Date: Tue, 18 Dec 2018 10:57:26 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Brooks Davis <brooks@freebsd.org> Cc: Kurt Lidl <lidl@pix.net>, freebsd-stable@freebsd.org Subject: Re: Address Collision using i386 4G/4G Memory Split Message-ID: <20181218085726.GD60291@kib.kiev.ua> In-Reply-To: <20181218083425.GA20811@spindle.one-eyed-alien.net> References: <38ad0d50-c776-9deb-d56b-db8db548cefc@tu-dortmund.de> <064a6212-40df-2dad-32fb-4cade922c65d@pix.net> <20181218083425.GA20811@spindle.one-eyed-alien.net>
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On Tue, Dec 18, 2018 at 08:34:25AM +0000, Brooks Davis wrote: > On Mon, Dec 17, 2018 at 03:58:05PM -0500, Kurt Lidl wrote: > > Alexander Lochmann writes: > > > According to git commit e3089a (https://reviews.freebsd.org/D1463) > > > FreeBSD 12.0 i386 uses separate address spaces for kernel and user > > > space. So basically two memory areas, one in each space, can have the > > > same address. > > > Is this possible with FreeBSD 12.0? Is this likely to happen? > > > > If the userspace program and the kernel address happen to overlap, the > > system will deal with it. There's not anything to worry about. As to > > whether or not it's likely to happen -- I'm not sure about that. I > > expect the default stack and heap space locations for a fresh process > > have changed due to this change, but it should not matter. > > 4/4 does potentially alter the failure modes of buggy code that tries to > read directly from userspace addresses. For example, correct calls to > the sysctls fixed in r342125 may panic prior to the fix because the > addresses in question aren't mapped in kernel space. They might also > fail or behave bizarrely if the page is mapped and the value from the > kernel page is used. I believe that SMAP on amd64 is The solution to find such cases, now. And it indeed catched several real cases, e.g. pci(4), acpi_call and vbox from ports, besides the mentioned commit..
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