linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!?

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: <201201260209.54513.vda.linux@googlemail.com>
Date:	Thu, 26 Jan 2012 02:09:54 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	"Indan Zupancic" <indan@....nu>
Cc:	"Oleg Nesterov" <oleg@...hat.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andi Kleen" <andi@...stfloor.org>,
	"Jamie Lokier" <jamie@...reable.org>,
	"Andrew Lutomirski" <luto@....edu>,
	"Will Drewry" <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	ak@...ux.intel.com, eric.dumazet@...il.com, gregkh@...e.de,
	dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com,
	"Roland McGrath" <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On Thursday 26 January 2012 01:40, Indan Zupancic wrote:
> >> We can add the new events,
> >>
> >> 	PTRACE_EVENT_SYSCALL_ENTRY
> >> 	PTRACE_EVENT_SYSCALL_COMPAT_ENTRY
> >> 	PTRACE_EVENT_SYSCALL_EXIT
> >> 	PTRACE_EVENT_SYSCALL_COMPAT_EXIT
> >
> > We can get away with just the first one.
> > (1) It's unlikely people would want to get native sysentry events but not compat ones,
> > thus first two options can be combined into one;
> 
> True.
> 
> > (2) syscall exit compat-ness is known from entry type - no need to indicate it; and
> > (3) if we would flag syscall entry with an event value in wait status, then syscall
> > exit will be already distinquisable.
> 
> False for execve which messes everything up by changing TID sometimes.

Dealt with in Linus tree already: set PTRACE_O_TRACEEXEC option,
and use PTRACE_GETEVENTMSG in PTRACE_EVENT_EXEC stop to get
the old TID.


> > To future-proof this scheme we may reserve a few more event values
> > PTRACE_EVENT_SYSCALL_ENTRY2, PTRACE_EVENT_SYSCALL_ENTRY3, etc,
> > if we'll ever have arches with more than one non-native syscall
> > entry. I'm no expert, but looking at strace code, ARM may already have
> > more than one additional convention how to pass syscall args.
> 
> Please, no! This way lays madness, just one PTRACE_EVENT_SYSCALL_ENTRY,
> no PTRACE_EVENT_SYSCALL_ENTRY1 or PTRACE_EVENT_SYSCALL_ENTRY2, that
> would be horrible. Keep arch specific stuff in arch specific areas,
> please don't spread it around.

The situation when an architecture has 32- and 64-bit varieties,
and sometimes different ABIs (parameter passing comventions),
is rather typical, it's not a quirk of just one unfortunate
architecture.

Please look at strace source, get_scno() function, where
it reads syscall no and parameters. Let's see....
- POWERPC: has 32-bit and 64-bit mode
- X86_64: has 32-bit and 64-bit mode
- IA64: has i386-compat mode
- ARM: has more than one ABI
- SPARC: has 32-bit and 64-bit mode

Do you want to re-invent a different arch-specific way to report
syscall type for each of these arches?


> What was wrong with using eflags again? Is it too simple or something?

It's x86-specific, and abuses a bit in a real register.

-- 
vda
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/