[PATCH V8 36/44] memremap_pages: Reserve a PKS PKey for eventual use by PMEM

ira.weiny
2022-01-27T17:56:36Z

From: Ira Weiny <ira.weiny@intel.com>

The persistent memory (PMEM) driver uses the memremap_pages facility to
provide 'struct page' metadata (vmemmap) for PMEM. Given that PMEM
capacity maybe orders of magnitude higher capacity than System RAM it
presents a large vulnerability surface to stray writes. Unlike stray
writes to System RAM, which may result in a crash or other undesirable
behavior, stray writes to PMEM additionally are more likely to result in
permanent data loss. Reboot is not a remediation for PMEM corruption
like it is for System RAM.

Given that PMEM access from the kernel is limited to a constrained set
of locations (PMEM driver, Filesystem-DAX, and direct-I/O to a DAX
page), it is amenable to supervisor pkey protection. PMEM uses the
memmap facility to map it's pages into the direct map.

Reserve a PKey for use by the memmap facility.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
include/linux/pks-keys.h | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/pks-keys.h b/include/linux/pks-keys.h
index a3fcd8df8688..46bb9a18da5a 100644
--- a/include/linux/pks-keys.h
+++ b/include/linux/pks-keys.h
@@ -42,14 +42,16 @@
*
*/
enum pks_pkey_consumers {
- PKS_KEY_DEFAULT = 0, /* Must be 0 for default PTE values */
- PKS_KEY_TEST = 1,
- PKS_KEY_NR_CONSUMERS = 2,
+ PKS_KEY_DEFAULT = 0, /* Must be 0 for default PTE values */
+ PKS_KEY_TEST = 1,
+ PKS_KEY_PGMAP_PROTECTION = 2,
+ PKS_KEY_NR_CONSUMERS = 3,
};

#define PKS_INIT_VALUE (PKR_RW_KEY(PKS_KEY_DEFAULT) | \
PKR_AD_KEY(PKS_KEY_TEST) | \
- PKR_AD_KEY(2) | PKR_AD_KEY(3) | \
+ PKR_AD_KEY(PKS_KEY_PGMAP_PROTECTION) | \
+ PKR_AD_KEY(3) | \
PKR_AD_KEY(4) | PKR_AD_KEY(5) | \
PKR_AD_KEY(6) | PKR_AD_KEY(7) | \
PKR_AD_KEY(8) | PKR_AD_KEY(9) | \
--
2.31.1