Re: [PATCH v2] x86/traps: Enable UBSAN traps on x86

[Kees Cook]

On Sat, Jun 01, 2024 at 03:10:05AM +0000, Gatlin Newhouse wrote:
> +void handle_ubsan_failure(struct pt_regs *regs, int insn)
> +{
> +     u32 type = 0;
> +
> +     if (insn == INSN_ASOP) {
> +             type = (*(u16 *)(regs->ip + LEN_ASOP + LEN_UD1));
> +             if ((type & 0xFF) == 0x40)
> +                     type = (type >> 8) & 0xFF;
> +     } else {
> +             type = (*(u16 *)(regs->ip + LEN_UD1));
> +             if ((type & 0xFF) == 0x40)
> +                     type = (type >> 8) & 0xFF;
> +     }

The if/else code is repeated, but the only difference is the offset to
read from. Also, if the 0x40 is absent, we likely don't want to report
anything. So, perhaps:

        u16 offset = LEN_UD1;
        u32 type;

        if (insn == INSN_ASOP)
                offset += INSN_ASOP;
        type = *(u16 *)(regs->ip + offset);
        if ((type & 0xFF) != 0x40)
                return;

        type = (type >> 8) & 0xFF;
        pr_crit("%s at %pS\n", report_ubsan_failure(regs, type), (void 
*)regs->ip);



-- 
Kees Cook