[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] arm/xen: Enable user access to the kernel before issuing a privcmd call
On 11/09/15 16:25, Russell King - ARM Linux wrote: > On Fri, Sep 11, 2015 at 03:56:38PM +0100, Julien Grall wrote: >> Well, we can't assume that the function will be called with uaccess >> disabled. > > Please explain your reasoning. I think I was confused about the usage of uaccess. Thank you for the explanation. > The reason copy_from_user() et.al. need to save and restore the DACR is > because the DACR may be in one of two states on older ARM architectures. > It may have set the kernel domain to 'manager' mode, to allow these > accessors to work on kernel memory, or the kernel domain may be in > 'client' mode, thereby preventing the accessors from touching kernel > memory. > > Unless the code path is reachable with the kernel domain in manager > mode, (iow, a set_fs(KERNEL_DS) or set_fs(get_ds()) has been done) then > it should be safe to use uaccess_disable/uaccess_enable. I believe that our privcmd driver doesn't made any usage of set_fs(...), so I will use the uaccess_{disable,enable} macro. Regards, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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