Re: [PATCH v3 3/3] x86,arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction

[Kyle Huey]

On Thu, Sep 15, 2016 at 5:07 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Thu, Sep 15, 2016 at 4:33 PM, Kyle Huey <me@xxxxxxxxxxxx> wrote:
>> +int get_cpuid_mode(unsigned long adr)
>> +{
>> +       unsigned int val;
>> +
>> +       if (test_thread_flag(TIF_NOCPUID))
>> +               val = ARCH_CPUID_SIGSEGV;
>> +       else
>> +               val = ARCH_CPUID_ENABLE;
>> +
>> +       return put_user(val, (unsigned int __user *)adr);
>> +}
>
> Can we just do:
>
> if (arg2 != 0)
>   return -EINVAL;
> else
>  return test_thread_flag(TIF_NOCPUID) ? ARCH_CPUID_SIGSEGBV : ARCH_CPUID_ENABLE;

We could.  I copied the pattern of PR_GET_TSC here, but I don't feel
strongly about it.

>> diff --git a/tools/testing/selftests/x86/cpuid-fault.c b/tools/testing/selftests/x86/cpuid-fault.c
>> new file mode 100644
>> index 0000000..a9f3f68
>> --- /dev/null
>> +++ b/tools/testing/selftests/x86/cpuid-fault.c
>> @@ -0,0 +1,234 @@
>> +
>> +/*
>> + * Tests for arch_prctl(ARCH_GET_CPUID, ...) / prctl(ARCH_SET_CPUID, ...)
>> + *
>> + * Basic test to test behaviour of ARCH_GET_CPUID and ARCH_SET_CPUID
>> + */
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <unistd.h>
>> +#include <signal.h>
>> +#include <inttypes.h>
>> +#include <cpuid.h>
>> +#include <errno.h>
>> +#include <sys/wait.h>
>> +
>> +#include <sys/prctl.h>
>> +#include <linux/prctl.h>
>> +
>> +const char *cpuid_names[] = {
>> +       [0] = "[not set]",
>
> Is 0 even possible?

Only if the call fails.

- Kyle