Re: rng padlock changes causes NetBSD to crash

[Andrius V <vezhlys%gmail.com@localhost>]

Hi,

I have tested the fix.  lcr4(rcr4() | CR4_OSFXSR); helps indeed and
system boots but if statement seems to be not correct, at least on
VT-310DP board it ended up in the same error.

On Wed, Feb 15, 2017 at 6:35 PM, Thor Lancelot Simon <tls%panix.com@localhost> wrote:
> On Wed, Feb 15, 2017 at 10:25:36AM +0200, Andrius V wrote:
>>
>> Crash looks like this:
>>
>> cpu_rng: VIA
>> fatal privileged instruction fault in supervisor mode
>> trap type 0 code 0 eip c0132377 cs 8 eflags 10046 cr2 0 ilevel 8 esp 80050033
>> curlwp 0xc12427e0 pid 0 lid 1 lowest kstack 0xc14d82c0
>> kernel: supervisor trap privileged instruction fault, code=0
>> Stopped in pid 0.1 (system) at netbsd:cpu_rng+0x4a: xstore-rng.
>
> Jonathan Kollasch found the bug: cpu_rng is called before the FPU
> detection code, which would normally enable SSE.  SSE must be enabled
> the PadLock instructions to actually work, regardless of what the MSR
> values say.
>
> Can you test the following patch, before I commit it?
>
>
> Index: identcpu.c
> ===================================================================
> RCS file: /cvsroot/src/sys/arch/x86/x86/identcpu.c,v
> retrieving revision 1.52
> diff -u -p -r1.52 identcpu.c
> --- identcpu.c  2 Feb 2017 08:57:04 -0000       1.52
> +++ identcpu.c  15 Feb 2017 16:32:15 -0000
> @@ -551,7 +551,20 @@ cpu_probe_c3(struct cpu_info *ci)
>                         }
>                     }
>
> -                   /* Actually do the enables. */
> +                   /*
> +                    * Actually do the enables.  It's a little gross,
> +                    * but per the PadLock programming guide, "Enabling
> +                    * PadLock", condition 3, we must enable SSE too or
> +                    * else the first use of RNG or ACE instructions
> +                    * will generate a trap.
> +                    *
> +                    * We must do this early because of kernel RNG
> +                    * initialization but it is safe without the full
> +                    * FPU-detect as all these CPUs have SSE.
> +                    */
> +                   if (cpu_feature[0] & CPUID_FXSR)
> +                       lcr4(rcr4() | CR4_OSFXSR);
> +
>                     if (rng_enable) {
>                         msr = rdmsr(MSR_VIA_RNG);
>                         msr |= MSR_VIA_RNG_ENABLE;