On Thu, Feb 02, 2023 at 11:49:42AM -0800, Sami Tolvanen wrote: > On Thu, Feb 2, 2023 at 11:31 AM Nick Desaulniers > <ndesaulniers@xxxxxxxxxx> wrote: > > > > On Thu, Feb 2, 2023 at 11:20 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > > > On Thu, 2 Feb 2023 at 20:10, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > > > > > > On Thu, Feb 02, 2023 at 10:56:29AM -0800, John Stultz wrote: > > > > > That said, making sense of the error message isn't completely trivial > > > > > either. I've been seeing a few cases recently of some of the new > > > > > compiler tooling (I pinged you earlier on a CFI one) causing errors > > > > > that developers aren't really sure how to address. I know sometimes > > > > > it's not easy to surface the errors with context to what was wrong, > > > > > but at the risk of intense bike shedding, is there some way to provide > > > > > something like "Likely array bounds error" instead of just "BRK > > > > > handler: Fatal exception"? > > > > > > > > Yeah, this is a result of the size trade-off that resulted in config > > > > CONFIG_UBSAN_TRAP -- there ends up being no message about what went > > > > wrong. I'd really like to have cleaner handling of this -- perhaps what > > > > was done for KCFI could be applied to UBSAN as well, though this is an > > > > area I don't know well myself. (i.e. encoding "this was a UBSAN trap" > > > > in the trap itself.) > > > > > > > > Sami or Ard, is this something that could be improved for arm64? > > > > > > > > > > -ENOCONTEXT, so I am going to assume this is about runtime > > > instrumentation that needs some kind of 'panic' function which it will > > > invoke if some condition is met that should never occur? > > > > > > We already use brk with different immediate values in the opcode, so > > > the arch layer already has what we need. Is this a limitation in the > > > compiler, perhaps, where it always emits the same brk opcode? > > > > Yeah, we'd need to update both the compiler to produce the encoding, > > and the kernel to recognize the encoding and do something special. > > A quick look at Clang's source code suggests that Intrinsic::ubsantrap > already accepts the handler ID (from the SanitizerHandler enum) as an > argument and the arm64 LLVM back-end appears to encode the value as an > immediate for the brk instruction. I didn't confirm that this actually > works, but perhaps we just need to teach the kernel about the possible > values? Oh excellent. Yeah, if that's all that's needed here that would be great. What are the values? -- Kees Cook
