Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

Steven Rostedt
2020-04-07T21:48:29Z

On Tue, 07 Apr 2020 13:02:40 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> Since we now have infrastructure to analyze module text, disallow
> modules that write to CRn and DRn registers.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/x86/kernel/module.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -266,6 +266,22 @@ static bool insn_is_vmx(struct insn *ins
> return false;
> }
>
> +static bool insn_is_mov_CRn(struct insn *insn)
> +{
> + if (insn->opcode.bytes[0] == 0x0f && insn->opcode.bytes[1] == 0x22)
> + return true;
> +
> + return false;
> +}
> +
> +static bool insn_is_mov_DRn(struct insn *insn)
> +{
> + if (insn->opcode.bytes[0] == 0x0f && insn->opcode.bytes[1] == 0x23)
> + return true;
> +
> + return false;
> +}
> +
> static int decode_module(struct module *mod, void *text, void *text_end, bool sld_safe)
> {
> bool allow_vmx = sld_safe || !split_lock_enabled();
> @@ -285,6 +301,11 @@ static int decode_module(struct module *
> return -ENOEXEC;
> }
>
> + if (insn_is_mov_CRn(&insn) || insn_is_mov_DRn(&insn)) {
> + pr_err("Module writes to CRn or DRn, please use the proper accessors: %s\n", mod->name);
> + return -ENOEXEC;
> + }

Hmm, wont this break jailhouse?

-- Steve

> +
> text += insn.length;
> }
>
>