On Thu, Sep 22, 2016 at 3:22 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Wed, Sep 21, 2016 at 11:58 AM, Kyle Huey <me@xxxxxxxxxxxx> wrote: >> Intel supports faulting on the CPUID instruction beginning with Ivy Bridge. >> When enabled, the processor will fault on attempts to execute the CPUID >> instruction with CPL>0. Exposing this feature to userspace will allow a >> ptracer to trap and emulate the CPUID instruction. >> >> When supported, this feature is controlled by toggling bit 0 of >> MSR_MISC_FEATURES_ENABLES. It is documented in detail in Section 2.3.2 of >> http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf >> > >> + if (!test_and_set_thread_flag(TIF_NOCPUID)) >> + /* >> + * Must flip the CPU state synchronously with >> + * TIF_NOCPUID in the current running context. >> + */ >> + switch_cpuid_faulting(true); > > If statements with multiple indented lines should have braces in my > book. See, for example, "goto fail". > > > static? > >> +int set_cpuid_mode(struct task_struct *task, unsigned long val) > > static? > >> + * Called immediately after a successful exec. >> + */ >> +void arch_post_exec(void) >> +{ >> + /* If cpuid was previously disabled for this task, re-enable it. */ >> + if (test_thread_flag(TIF_NOCPUID)) >> + enable_cpuid(); >> +} > >> diff --git a/fs/exec.c b/fs/exec.c >> index 6fcfb3f..0272b7e 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -1287,6 +1287,7 @@ void setup_new_exec(struct linux_binprm * bprm) >> else >> set_dumpable(current->mm, suid_dumpable); >> >> + arch_post_exec(); > > Let's call this arch_setup_new_exec(). > >> perf_event_exec(); >> __set_task_comm(current, kbasename(bprm->filename), true); >> >> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h >> index 2b5b10e..22a3f61 100644 >> --- a/include/linux/thread_info.h >> +++ b/include/linux/thread_info.h >> @@ -130,6 +130,10 @@ static inline void check_object_size(const void *ptr, unsigned long n, >> { } >> #endif /* CONFIG_HARDENED_USERCOPY */ >> >> +#ifndef arch_post_exec >> +static inline void arch_post_exec(void) {} >> +#endif >> + > > thread_info.h is a weird place for this IMO. Admittedly, elf.h isn't > a whole lot better. Maybe fs.h? - Kyle -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
