On 3/9/20 10:00 AM, Yu-cheng Yu wrote: > On Wed, 2020-02-26 at 09:57 -0800, Dave Hansen wrote: >>> index ade4e6ec23e0..8b69ebf0baed 100644 >>> --- a/Documentation/admin-guide/kernel-parameters.txt >>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>> @@ -3001,6 +3001,12 @@ >>> noexec=on: enable non-executable mappings (default) >>> noexec=off: disable non-executable mappings >>> >>> + no_cet_shstk [X86-64] Disable Shadow Stack for user-mode >>> + applications >> >> If we ever add kernel support, "no_cet_shstk" will mean "no cet shstk >> for userspace"? > > What about no_user_shstk, no_kernel_shstk? Those are better. >>> + no_cet_ibt [X86-64] Disable Indirect Branch Tracking for user-mode >>> + applications >>> + >>> nosmap [X86,PPC] >>> Disable SMAP (Supervisor Mode Access Prevention) >>> even if it is supported by processor. >> >> BTW, this documentation is misplaced. It needs to go to the spot where >> you introduce the code for these options. > > We used to introduce the document later in the series. The feedback was to > introduce it first so that readers know what to expect. To me, that doesn't apply for things that are implemented in this specific of a spot in the code and *ALSO* might not even make the final series. >>> +Note: >>> + There is no CET-enabling arch_prctl function. By design, CET is >>> + enabled automatically if the binary and the system can support it. >> >> This is kinda interesting. It means that a JIT couldn't choose to >> protect the code it generates and have different rules from itself? > > JIT needs to be updated for CET first. Once that is done, it runs with CET > enabled. It can use the NOTRACK prefix, for example. Am I missing something? What's the direct connection between shadow stacks and Indirect Branch Tracking other than Intel marketing umbrellas? >>> + The parameters passed are always unsigned 64-bit. When an IA32 >>> + application passing pointers, it should only use the lower 32 bits. >> >> Won't a 32-bit app calling prctl() use the 32-bit ABI? How would it >> even know it's running on a 64-bit kernel? > > The 32-bit app is passing only a pointer to an array of 64-bit numbers. Well, the documentation just talked about pointers and I naively assume it means the "unsigned long *" you had in there. Rather than make suggestions, just say that the ABI is universally 64-bit. Saying that the pointers must be valid is just kinda silly. It's also not 100% clear what an "IA32 application" *MEANS* given fun things like x32. Also, I went to go find this implementation in your series. I couldn't find it. Did I miss a patch? Or are you documenting things you didn't even implement?
