On Sat, Jan 06, 2018 at 11:49:24AM +0000, David Woodhouse wrote: > +/* > + * NOSPEC_JMP and NOSPEC_CALL macros can be used instead of a simple > + * indirect jmp/call which may be susceptible to the Spectre variant 2 > + * attack. > + */
Can be, or must be? > +.macro NOSPEC_JMP reg:req > +#ifdef CONFIG_RETPOLINE > + ALTERNATIVE_2 __stringify(jmp *\reg), \ > + __stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE, \ > + __stringify(lfence; jmp *\reg), X86_FEATURE_RETPOLINE_AMD > +#else > + jmp *\reg > +#endif > +.endm > + > +.macro NOSPEC_CALL reg:req > +#ifdef CONFIG_RETPOLINE > + ALTERNATIVE_2 __stringify(call *\reg), \ > + __stringify(RETPOLINE_CALL \reg), X86_FEATURE_RETPOLINE,\ > + __stringify(lfence; call *\reg), X86_FEATURE_RETPOLINE_AMD > +#else > + call *\reg > +#endif > +.endm Would it make any sense to name these INDIRECT_JMP and INDIRECT_CALL instead? NOSPEC_ seems to describe how it needs to be implemented on some CPUs, as opposed to what the user wants to do (make an indirect jump or call). Eric
