On Tue, Feb 13, 2018 at 2:25 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Mon, Feb 12, 2018 at 4:40 PM, Laura Abbott <labbott@xxxxxxxxxx> wrote: >> On 02/12/2018 03:27 PM, Kees Cook wrote: >>> >>> On Sun, Feb 4, 2018 at 7:05 AM, Igor Stoppa <igor.stoppa@xxxxxxxxxx> >>> wrote: >>>> >>>> On 04/02/18 00:29, Boris Lukashev wrote: >>>>> >>>>> On Sat, Feb 3, 2018 at 3:32 PM, Igor Stoppa <igor.stoppa@xxxxxxxxxx> >>>>> wrote: >>>> >>>> >>>> [...] >>>> >>>>>> What you are suggesting, if I have understood it correctly, is that, >>>>>> when the pool is protected, the addresses already given out, will >>>>>> become >>>>>> traps that get resolved through a lookup table that is built based on >>>>>> the content of each allocation. >>>>>> >>>>>> That seems to generate a lot of overhead, not to mention the fact that >>>>>> it might not play very well with the MMU. >>>>> >>>>> >>>>> That is effectively what i'm suggesting - as a form of protection for >>>>> consumers against direct reads of data which may have been corrupted >>>>> by some irrelevant means. In the context of pmalloc, it would probably >>>>> be a separate type of ro+verified pool >>>> >>>> ok, that seems more like an extension though. >>>> >>>> ATM I am having problems gaining traction to get even the basic merged >>>> :-) >>>> >>>> I would consider this as a possibility for future work, unless it is >>>> said that it's necessary for pmalloc to be accepted ... >>> >>> >>> I would agree: let's get basic functionality in first. Both >>> verification and the physmap part can be done separately, IMO. >> >> >> Skipping over physmap leaves a pretty big area of exposure that could >> be difficult to solve later. I appreciate this might block basic >> functionality but I don't think we should just gloss over it without >> at least some idea of what we would do. > > What's our exposure on physmap for other regions? e.g. things that are > executable, or made read-only later (like __ro_after_init)? I just checked on a system with a 4.9 kernel, and there seems to be no physical memory that is mapped as writable in the init PGD and executable elsewhere. Ah, I think I missed something. At least on X86, set_memory_ro, set_memory_rw, set_memory_nx and set_memory_x all use change_page_attr_clear/change_page_attr_set, which use change_page_attr_set_clr, which calls __change_page_attr_set_clr() with a second parameter "checkalias" that is set to 1 unless the bit being changed is the NX bit, and that parameter causes the invocation of cpa_process_alias(), which will, for mapped ranges, also change the attributes of physmap ranges. set_memory_ro() and so on are also used by the module loading code. But in the ARM64 code, I don't see anything similar. Does anyone with a better understanding of ARM64 want to check whether I missed something? Or maybe, with a recent kernel, check whether executable module pages show up with a second writable mapping in the "kernel_page_tables" file in debugfs? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
