[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20110712132449.GB11336@aftab>
Date: Tue, 12 Jul 2011 15:24:49 +0200
From: Borislav Petkov <bp@...64.org>
To: Andrew Lutomirski <luto@....edu>
Cc: Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...e.hu>, John Stultz <johnstul@...ibm.com>,
Borislav Petkov <bp@...64.org>
Subject: Re: [PATCH v2 1/8] x86-64: Improve vsyscall emulation CS and RIP
handling
On Tue, Jul 12, 2011 at 08:58:58AM -0400, Andrew Lutomirski wrote:
> On Tue, Jul 12, 2011 at 3:18 AM, Borislav Petkov <bp@...en8.de> wrote:
> > On Mon, Jul 11, 2011 at 06:20:50PM -0400, Andrew Lutomirski wrote:
> >> > I'm wondering: why don't you make this function return negative value on
> >> > error, i.e. -EINVAL and the vsyscall number on success so that you can
> >> > get rid of returning it through the arg pointer?
> >> >
> >> > Then at the callsite you can do:
> >> >
> >> > vsyscall_nr = addr_to_vsyscall_nr(addr);
> >> > if (vsyscall_nr < 0)
> >> > warn_bad_vsyscall(...)
> >>
> >> Because I don't want a warning about ret being used without being initialized.
> >
> > not if you preinit it...
>
> I kind of like that warning as a sanity check, and preiniting it
> grates against my irrational desire to over-optimize :)
:-)
> >
> >> With the code in this patch, the compiler is smart enough to figure
> >> out that either vsyscall_nr is 0, 1, or 2 or that the EINVAL branch is
> >> taken. I'll see if it works the other way.
> >
> > here's what i mean, I changed your patch a bit:
>
> How about this:
>
> static int addr_to_vsyscall_nr(unsigned long addr)
> {
> int nr;
>
> if ((addr & ~0xC00UL) != VSYSCALL_START)
> return -EINVAL;
>
> nr = (addr & 0xC00UL) >> 10;
> if (nr >= 3)
> return -EINVAL;
>
> return nr;
> }
>
> ...
>
> int vsyscall_nr;
>
> ...
>
> vsyscall_nr = addr_to_vsyscall_nr(regs->ip - 2);
> if (vsyscall_nr < 0) {
> warn_bad_vsyscall(KERN_WARNING, regs,
> "illegal int 0xcc (exploit attempt?)");
> goto sigsegv;
> }
>
> gcc 4.6 at least does not warn.
Yep, looks good.
> Also, IRQ disabling was still mismatched in the sigsegv path. I'll
> fix that as well.
oh yeah.
Thanks.
--
Regards/Gruss,
Boris.
Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
HRB Nr. 43632 WEEE Registernr: 129 19551
--
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/
Powered by blists - more mailing lists