linux-kernel - Re: [PATCH PTI v3 10/10] x86/pti: Put the LDT in its own PGD if PTI is on

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Date:   Sat, 16 Dec 2017 01:39:45 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH PTI v3 10/10] x86/pti: Put the LDT in its own PGD if PTI
 is on

On Tue, 12 Dec 2017, Andy Lutomirski wrote:
> +
> +	return 0;
> +#else
> +	return -EINVAL;

Errm. What's the point of that? Breaking non PTI?

>  	new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
>  	if (!new_ldt) {
> @@ -155,8 +266,17 @@ int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
>  	memcpy(new_ldt->entries, old_mm->context.ldt->entries,
>  	       new_ldt->nr_entries * LDT_ENTRY_SIZE);
>  	finalize_ldt_struct(new_ldt);
> +	retval = map_ldt_struct(mm, new_ldt, 0);
> +	if (retval)
> +		goto out_free;
>  
>  	mm->context.ldt = new_ldt;
> +	goto out_unlock;
> +
> +out_free:
> +	free_ldt_pgtables(mm);
> +	free_ldt_struct(new_ldt);
> +	return retval;

Leaks old_mm->context_lock;

Thanks,

	tglx