Date: Mon, 22 Jul 2019 14:03:26 +0200 (CEST) From: Ronald Klop <ronald-lists@klop.ws> To: Laurie Jennings <laurie_jennings_1977@yahoo.com> Cc: FreeBSD Current <freebsd-current@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com> Subject: Re: mmap port from 9 not working Message-ID: <1027101659.12.1563797006919@localhost> In-Reply-To: <550659871.4389820.1563721133104@mail.yahoo.com> References: <446145008.4396329.1563680883838.ref@mail.yahoo.com> <446145008.4396329.1563680883838@mail.yahoo.com> <20190721144404.GJ47193@kib.kiev.ua> <550659871.4389820.1563721133104@mail.yahoo.com>
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Van: Laurie Jennings <laurie_jennings_1977@yahoo.com>
Datum: zondag, 21 juli 2019 16:58
Aan: Konstantin Belousov <kostikbel@gmail.com>
CC: FreeBSD Current <freebsd-current@freebsd.org>
Onderwerp: Re: mmap port from 9 not working
>
> On Sunday, July 21, 2019, 10:44:14 AM EDT, Konstantin Belousov <kostikbel@gmail.com> wrote:
>
> On Sun, Jul 21, 2019 at 03:48:03AM +0000, Laurie Jennings wrote:
> > I have some custom stuff I'm porting from Freebsd 9.x using mmap. I get a pointer from the kernel via an ioctl and I map it into a shared buffer.
> > char *kptr; // mem ptr from kernel
> > fd=open("/dev/kmem",O_RDWR);memp=mmap(0,size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,(off_t) ptr);
> >
> > This worked perfectly in 9; memp I had a shared block of memory between the kernel and user space.
> > In 11.3 this returns an errno 22, which is pretty murky. I did notice that off_t doesnt yield an actual offset; I've tried putting in the correct value manuallybut it just fails and fails.I've tried read only also.
> > Please Help!
>
> | Start with providing (and looking yourself) at the output of kdump/ktrace
> | around the failing mmap. The checks for correctness of the mmap(2) arguments
> | were greatly improved during years after FreeBSD 9.
> Since posting this I found a thread that said something about mmap no longer supporting /dev/kmem. If that's that case I need to find another method. No sense spending a day debugging something thatisn't supposed to work.
> SHOULD this still work? This always worked fine with non-wired memory but maybe things have changed since 9.
>
It looks like this is not possible anymore. Here is the code change with some explanation.
https://svnweb.freebsd.org/base?view=revision&revision=307332
https://reviews.freebsd.org/D8248
Just a question of my site out of interest to people who know more about this than I do. Does Page Table Isolation (PTI) also prevent mapping /dev/kmem in user space?
https://wiki.freebsd.org/SpeculativeExecutionVulnerabilities#Meltdown_.28CVE-2017-5754.29
Regards,
Ronald.
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Date: Mon, 22 Jul 2019 15:12:09 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Ronald Klop <ronald-lists@klop.ws>
Cc: Laurie Jennings <laurie_jennings_1977@yahoo.com>,
FreeBSD Current <freebsd-current@freebsd.org>
Subject: Re: mmap port from 9 not working
Message-ID: <20190722121209.GL47193@kib.kiev.ua>
References: <446145008.4396329.1563680883838.ref@mail.yahoo.com>
<446145008.4396329.1563680883838@mail.yahoo.com>
<20190721144404.GJ47193@kib.kiev.ua>
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On Mon, Jul 22, 2019 at 02:03:26PM +0200, Ronald Klop wrote:
>
> Van: Laurie Jennings <laurie_jennings_1977@yahoo.com>
> Datum: zondag, 21 juli 2019 16:58
> Aan: Konstantin Belousov <kostikbel@gmail.com>
> CC: FreeBSD Current <freebsd-current@freebsd.org>
> Onderwerp: Re: mmap port from 9 not working
> >
> > On Sunday, July 21, 2019, 10:44:14 AM EDT, Konstantin Belousov <kostikbel@gmail.com> wrote:
> >
> > On Sun, Jul 21, 2019 at 03:48:03AM +0000, Laurie Jennings wrote:
> > > I have some custom stuff I'm porting from Freebsd 9.x using mmap. I get a pointer from the kernel via an ioctl and I map it into a shared buffer.
> > > char *kptr; // mem ptr from kernel
> > > fd=open("/dev/kmem",O_RDWR);memp=mmap(0,size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,(off_t) ptr);
> > >
> > > This worked perfectly in 9; memp I had a shared block of memory between the kernel and user space.
> > > In 11.3 this returns an errno 22, which is pretty murky. I did notice that off_t doesnt yield an actual offset; I've tried putting in the correct value manuallybut it just fails and fails.I've tried read only also.
> > > Please Help!
> >
> > | Start with providing (and looking yourself) at the output of kdump/ktrace
> > | around the failing mmap. The checks for correctness of the mmap(2) arguments
> > | were greatly improved during years after FreeBSD 9.
> > Since posting this I found a thread that said something about mmap no longer supporting /dev/kmem. If that's that case I need to find another method. No sense spending a day debugging something thatisn't supposed to work.
> > SHOULD this still work? This always worked fine with non-wired memory but maybe things have changed since 9.
> >
> It looks like this is not possible anymore. Here is the code change with some explanation.
> https://svnweb.freebsd.org/base?view=revision&revision=307332
> https://reviews.freebsd.org/D8248
>
> Just a question of my site out of interest to people who know more about this than I do. Does Page Table Isolation (PTI) also prevent mapping /dev/kmem in user space?
> https://wiki.freebsd.org/SpeculativeExecutionVulnerabilities#Meltdown_.28CVE-2017-5754.29
KPTI has nothing to do with that.
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