tree 3ae572e2057a26a151957ccada417251121f41aa
parent c85061e6e0ee07e131b929e6a17bb2e20d19b321
author Nicholas Piggin <npiggin@gmail.com> 1526943600 +1000
committer Linus Torvalds <torvalds@linux-foundation.org> 1526960731 -0700

powerpc/64s: Add support for a store forwarding barrier at kernel entry/exit

On some CPUs we can prevent a vulnerability related to store-to-load
forwarding by preventing store forwarding between privilege domains,
by inserting a barrier in kernel entry and exit paths.

This is known to be the case on at least Power7, Power8 and Power9
powerpc CPUs.

Barriers must be inserted generally before the first load after moving
to a higher privilege, and after the last store before moving to a
lower privilege, HV and PR privilege transitions must be protected.

Barriers are added as patch sections, with all kernel/hypervisor entry
points patched, and the exit points to lower privilge levels patched
similarly to the RFI flush patching.

Firmware advertisement is not implemented yet, so CPU flush types
are hard coded.

Thanks to Michal Suchánek for bug fixes and review.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michal Suchánek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>