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Date:   Wed, 23 Jan 2019 09:56:03 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Khalid Aziz <khalid.aziz@oracle.com>
Cc:     juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de,
        ak@linux.intel.com, torvalds@linux-foundation.org,
        liran.alon@oracle.com, keescook@google.com,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
        tyhicks@canonical.com, dwmw@amazon.co.uk,
        andrew.cooper3@citrix.com, jcm@redhat.com,
        boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com,
        joao.m.martins@oracle.com, jmattson@google.com,
        pradeep.vincent@oracle.com, john.haxby@oracle.com,
        tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de,
        steven.sistare@oracle.com, kernel-hardening@lists.openwall.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Tycho Andersen <tycho@docker.com>
Subject: Re: [RFC PATCH v7 07/16] arm64/mm, xpfo: temporarily map dcache
 regions
Message-ID: <20190123145551.GD19289@Konrads-MacBook-Pro.local>
References: <cover.1547153058.git.khalid.aziz@oracle.com>
 <eba179acbfdea5a646c5548cb82138c1c3b74aa2.1547153058.git.khalid.aziz@oracle.com>
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On Thu, Jan 10, 2019 at 02:09:39PM -0700, Khalid Aziz wrote:
> From: Juerg Haefliger <juerg.haefliger@canonical.com>
> 
> If the page is unmapped by XPFO, a data cache flush results in a fatal
> page fault, so let's temporarily map the region, flush the cache, and then
> unmap it.
> 
> v6: actually flush in the face of xpfo, and temporarily map the underlying
>     memory so it can be flushed correctly
> 
> CC: linux-arm-kernel@lists.infradead.org
> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
> Signed-off-by: Tycho Andersen <tycho@docker.com>
> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
> ---
>  arch/arm64/mm/flush.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index 30695a868107..f12f26b60319 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -20,6 +20,7 @@
>  #include <linux/export.h>
>  #include <linux/mm.h>
>  #include <linux/pagemap.h>
> +#include <linux/xpfo.h>
>  
>  #include <asm/cacheflush.h>
>  #include <asm/cache.h>
> @@ -28,9 +29,15 @@
>  void sync_icache_aliases(void *kaddr, unsigned long len)
>  {
>  	unsigned long addr = (unsigned long)kaddr;
> +	unsigned long num_pages = XPFO_NUM_PAGES(addr, len);

Is it possible that the 'len' is more than 32 pages? Or say 1000's
of pages? Which would blow away your stack.

> +	void *mapping[num_pages];
>  
>  	if (icache_is_aliasing()) {
> +		xpfo_temp_map(kaddr, len, mapping,
> +			      sizeof(mapping[0]) * num_pages);
>  		__clean_dcache_area_pou(kaddr, len);
> +		xpfo_temp_unmap(kaddr, len, mapping,
> +			        sizeof(mapping[0]) * num_pages);
>  		__flush_icache_all();
>  	} else {
>  		flush_icache_range(addr, addr + len);
> -- 
> 2.17.1
>