Date: Tue, 18 Dec 2018 08:34:25 +0000 From: Brooks Davis <brooks@freebsd.org> To: Kurt Lidl <lidl@pix.net> Cc: freebsd-stable@freebsd.org Subject: Re: Address Collision using i386 4G/4G Memory Split Message-ID: <20181218083425.GA20811@spindle.one-eyed-alien.net> In-Reply-To: <064a6212-40df-2dad-32fb-4cade922c65d@pix.net> References: <38ad0d50-c776-9deb-d56b-db8db548cefc@tu-dortmund.de> <064a6212-40df-2dad-32fb-4cade922c65d@pix.net>
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--rwEMma7ioTxnRzrJ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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? >=20 > If the userspace program and the kernel address happen to overlap, the=20 > 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. -- Brooks --rwEMma7ioTxnRzrJ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAEBAgAGBQJcGLERAAoJEKzQXbSebgfAqN4H/1yXiglpEIFNTJ033cpdthEk fFORpvHlJoC67PZ86//mvSJ0/MbB0MuCualwFW8HV4Hj9KA7579R2f+aYFcjUxaz 9vmXnwtgLPZRKEXcQp+mTX/DQYBzVvNXY2Qfxq21D9k65XYCsomlBT812PQyl22p mkxZTCLma1bKfr0MAJdmx2RpPhftGm8FQZKdVDhcoZ3AN0a7LdnyeRAO6xb00t8P NexWaIybeb3cLavuVGF6tbb38a5jFTIdklU5j46PtrXAt6n8bpNURHnIpeNQFHYF fias0aIZKqSm1z3wok/OIrCe2CAKwEU/v6FKpobFKgqPqjprCdPu86dUWunqGLw= =BLPX -----END PGP SIGNATURE----- --rwEMma7ioTxnRzrJ--
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