Messages in this thread | | | Date | Mon, 14 Sep 2015 10:36:55 +0100 | From | Stefano Stabellini <> | Subject | Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing a privcmd call |
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On Fri, 11 Sep 2015, Russell King - ARM Linux wrote: > On Fri, Sep 11, 2015 at 06:56:50PM +0100, Stefano Stabellini wrote: > > On Fri, 11 Sep 2015, Russell King - ARM Linux wrote: > > > 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. > > > > That's fine by me, the patch looks good. > > If you'd like your ack on it, please send one, I can still do that.
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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