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_ENFORCE_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 | 7 ++++++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 3aaadfd2c8eb..4851cb463dc0 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -473,6 +473,11 @@ config PGTABLE_LEVELS default 2 if !PPC64 default 4 +config PPC_USER_ENFORCE_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 e790f76787db..01d8fa28ca17 100644 --- a/arch/powerpc/kernel/dexcr.c +++ b/arch/powerpc/kernel/dexcr.c @@ -1,6 +1,8 @@ +#include <linux/cache.h> #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/sysctl.h> @@ -14,7 +16,7 @@ #define DEXCR_PRCTL_EDITABLE ( \ DEXCR_PR_IBRTPD | \ DEXCR_PR_SRAPD | \ - DEXCR_PR_NPHIE) + (!IS_ENABLED(CONFIG_PPC_USER_ENFORCE_ROP_PROTECT) ? DEXCR_PR_NPHIE : 0)) static unsigned long dexcr_supported __ro_after_init = 0; @@ -45,6 +47,9 @@ unsigned long get_thread_dexcr(struct thread_struct const *thread) { unsigned long dexcr = thread->dexcr_enabled; + if (IS_ENABLED(CONFIG_PPC_USER_ENFORCE_ROP_PROTECT)) + dexcr |= DEXCR_PR_NPHIE; + /* * spec_branch_hint_enable may be written to concurrently via sysctl. * The sysctl handler is careful to use WRITE_ONCE, so we avoid -- 2.41.0