linux-kernel - Re: [PATCH v4 4/5] pagemap: hide physical addresses from non-privileged users

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Message-ID: <20150721081149.GC4490@hori1.linux.bs1.fc.nec.co.jp>
Date:	Tue, 21 Jul 2015 08:11:50 +0000
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Mark Williamson <mwilliamson@...o-software.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v4 4/5] pagemap: hide physical addresses from
 non-privileged users

On Tue, Jul 14, 2015 at 06:37:47PM +0300, Konstantin Khlebnikov wrote:
> This patch makes pagemap readable for normal users and hides physical
> addresses from them. For some use-cases PFN isn't required at all.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Fixes: ab676b7d6fbf ("pagemap: do not leak physical addresses to non-privileged userspace")
> Link: http://lkml.kernel.org/r/1425935472-17949-1-git-send-email-kirill@shutemov.name
> ---
>  fs/proc/task_mmu.c |   25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 040721fa405a..3a5d338ea219 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -937,6 +937,7 @@ typedef struct {
>  struct pagemapread {
>  	int pos, len;		/* units: PM_ENTRY_BYTES, not bytes */
>  	pagemap_entry_t *buffer;
> +	bool show_pfn;
>  };
>  
>  #define PAGEMAP_WALK_SIZE	(PMD_SIZE)
> @@ -1013,7 +1014,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
>  	struct page *page = NULL;
>  
>  	if (pte_present(pte)) {
> -		frame = pte_pfn(pte);
> +		if (pm->show_pfn)
> +			frame = pte_pfn(pte);
>  		flags |= PM_PRESENT;
>  		page = vm_normal_page(vma, addr, pte);
>  		if (pte_soft_dirty(pte))

Don't you need the same if (pm->show_pfn) check in is_swap_pte path, too?
(although I don't think that it can be exploited by row hammer attack ...)

Thanks,
Naoya Horiguchi--
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