:59         ` Madhavan T. Venkataraman
2020-07-31 18:09   ` Mark Rutland
2020-07-31 20:08     ` Madhavan T. Venkataraman
2020-08-03 16:57     ` Madhavan T. Venkataraman
2020-08-04 14:30       ` Mark Rutland
2020-08-06 17:26         ` Madhavan T. Venkataraman
2020-08-08 22:17           ` Pavel Machek
2020-08-11 12:41             ` Madhavan T. Venkataraman
2020-08-11 13:08               ` Pavel Machek
2020-08-11 15:54                 ` Madhavan T. Venkataraman
2020-08-12 10:06           ` Mark Rutland
2020-08-12 18:47             ` Madhavan T. Venkataraman
2020-08-19 18:53             ` Mickaël Salaün
2020-09-01 15:42               ` Mark Rutland

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