From: WANG Xuerui <git@xxxxxxxxxx> Hi, The LoongArch-64 base architecture is capable of performing bounds-checking either before memory accesses or alone, with specialized instructions generating BCEs (bounds-checking error) in case of failed assertions (ISA manual Volume 1, Sections 2.2.6.1 [1] and 2.2.10.3 [2]). This could be useful for managed runtimes, but the exception is not being handled so far, resulting in SIGSYSes in these cases, which is incorrect and warrants a fix in itself. During experimentation, it was discovered that there is already UAPI for expressing such semantics: SIGSEGV with si_code=SEGV_BNDERR. This was originally added for Intel MPX, and there is currently no user (!) after the removal of MPX support a few years ago. Although the semantics is not a 1:1 match to that of LoongArch, still it is better than alternatives such as SIGTRAP or SIGBUS of BUS_OBJERR kind, due to being able to convey both the value that failed assertion and the bound value. This patch series implements just this approach: translating BCEs into SIGSEGVs with si_code=SEGV_BNDERR, si_value set to the offending value, and si_lower and si_upper set to resemble a range with both lower and upper bound while in fact there is only one. The instructions are not currently used anywhere yet in the fledgling LoongArch ecosystem, so it's not very urgent and we could take the time to figure out the best way forward (should SEGV_BNDERR turn out not suitable). [1]: https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#bound-check-memory-access-instructions [2]: https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#_asrtlegt_d Changes since v1: - rebased on top of current loongarch-next - removed code related to the kprobe notifier mechanism WANG Xuerui (2): LoongArch: Add opcodes of bounds-checking instructions LoongArch: Relay BCE exceptions to userland as SIGSEGVs with si_code=SEGV_BNDERR arch/loongarch/include/asm/inst.h | 26 ++++++++ arch/loongarch/kernel/genex.S | 1 + arch/loongarch/kernel/traps.c | 99 +++++++++++++++++++++++++++++++ 3 files changed, 126 insertions(+) -- 2.40.0
