Re: [RESEND PATCH v2 4/4] x86/umip: Warn if UMIP-protected instructions are used

[Ingo Molnar]

* Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx> wrote:

> +const char * const umip_insns[5] = {
> +	[UMIP_INST_SGDT] = "sgdt",
> +	[UMIP_INST_SIDT] = "sidt",
> +	[UMIP_INST_SMSW] = "smsw",
> +	[UMIP_INST_SLDT] = "sldt",
> +	[UMIP_INST_STR] = "str",
> +};

Sigh ...

> +/*
> + * If you change these strings, ensure that buffers using them are sufficiently
> + * large.
> + */
> +static const char umip_warn_use[] = "cannot be used by applications.";
> +static const char umip_warn_emu[] = "For now, expensive software emulation returns result.";

Please use the string literals directly, don't add an extra obfuscation layer.

Plus:

> +	unsigned char buf[MAX_INSN_SIZE], warn[128];

> +	snprintf(warn, sizeof(warn), "%s %s", umip_insns[umip_inst],
> +		 umip_warn_use);

This is incredibly fragile against future buffer overflows, and warning about it 
in comments does not make it less fragile!

Thanks,

	Ingo