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Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing a privcmd call

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On Fri, Sep 11, 2015 at 06:36:05PM +0100, Julien Grall wrote:
> On 11/09/15 18:32, Julien Grall wrote:
> > On 11/09/15 18:00, Russell King - ARM Linux wrote:
> >> On Fri, Sep 11, 2015 at 05:25:59PM +0100, Julien Grall wrote:
> >>> +	/*
> >>> +	 * Privcmd calls are issued by the userspace. We need to allow the
> >>> +	 * kernel to access the userspace memory before issuing the hypercall.
> >>> +	 */
> >>> +	uaccess_enable r4
> >>> +
> >>> +	/* r4 is loaded now as we use it as scratch register before */
> >>>  	ldr r4, [sp, #4]
> >>
> >> As I mentioned in one of my previous mails, "ip" should be safe to use
> >> here - it's a caller-corrupted register, just like r0-r3 and lr.  So,
> >> you could do:
> >>
> >> 	ldr r4, [sp, #4]
> >> +	uaccess_enable ip
> > 
> > The register ip (aka r12) is used to store the hypercall number. So we
> > can't reuse it as scratch register.
> > 
> > The easiest one is r4.
> > 
> >>
> >> which fractionally tightens the window.
> >>
> >> However, there's nothing actually wrong with your version - there's no
> >> way we could've got this far with sp pointing at userspace.
> >>
> >> I'm happy with either version, so:
> >>
> >> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
> >>
> >> How do you want to handle the patch?  I already have some other uaccess
> >> fixes queued up to send to Linus before the merge window closes.
> 
> Forgot to answer to this bits. I was thinking to ask Stefano carrying
> the patch in xentip. Although it won't go until rc1.
> 
> I don't mind if it's going earlier in Linux/master.

Thanks, I've applied your patch as-is now.

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[PATCH v2] arm/xen: Enable user access to the kernel before issuing a privcmd call Julien Grall <julien.grall@citrix.com> - 2015-09-11 18:50 +0200
  Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-11 19:10 +0200
    Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing  a privcmd call Julien Grall <julien.grall@citrix.com> - 2015-09-11 19:40 +0200
      Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing  a privcmd call Julien Grall <julien.grall@citrix.com> - 2015-09-11 19:40 +0200
        Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-11 20:00 +0200
          Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-09-11 20:00 +0200
            Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-11 20:10 +0200
              Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-09-14 11:40 +0200
                Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-14 12:10 +0200
                Re: [PATCH v2] arm/xen: Enable user access to the kernel before  issuing a privcmd call Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-09-14 13:20 +0200
    Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing  a privcmd call Julien Grall <julien.grall@citrix.com> - 2015-09-11 20:00 +0200

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