The DEXCR Non-Privileged Hash Instruction Enable (NPHIE) aspect controls
whether the hashst and hashchk instructions are treated as no-ops by the
CPU.
NPHIE behaviour per ISA 3.1B:
0: hashst and hashchk instructions are executed as no-ops
(even when allowed by PCR)
1: hashst and hashchk instructions are executed normally
(if allowed by PCR)
Currently this aspect may be set per-process by prctl() or enforced
globally by the hypervisor.
Add a kernel config option PPC_USER_ROP_PROTECT to enforce DEXCR[NPHIE]
globally regardless of prctl() or hypervisor. If set, don't report
NPHIE as editable via prctl(), as the prctl() value can never take
effect.
Signed-off-by: Benjamin Gray <bg...@linux.ibm.com>
---
arch/powerpc/Kconfig | 5 +++++
arch/powerpc/kernel/dexcr.c | 15 +++++++++++----
2 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 699df27b0e2f..ba3458d07744 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -434,6 +434,11 @@ config PGTABLE_LEVELS
default 2 if !PPC64
default 4
+config PPC_USER_ROP_PROTECT
+ bool
+ depends on PPC_BOOK3S_64
+ default y
+
source "arch/powerpc/sysdev/Kconfig"
source "arch/powerpc/platforms/Kconfig"
diff --git a/arch/powerpc/kernel/dexcr.c b/arch/powerpc/kernel/dexcr.c
index 8239bcc92026..394140fc23aa 100644
--- a/arch/powerpc/kernel/dexcr.c
+++ b/arch/powerpc/kernel/dexcr.c
@@ -2,6 +2,7 @@
#include <linux/capability.h>
#include <linux/cpu.h>
#include <linux/init.h>
+#include <linux/kconfig.h>
#include <linux/prctl.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
@@ -18,8 +19,8 @@
#define DEFAULT_DEXCR 0
/* Allow process configuration of these by default */
-#define DEXCR_PRCTL_EDITABLE (DEXCR_PRO_SBHE | DEXCR_PRO_IBRTPD | \
- DEXCR_PRO_SRAPD | DEXCR_PRO_NPHIE)
+static unsigned long dexcr_prctl_editable __ro_after_init =
+ DEXCR_PRO_SBHE | DEXCR_PRO_IBRTPD | DEXCR_PRO_SRAPD | DEXCR_PRO_NPHIE;
/*
* Lock to protect system DEXCR override from concurrent updates.
@@ -83,6 +84,12 @@ static int __init dexcr_init(void)
if (early_cpu_has_feature(CPU_FTR_DEXCR_SBHE))
update_userspace_system_dexcr(DEXCR_PRO_SBHE,
spec_branch_hint_enable);
+ if (early_cpu_has_feature(CPU_FTR_DEXCR_NPHIE) &&
+ IS_ENABLED(CONFIG_PPC_USER_ROP_PROTECT)) {
+ update_userspace_system_dexcr(DEXCR_PRO_NPHIE, 1);
+ dexcr_prctl_editable &= ~DEXCR_PRO_NPHIE;
+ }
+
return 0;
}
early_initcall(dexcr_init);
@@ -131,7 +138,7 @@ static int dexcr_aspect_get(struct task_struct *task,
unsigned int aspect)
{
int ret = 0;
- if (aspect & DEXCR_PRCTL_EDITABLE)
+ if (aspect & dexcr_prctl_editable)
ret |= PR_PPC_DEXCR_PRCTL;
if (aspect & task->thread.dexcr_mask) {
@@ -174,7 +181,7 @@ int dexcr_prctl_get(struct task_struct *task, unsigned long
which)
static int dexcr_aspect_set(struct task_struct *task, unsigned int aspect,
unsigned long ctrl)
{
- if (!(aspect & DEXCR_PRCTL_EDITABLE))
+ if (!(aspect & dexcr_prctl_editable))
return -ENXIO; /* Aspect is not allowed to be changed by prctl
*/
if (aspect & task->thread.dexcr_forced)
--
2.38.1
