3 ms·

This is pretty well known technique (tagged pointers themselves go back forever, and using tags for this purpose it's easy to find papers from the 2000's). In f

This is pretty well known technique (tagged pointers themselves go back forever, and using tags for this purpose it's easy to find papers from the 2000's). In fact, it was already being implemented in ASAN on architectures with hardware support :) https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html https://clang.llvm.org/docs/HardwareAssistedAddressSanitizer... Where there is no hardware support, the real world overhead is 35%+ (which this paper finds as well), and you end up with other issues to contend with (you have to de-tag the pointers in a bunch of cases, most kernels don't like them, etc), so software-only approaches have mostly not been bothered with.

zniperr 9y ago
Paper author here, thanks for the interest :). I just wanted to elaborate on the overhead numbers you mentioned. I am not specifically familiar with the 35%+ numbers, but you should take into account the cost of any defense on top of the cost of putting tags in pointers, because that makes all the difference. We found in our experiments on SPEC CPU2006 that, without static analysis for optimizations, the cost of pointer tagging itself (tagging + masking) is 22% geomean, which is almost entirely due to masking on loads/stores. This is with a 64-bit masking constant (0x80000000ffffffff) which is unique to our approach and is relatively inefficient on x86. With 32-bit masking (0xffffffff constant), which is more common, the number is about 14%. This only covers metadata management and is not useful on its own, so you need to implement some kind of defense on top of this which is usually costly. The hardware support used by HWAsan only removes masking overhead by having the (ARM) hardware ignore the upper byte of the pointer, which is a nice way to not having to pay for masking. By the way, source code for Delta Pointers is online since today! https://github.com/vusec/deltapointers https://github.com/vusec/deltapointers
- DannyBee 9y ago
  "I am not specifically familiar with the 35%+ numbers, " This is confusing to me Last sentence of second paragraph of your paper: "We show that Delta Pointers are effective in detecting arbitrary buffer overflows and, at 35% overhead on SPEC, offer much better performance than competing solutions." :) " This only covers metadata management and is not useful on its own, so you need to implement some kind of defense on top of this which is usually costly. The hardware support used by HWAsan only removes masking overhead by having the (ARM) hardware ignore the upper byte of the pointer, which is a nice way to not having to pay for masking." I'm aware :) There are thoughts and plans here.
  - zniperr 9y ago
    Ah, I thought you were referring to HWAsan with the 35%, hence the confusion.

zniperr 9y ago

Paper author here, thanks for the interest :). I just wanted to elaborate on the overhead numbers you mentioned. I am not specifically familiar with the 35%+ numbers, but you should take into account the cost of any defense on top of the cost of putting tags in pointers, because that makes all the difference. We found in our experiments on SPEC CPU2006 that, without static analysis for optimizations, the cost of pointer tagging itself (tagging + masking) is 22% geomean, which is almost entirely due to masking on loads/stores. This is with a 64-bit masking constant (0x80000000ffffffff) which is unique to our approach and is relatively inefficient on x86. With 32-bit masking (0xffffffff constant), which is more common, the number is about 14%. This only covers metadata management and is not useful on its own, so you need to implement some kind of defense on top of this which is usually costly. The hardware support used by HWAsan only removes masking overhead by having the (ARM) hardware ignore the upper byte of the pointer, which is a nice way to not having to pay for masking. By the way, source code for Delta Pointers is online since today! https://github.com/vusec/deltapointers https://github.com/vusec/deltapointers

DannyBee 9y ago
"I am not specifically familiar with the 35%+ numbers, " This is confusing to me Last sentence of second paragraph of your paper: "We show that Delta Pointers are effective in detecting arbitrary buffer overflows and, at 35% overhead on SPEC, offer much better performance than competing solutions." :) " This only covers metadata management and is not useful on its own, so you need to implement some kind of defense on top of this which is usually costly. The hardware support used by HWAsan only removes masking overhead by having the (ARM) hardware ignore the upper byte of the pointer, which is a nice way to not having to pay for masking." I'm aware :) There are thoughts and plans here.
- zniperr 9y ago
  Ah, I thought you were referring to HWAsan with the 35%, hence the confusion.