linux-kernel - Re: [PATCH] [v3] xen: remove pre-xen3 fallback handlers

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Date:   Wed, 14 Mar 2018 18:47:13 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Arnd Bergmann <arnd@...db.de>, Juergen Gross <jgross@...e.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        David Woodhouse <dwmw@...zon.co.uk>,
        Stefano Stabellini <sstabellini@...nel.org>,
        linux-kernel@...r.kernel.org, Jan Beulich <jbeulich@...e.com>
Subject: Re: [PATCH] [v3] xen: remove pre-xen3 fallback handlers

On 03/13/2018 05:06 PM, Arnd Bergmann wrote:
> The legacy hypercall handlers were originally added with
> a comment explaining that "copying the argument structures in
> HYPERVISOR_event_channel_op() and HYPERVISOR_physdev_op() into the local
> variable is sufficiently safe" and only made sure to not write
> past the end of the argument structure, the checks in linux/string.h
> disagree with that, when link-time optimizations are used:
>
> In function 'memcpy',
>     inlined from 'pirq_query_unmask' at drivers/xen/fallback.c:53:2,
>     inlined from '__startup_pirq' at drivers/xen/events/events_base.c:529:2,
>     inlined from 'restore_pirqs' at drivers/xen/events/events_base.c:1439:3,
>     inlined from 'xen_irq_resume' at drivers/xen/events/events_base.c:1581:2:
> include/linux/string.h:350:3: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter
>    __read_overflow2();
>    ^
>
> Further research turned out that only Xen 3.0.2 or earlier required the
> fallback at all, while all versions in use today don't need it.
> As far as I can tell, it is not even possible to run a mainline kernel
> on those old Xen releases, at the time when they were in use, only
> a patched kernel was supported anyway.
>
> Fixes: cf47a83fb06e ("xen/hypercall: fix hypercall fallback code for very old hypervisors")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> [v2] use a table lookup instead of a switch/case statement, after
> multiple suggestions.
> [v3] remove that file completely

(+Jan who added this file originally)

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>