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Date: Tue, 25 Jun 2019 13:13:11 -0700
From: Andy Lutomirski <>
To: Kees Cook <>
Cc: Florian Weimer <>, Linux API <>, 
	Kernel Hardening <>,, 
	linux-arch <>, Andy Lutomirski <>, 
	"Carlos O'Donell" <>
Subject: Re: Detecting the availability of VSYSCALL

On Tue, Jun 25, 2019 at 1:08 PM Kees Cook <> wrote:
> On Tue, Jun 25, 2019 at 05:15:27PM +0200, Florian Weimer wrote:
> > Should we try mapping something at the magic address (without MAP_FIXED)
> > and see if we get back a different address?  Something in the auxiliary
> > vector would work for us, too, but nothing seems to exists there
> > unfortunately.
> It seems like mmap() won't even work because it's in the high memory
> area. I can't map something a page under the vsyscall page either, so I
> can't distinguish it with mmap, mprotect, madvise, or msync. :(

I keep contemplating making munmap() work on it.  That would nicely
answer the question: if munmap() fails, it's not there, and, if
munmap() succeeds, it's not there :)

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