On Fri Dec 1, 2023 at 3:00 AM CST, Alexander Lakhin wrote:
[ this thread separated from [1] as the discussion focus shifted ]H Andres, 29.11.2023 22:39, Andres Freund wrote: >> I use the following: >> ASAN_OPTIONS=detect_leaks=0:abort_on_error=1:print_stacktrace=1:\ >> disable_coredump=0:strict_string_checks=1:check_initialization_order=1:\ >> strict_init_order=1:detect_stack_use_after_return=0 > I wonder if we should add some of these options by default ourselves. We could > e.g. add something like the __ubsan_default_options() in > src/backend/main/main.c to src/port/... instead, and return a combination of > "our" options (like detect_leaks=0) and the ones from the environment. I think that such explicit expression of the project policy regarding sanitizer checks is for good, but I see some obstacles on this way. First, I'm not sure what to do with new useful options/maybe new option values, that will appear in sanitizers eventually. Should the only options, that are supported by all sanitizers' versions, be specified, or we may expect that unsupported options/values would be ignored by old versions? Second, what to do with other binaries, that need detect_leaks=0, for example, that same ecpg? > ISTM that, if it actually works as I theorize it should, using > __attribute__((no_sanitize("address"))) would be the easiest approach > here. Something like > > #if defined(__has_feature) && __has_feature(address_sanitizer) > #define pg_attribute_no_asan __attribute__((no_sanitize("address"))) > #else > #define pg_attribute_no_asan > #endif > > or such should work. I've tried adding: bool +__attribute__((no_sanitize("address"))) stack_is_too_deep(void) and it does work got me with clang 15, 18: `make check-world` passes with ASAN_OPTIONS=detect_leaks=0:abort_on_error=1:print_stacktrace=1:\ disable_coredump=0:strict_string_checks=1:check_initialization_order=1:\ strict_init_order=1:detect_stack_use_after_return=1 UBSAN_OPTIONS=abort_on_error=1:print_stacktrace=1 (with a fix for pg_bsd_indent applied [2]) But with gcc 11, 12, 13 I get an assertion failure during `make check`: #4 0x00007fabadcd67f3 in __GI_abort () at ./stdlib/abort.c:79#5 0x0000557f35260382 in ExceptionalCondition (conditionName=0x557f35ca51a0 "(uintptr_t) buffer == TYPEALIGN(PG_IO_ALIGN_SIZE, buffer)", fileName=0x557f35ca4fc0 "md.c", lineNumber=471) at assert.c:66 #6 0x0000557f34a3b2bc in mdextend (reln=0x6250000375c8, forknum=MAIN_FORKNUM, blocknum=18, buffer=0x7fabaa800020, skipFsync=true) at md.c:471 #7 0x0000557f34a45a6f in smgrextend (reln=0x6250000375c8, forknum=MAIN_FORKNUM, blocknum=18, buffer=0x7fabaa800020, skipFsync=true) at smgr.c:501 #8 0x0000557f349139ed in RelationCopyStorageUsingBuffer (srclocator=..., dstlocator=..., forkNum=MAIN_FORKNUM, permanent=true) at bufmgr.c:4386The buffer (buf) declared as follows: static void RelationCopyStorageUsingBuffer(RelFileLocator srclocator, RelFileLocator dstlocator, ForkNumber forkNum, bool permanent) { ... PGIOAlignedBlock buf; ... But as we can see, the buffer address is really not 4k-aligned, and that offset 0x20 added in run-time only when the server started with detect_stack_use_after_return=1. So it looks like the asan feature detect_stack_use_after_return implemented in gcc allows itself to add some data on stack, that breaks our alignment expectations. With all three such Asserts in md.c removed, `make check-world` passes for me.
Decided to do some digging into this, and Google actually documents[0] how it works. After reading the algorithm, it is obvious why this fails. What happens if you throw an __attribute__((no_sanitize("address")) on the function? I assume the Asserts would then pass. The commit[1] which added pg_attribute_aligned() provides insight as to why the Asserts exist.
/* If this build supports direct I/O, the buffer must be I/O aligned. */
Disabling instrumentation in functions which use this specific type when the build supports direct IO seems like the best solution.
> One thing that's been holding me back on trying to do something around this is > the basically non-existing documentation around all of this. I haven't even > found documentation referencing the fact that there are headers like > sanitizer/asan_interface.h, you just have to figure that out yourself. Compare > that to something like valgrind, which has documented this at least somewhat. Yes, so maybe it's reasonable to support only basic/common features (such as detect_leaks), leaving advanced ones for ad-hoc usage till they prove their worthiness.
Possibly, but I think I would rather see upstream support running with all features with instrumentation turned off in various sections of code. Even some assistance from AddressSanitizer is better than none. Here[1][2] are all the AddressSanitizer flags for those curious.
Best regards, Alexander [1] https://www.postgresql.org/message-id/flat/CWTLB2WWVJJ2.2YV6ERNOL1WVF%40neon.tech [2] https://www.postgresql.org/message-id/591971ce-25c1-90f3-0526-5f54e3ebb32e%40gmail.com
I personally would like to see Postgres have support for AddressSanitizer. I think it already supports UndefinedBehaviorSanitizer if I am remembering the buildfarm properly. AddressSanitizer has been so helpful in past experiences writing C.
[0]: https://github.com/google/sanitizers/wiki/AddressSanitizerUseAfterReturn#algorithm [1]: https://github.com/postgres/postgres/commit/faeedbcefd40bfdf314e048c425b6d9208896d90 [2]: https://github.com/google/sanitizers/wiki/AddressSanitizerFlags [3]: https://github.com/google/sanitizers/wiki/SanitizerCommonFlags -- Tristan Partin Neon (https://neon.tech)
