Date: Thu, 23 Feb 2012 08:12:43 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Ian Lepore <freebsd@damnhippie.dyndns.org>, Ryan Stone <rysto32@gmail.com>, Svetlin Manavski <svetlin.manavski@itrinegy.com> Subject: Re: How to access kernel memory from user space Message-ID: <201202230812.43126.jhb@freebsd.org> In-Reply-To: <CAFMmRNx_f4pPzPKipC_3gORHkbauhi1jqMmOY7z_Pf8kdit_pw@mail.gmail.com> References: <CACRNAiv_huiJuzXHsEKNHdFdnpFuAK7fimjWbVVfmdRth2nVDA@mail.gmail.com> <1329938141.21804.4.camel@revolution.hippie.lan> <CAFMmRNx_f4pPzPKipC_3gORHkbauhi1jqMmOY7z_Pf8kdit_pw@mail.gmail.com>
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On Wednesday, February 22, 2012 8:06:20 pm Ryan Stone wrote: > On Wed, Feb 22, 2012 at 2:15 PM, Ian Lepore > <freebsd@damnhippie.dyndns.org> wrote: > > I've never done this, but if I needed to, I think the first thing I'd > > try is to use an mmap(2) of /dev/kmem to map the memory you need into > > userspace (of course your userspace app will need to be running with > > root privs to do this). > > > > That leaves the interesting problem of locating what offset within the > > kernel virtual address space you need to map to get at your data. Two > > things come to mind... have your kernel module export the address in a > > sysctl (that feels kind of hack-ish but it should be quick and easy to > > do), or use libkvm's kvm_nlist() function to locate the symbol within > > your module (I think that should be possible; again I've never actually > > done any of this). > > A far easier way to do this is to have the module create its own > device in /dev that exports the memory by implementing the mmap > interface in the cdev. Yes. Another option you can do if you want to let userland "donate" a buffer to the kernel is to let userland create a buffer using shm_open() (probably with SHM_ANON) and then use shm_map() in the kernel to map that into KVA. -- John Baldwin
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