linux-kernel - Re: [RFC v3 PATCH 5/5] x86: check VM

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Message-ID: <20180702124558.GP19043@dhcp22.suse.cz>
Date:   Mon, 2 Jul 2018 14:45:58 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, willy@...radead.org,
        akpm@...ux-foundation.org, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, tglx@...utronix.de,
        hpa@...or.com, linux-mm@...ck.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v3 PATCH 5/5] x86: check VM_DEAD flag in page fault

On Mon 02-07-18 14:26:09, Laurent Dufour wrote:
> On 02/07/2018 14:15, Michal Hocko wrote:
> > On Mon 02-07-18 10:45:03, Laurent Dufour wrote:
> >> On 30/06/2018 00:39, Yang Shi wrote:
> >>> Check VM_DEAD flag of vma in page fault handler, if it is set, trigger
> >>> SIGSEGV.
> >>>
> >>> Cc: Michal Hocko <mhocko@...nel.org>
> >>> Cc: Thomas Gleixner <tglx@...utronix.de>
> >>> Cc: Ingo Molnar <mingo@...hat.com>
> >>> Cc: "H. Peter Anvin" <hpa@...or.com>
> >>> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> >>> ---
> >>>  arch/x86/mm/fault.c | 4 ++++
> >>>  1 file changed, 4 insertions(+)
> >>>
> >>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> >>> index 9a84a0d..3fd2da5 100644
> >>> --- a/arch/x86/mm/fault.c
> >>> +++ b/arch/x86/mm/fault.c
> >>> @@ -1357,6 +1357,10 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs)
> >>>  		bad_area(regs, error_code, address);
> >>>  		return;
> >>>  	}
> >>> +	if (unlikely(vma->vm_flags & VM_DEAD)) {
> >>> +		bad_area(regs, error_code, address);
> >>> +		return;
> >>> +	}
> >>
> >> This will have to be done for all the supported architectures, what about doing
> >> this check in handle_mm_fault() and return VM_FAULT_SIGSEGV ?
> > 
> > We already do have a model for that. Have a look at MMF_UNSTABLE.
> 
> MMF_UNSTABLE is a mm's flag, here this is a VMA's flag which is checked.

Yeah, and we have the VMA ready for all places where we do check the
flag. check_stable_address_space can be made to get vma rather than mm.

-- 
Michal Hocko
SUSE Labs