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