Commit 0b61f2c0 authored Sep 11, 2015 by Julien Grall Committed by Russell King Sep 11, 2015

arm/xen: Enable user access to the kernel before issuing a privcmd call



When Xen is copying data to/from the guest it will check if the kernel
has the right to do the access. If not, the hypercall will return an
error.

After the commit a5e090ac "ARM:
software-based privileged-no-access support", the kernel can't access
any longer the user space by default. This will result to fail on every
hypercall made by the userspace (i.e via privcmd).

We have to enable the userspace access and then restore the correct
permission every time the privcmd is used to made an hypercall.

I didn't find generic helpers to do a these operations, so the change
is only arm32 specific.

Reported-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent 6e8f580d

arch/arm/xen/hypercall.S

+15 −0

Original line number	Diff line number	Diff line
		@@ -98,8 +98,23 @@ ENTRY(privcmd_call)
		mov r1, r2
		mov r2, r3
		ldr r3, [sp, #8]
		/*
		* 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]
		__HVC(XEN_IMM)

		/*
		* Disable userspace access from kernel. This is fine to do it
		* unconditionally as no set_fs(KERNEL_DS)/set_fs(get_ds()) is
		* called before.
		*/
		uaccess_disable r4

		ldm sp!, {r4}
		ret lr
		ENDPROC(privcmd_call);