[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 Fri, Sep 11, 2015 at 03:45:29PM +0100, Julien Grall wrote: > Looking to the uaccess_save macro: > > .macro uaccess_save, tmp > #ifdef CONFIG_CPU_SW_DOMAIN_PAN > mrc p15, 0, \tmp, c3, c0, 0 > str \tmp, [sp, #S_FRAME_SIZE] > #endif > .endm > > > It's saving the register on the Stack with an offset S_FRAME_SIZE. > AFAICT, S_FRAME_SIZE is the size of the pt_regs structure. While in the kernel, the uaccess state will be disabled except for the specific sites reading or writing userspace. That means the user-access part of the DACR is well known. What isn't known is whether we're executing here in the kernel segment (set_fs(get_ds())) or not - which allows the kernel to use the userspace accessors to safely read from its own memory space. If we can assume that's not in effect, then the DACR value is fully known at this point, and you can just do a: uaccess_enable rtmp HVC call uaccess_disable rtmp where rtmp is a register you can afford to be changed by the macro. I suspect 'ip' would be a good choice there. Please put the macros as close to __HVC(XEN_IMM) as possible. Thanks. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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