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

From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	David Laight <David.Laight@aculab.com>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH PTI v3 10/10] x86/pti: Put the LDT in its own PGD if PTI is on
Date: Sat, 16 Dec 2017 01:39:45 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1712160136460.2099@nanos> (raw)
In-Reply-To: <6e2fc833b964e8dc18af406f3fb86e0fc7fbf736.1513035461.git.luto@kernel.org>

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