linux-kernel - Re: [patch 1/3] x86/ldt: Free the right LDT memory in write

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Message-ID: <20171230213337.tns3dtj7z526bvf2@gmail.com>
Date:   Sat, 30 Dec 2017 22:33:37 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [patch 1/3] x86/ldt: Free the right LDT memory in write_ldt()
 error path


* Thomas Gleixner <tglx@...utronix.de> wrote:

> The error path in write_ldt() frees the already installed LDT memory
> instead of the newly allocated which cannot be installed.

s/newly allocated
 /newly allocated one

> 
> Fixes: f55f0501cbf6 ("x86/pti: Put the LDT in its own PGD if PTI is on")
> Reported-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/kernel/ldt.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/kernel/ldt.c
> +++ b/arch/x86/kernel/ldt.c
> @@ -421,7 +421,7 @@ static int write_ldt(void __user *ptr, u
>  	 */
>  	error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
>  	if (error) {
> -		free_ldt_struct(old_ldt);
> +		free_ldt_struct(new_ldt);
>  		goto out_unlock;
>  	}
>  

This bug kind of scares me ...

Reviewed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo