linux-kernel - Re: [PATCH v4 00/24] ILP32 for ARM64

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Date:	Wed, 15 Apr 2015 16:49:33 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	"Dr. Philipp Tomsich" <philipp.tomsich@...obroma-systems.com>
Cc:	Andreas Kraschitzer <andreas.kraschitzer@...obroma-systems.com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Andrew Pinski <apinski@...ium.com>,
	Kumar Sankaran <ksankaran@....com>,
	Benedikt Huber <benedikt.huber@...obroma-systems.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Christoph Muellner <christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH v4 00/24] ILP32 for ARM64

On Wed, Apr 15, 2015 at 01:50:51PM +0200, Dr. Philipp Tomsich wrote:
> On 15 Apr 2015, at 13:22, Catalin Marinas <catalin.marinas@....com> wrote:
> > I think you are right. I was more thinking of those routed directly to
> > the native (non-compat) syscalls. We would need to make sure the return
> > value (X0 being the only register not restored on return from exception)
> > has the top 32-bit part zeroed.
> 
> As the kernel is LP64 and will thus attempt to return a 64bit return value, the
> high bits should be properly sign-extended in all cases.
> 
> The problem (posed by procedure call standard) of information leakage could 
> manifest itself only, if the kernel tried to return something smaller than 64 bits… 
> in that case, we can the problem would already exhibit for the LP64 ABI. 
> 
> For the ILP32 implementation, I’ll thus assume that all LP64 ABI calls reused
> are clean in this regard.

Yes. All the compat_sys_* are defined to return a long, so even if ILP32
user space treats it as 32-bit, there is no information leak because of
the kernel's sign-extension. So just a false alarm, we can consider this
part sorted.

-- 
Catalin
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