linux-kernel - Re: x86: mm: Fix vmalloc_fault oops during lazy MMU updates.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130221123306.GA6781@phenom.dumpdata.com>
Date:	Thu, 21 Feb 2013 07:33:06 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Samu Kallio <samu.kallio@...rdeencloud.com>, mingo@...hat.com,
	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: x86: mm: Fix vmalloc_fault oops during lazy MMU updates.

On Sun, Feb 17, 2013 at 02:35:52AM -0000, Samu Kallio wrote:
> In paravirtualized x86_64 kernels, vmalloc_fault may cause an oops
> when lazy MMU updates are enabled, because set_pgd effects are being
> deferred.
> 
> One instance of this problem is during process mm cleanup with memory
> cgroups enabled. The chain of events is as follows:
> 
> - zap_pte_range enables lazy MMU updates
> - zap_pte_range eventually calls mem_cgroup_charge_statistics,
>   which accesses the vmalloc'd mem_cgroup per-cpu stat area
> - vmalloc_fault is triggered which tries to sync the corresponding
>   PGD entry with set_pgd, but the update is deferred
> - vmalloc_fault oopses due to a mismatch in the PUD entries
> 
> Calling arch_flush_lazy_mmu_mode immediately after set_pgd makes the
> changes visible to the consistency checks.

How do you reproduce this? Is there a BUG() or WARN() trace that
is triggered when this happens?

Also pls next time also CC me.
> 
> Signed-off-by: Samu Kallio <samu.kallio@...rdeencloud.com>
> 
> ---
> arch/x86/mm/fault.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8e13ecb..0a45298 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -378,10 +378,12 @@ static noinline __kprobes int vmalloc_fault(unsigned long address)
>  	if (pgd_none(*pgd_ref))
>  		return -1;
>  
> -	if (pgd_none(*pgd))
> +	if (pgd_none(*pgd)) {
>  		set_pgd(pgd, *pgd_ref);
> -	else
> +		arch_flush_lazy_mmu_mode();
> +	} else {
>  		BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
> +	}
>  
>  	/*
>  	 * Below here mismatches are bugs because these lower tables
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/