On Tue, Aug 05, 2008 at 02:03:24PM +0400, Stanislav Sedov wrote: > On Mon, 16 Jun 2008 14:42:41 -0400 > Coleman Kane <cokane_at_FreeBSD.org> mentioned: > > > > > Is it potentially "unsafe" to use RDMSR? > > > > Well, it might disclose some sensitive information, > as well as create covert channels. E.g. some of the > registers contains kernel thread pointers, etc; some > of them undocumented. It won't be very wise to give > access to the rdmsr feature to all users on a > multi-user machine. > > Sorry for this taking so long. You messages spotted > a bug in my security model for this driver, so I've > redone that. Now, the access to the rdmsr and cpuid > features will be granted only if the caller has > read permissions on the device, and wrmsr/update > - only if he've opened the device for writing. > This way you can provide fine-grained control to > the driver features. > > I've also added the cpucontrol utility which provided > userland accesss to the driver, and allows to apply > microcode updates. > > The latest patch against HEAD is available here: > ftp://ftp.SpringDaemons.com/dustheap/cpuctl.4.diff > > Thanks! --- a/sys/amd64/amd64/support.S +++ b/sys/amd64/amd64/support.S _at__at_ -765,6 +765,7 _at__at_ ENTRY(wrmsr_safe) */ ALIGN_TEXT msr_onfault: - movq $0,PCB_ONFAULT(%r8) - movl $EFAULT,%eax + movq PCPU(CURPCB),%r8 /* set fault handler */ + movq $0,PCB_ONFAULT(%r8) + movq $EFAULT,%rax ret movq $EFAULT,%rax is better to be replaced by movl, %eax. Amd64 specifies automatic zeroing of the upper-half of the registers on the 32bit operation.
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