Messages in this thread |  | | Date | Tue, 12 Jul 2011 15:24:49 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2 1/8] x86-64: Improve vsyscall emulation CS and RIP handling |
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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@alien8.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.
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