On Mon, Dec 12, 2016 at 2:43 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > On Mon, Dec 12, 2016 at 12:12 PM, Vaneet Narang <v.narang@xxxxxxxxxxx> wrote: >> >> Hi, >> >> >>> Do you actually hit an issue with image size? In what context? >> >>> Do you use inline/outline instrumentation? Does switching to the other >> >>> option help? >> >> >> >> Memory access with KASAN enabled Image has overhead in terms of cpu execution. >> >> Sometimes we are not able to reproduce race condition issues with these overhead in >> >> place. So user should have control atleast over read instrumentation. >> > >> >Don't you want to disable KASAN entirely in such case? >> >> hmmm, but we need KASAN to detect corruption issues so overhead can be >> reduced by switching OFF read instrumentation. Generally Reads are much more frequent >> than writes as latest arm64 kernel has 224000 reads and 62300 writes >> which is almost 3.5 times. So i think this control is required. >> >> >> >>> Does it make sense to ever disable writes? I assume that you are >> >> >> >> Write instrumentation control is majorly kept to be inline with ASAN for user space >> >> applications. >> >> Also write is sometimes useful when uImage is already sanitized and some corruption >> >> is done by kernel modules by doing some direct memory access then both read / write sanity of uImage >> >> can be avoided. >> > >> >But then you don't need KASAN at all. >> >> KASAN support is required in this case to detect module issues. >> KASAN provides asan_load / asan_store definition as these functions >> are added by compiler in modules before every memory access. >> These are the functions which will do address sanity and detect errors. > [resending as plain text] Ah, OK, I see. So you want to e.g. not instrument kernel (for both reads and writes), but instrument a single module. That makes sense. Please extend the Usage section of KASAN docs: https://kernel.org/doc/html/latest/dev-tools/kasan.html#usage mention not instrumenting writes for whole kernel, and instrumenting a single module. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
