On 03/06/2017 05:24 PM, Dmitry Vyukov wrote: > Let me provide more context and design alternatives. > > There are also other archs, at least arm64 for now. > There are also other tools. For KTSAN (race detector) we will > absolutely need to hook into atomic ops. For KMSAN (uses of unit > values) we also need to understand atomic ops at least to some degree. > Both of them will require different instrumentation. > For KASAN we are also more interested in cases where it's more likely > that an object is touched only by an asm, but not by normal memory > accesses (otherwise we would report the bug on the normal access, > which is fine, this makes atomic ops stand out in my opinion). > > We could involve compiler (and by compiler I mean clang, because we > are not going to touch gcc, any volunteers?). We've tried this with gcc about 3 years ago. Here is the patch - https://gcc.gnu.org/ml/gcc-patches/2014-05/msg02447.html The problem is that memory block in "m" constraint doesn't actually mean that inline asm will access it. It only means that asm block *may* access that memory (or part of it). This causes false positives. As I vaguely remember I hit some false-positive in FPU-related code. This problem gave birth to another idea - add a new constraint to strictly mark the memory access inside asm block. See https://gcc.gnu.org/ml/gcc/2014-09/msg00237.html But all ended with nothing. > However, it's unclear if it will be simpler or not. There will > definitely will be a problem with uaccess asm blocks. Currently KASAN > relies of the fact that it does not see uaccess accesses and the user > addresses are considered bad by KASAN. There can also be a problem > with offsets/sizes, it's not possible to figure out what exactly an > asm block touches, we can only assume that it directly dereferences > the passed pointer. However, for example, bitops touch the pointer > with offset. Looking at the current x86 impl, we should be able to > handle it because the offset is computed outside of asm blocks. But > it's unclear if we hit this problem in other places. > > I also see that arm64 bitops are implemented in .S files. And we won't > be able to instrument them in compiler. > There can also be other problems. Is it possible that some asm blocks > accept e.g. physical addresses? KASAN would consider them as bad. > -- 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>
