On Thu, 5 Jan 2023 16:29:13 GMT, Justin King <jck...@openjdk.org> wrote:
>> This change instruments Metaspace for ASan. Metaspace allocates memory using >> `mmap`/`munmap` which ASan is not aware of. Fortunately ASan supports >> applications [manually poisoning/unpoisoning >> memory](https://github.com/google/sanitizers/wiki/AddressSanitizerManualPoisoning). >> ASan is able to detect poisoned memory, similar to `use-after-free`, and >> will raise an error similarly called `use-after-poison`. This provides and >> extra layer of defense and confidence. >> >> The header `sanitizers/address.h` defines macros for poisoning/unpoisoning >> memory regions. These macros can be used regardless of build mode. When ASan >> is not available, they are implemented using a NOOP approach which still >> compiles the arguments but does so such that they will be stripped out by >> the compiler due to being unreachable. This helps with maintenance. >> >> This also has the added benefit of making >> [LSan](https://bugs.openjdk.org/browse/JDK-8298445) more accurate and >> deterministic, as LSan will not look for pointers to malloc memory in >> poisoned memory regions. >> >> IMO the benefit of doing this greatly outweighs the cost. > > Justin King has updated the pull request incrementally with one additional > commit since the last revision: > > Use -fno-common as suggested by ASan docs > > Signed-off-by: Justin King <jck...@google.com> Yeah, I was originally going for the most pedantic implementation. But I like your proposed approach and it strikes a happy middle ground. > That explains (I think) another question I had. Which is how are overlapped > ranges handled. Given four subsequent addresses a b c d, I should be able to > poison [b,c) and then poison [a,d), right? Or do I have to take care to only > pass non-overlapping mappings? ASAN is fine with overlapping. It doesn't check the current state of poisoning/unpoisoning when doing the operations. Though there are variants that do such as __sanitizer_annotate_contiguous_container, but that is for instrumenting contiguous containers similar to std::vector. That will come at a later time for applicable Hotspot containers, but out of scope for this change and unrelated to Metaspace. > Great. I'll take a look next week since I still have vacation. No problem. ------------- PR: https://git.openjdk.org/jdk/pull/11702
