RE: [PATCH] arm64: Add config to limit user space to 47bits

From: Zheng Xu <Zheng.Xu@arm.com>
To: "agraf@suse.de" <agraf@suse.de>, Steve Capper <Steve.Capper@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Mark Rutland <Mark.Rutland@arm.com>,
	"mbrugger@suse.com" <mbrugger@suse.com>,
	"Catalin Marinas" <Catalin.Marinas@arm.com>,
	Will Deacon <Will.Deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	Stuart Monteith <Stuart.Monteith@arm.com>
Subject: RE: [PATCH] arm64: Add config to limit user space to 47bits
Date: Thu, 14 Jul 2016 07:49:14 +0000	[thread overview]
Message-ID: <VI1PR0801MB142315FBEDD571CC23E8D7F796320@VI1PR0801MB1423.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <e24481b9-fb6a-aead-a72b-43b7d561b940@suse.de>

Sorry, I might misunderstand the issue. I thought there are still issues with master.

I saw that you've mentioned there are pointers to .rodata. And I only fixed the heap. So I am just worried if there can be issues with .rodata. If pointers to .rodata are not tagged and used as js objects, it should be fine.

Thanks,
Zheng

-----Original Message-----
From: Alexander Graf [mailto:agraf@suse.de]
Sent: 14 July 2016 15:14
To: Zheng Xu; Steve Capper
Cc: Ard Biesheuvel; Mark Rutland; mbrugger@suse.com; Catalin Marinas; Will Deacon; linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; Stuart Monteith
Subject: Re: [PATCH] arm64: Add config to limit user space to 47bits

On 14.07.16 09:03, Zheng Xu wrote:
> LuaJIT also fix the 48VA issue by allocating heap memory below 47 bits.
>
> For mozjs issue, if there are pointers to .rodata, it can be a problem. Does it happen on master and do we have any case to reproduce the issue so that I can take a look?

mozjs is fixed with your patch. I backported it to all of the ancient versions of mozjs, so we're probably good there. Though every distro will have to redo that work in their own trees, because older versions of mozjs are no longer maintained upstream. If you want to be a hero, you can try to port polkitd and gnome to use more recent versions of mozjs ;). Or maybe they can already and we just messed up packaging.

The issue I mentioned with "js 1.8.5" is this gem:

https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Releases/1.8.5

I don't know the exact history, but I think it predates mozjs. With a bit of sledge hammering your heap allocation patch applies there too, but we still get the rodata references.

Alex

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