BugLink: https://bugs.launchpad.net/bugs/1775771

[ Upstream commit bb19af81 ]

The current Branch History Rolling Buffer (BHRB) code does not check
for any privilege levels before updating the data from BHRB. This
could leak kernel addresses to userspace even when profiling only with
userspace privileges. Add proper checks to prevent it.
Acked-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>