@@ -341,7 +341,9 @@ struct thread_struct {
unsigned long sier;
unsigned long mmcr2;
unsigned mmcr0;
+
unsigned used_ebb;
+ unsigned int used_vas;
#endif
};
@@ -92,6 +92,8 @@ static inline void clear_task_ebb(struct task_struct *t)
#endif
}
+extern int set_thread_uses_vas(void);
+
extern int set_thread_tidr(struct task_struct *t);
extern void clear_thread_tidr(struct task_struct *t);
@@ -1234,17 +1234,17 @@ struct task_struct *__switch_to(struct task_struct *prev,
* The copy-paste buffer can only store into foreign real
* addresses, so unprivileged processes can not see the
* data or use it in any way unless they have foreign real
- * mappings. We don't have a VAS driver that allocates those
- * yet, so no cpabort is required.
+ * mappings. If the new process has the foreign real address
+ * mappings, we must issue a cp_abort to clear any state and
+ * prevent snooping, corruption or a covert channel.
+ *
+ * DD1 allows paste into normal system memory so we do an
+ * unpaired copy, rather than cp_abort, to clear the buffer,
+ * since cp_abort is quite expensive.
*/
- if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {
- /*
- * DD1 allows paste into normal system memory, so we
- * do an unpaired copy here to clear the buffer and
- * prevent a covert channel being set up.
- *
- * cpabort is not used because it is quite expensive.
- */
+ if (new_thread->used_vas) {
+ asm volatile(PPC_CP_ABORT);
+ } else if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {
asm volatile(PPC_COPY(%0, %1)
: : "r"(dummy_copy_buffer), "r"(0));
}
@@ -1445,6 +1445,27 @@ void flush_thread(void)
#endif /* CONFIG_HAVE_HW_BREAKPOINT */
}
+int set_thread_uses_vas(void)
+{
+#ifdef CONFIG_PPC_BOOK3S_64
+ if (!cpu_has_feature(CPU_FTR_ARCH_300))
+ return -EINVAL;
+
+ current->thread.used_vas = 1;
+
+ /*
+ * Even a process that has no foreign real address mapping can use
+ * an unpaired COPY instruction (to no real effect). Issue CP_ABORT
+ * to clear any pending COPY and prevent a covert channel.
+ *
+ * __switch_to() will issue CP_ABORT on future context switches.
+ */
+ asm volatile(PPC_CP_ABORT);
+
+#endif /* CONFIG_PPC_BOOK3S_64 */
+ return 0;
+}
+
#ifdef CONFIG_PPC64
static DEFINE_SPINLOCK(vas_thread_id_lock);
static DEFINE_IDA(vas_thread_ida);
A CP_ABORT instruction is required in processes that have mapped a VAS "paste address" with the intention of using COPY/PASTE instructions. But since CP_ABORT is expensive, we want to restrict it to only processes that use/intend to use COPY/PASTE. Define an interface, set_thread_uses_vas(), that VAS can use to indicate that the current process opened a send window. During context switch, issue CP_ABORT only for processes that have the flag set. Thanks for input from Nick Piggin, Michael Ellerman. Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> --- Changelog[v3]: - [Nick Piggin] Rename interface to set_thread_uses_vas(), tweak comment and move the CP_ABORT from callers into the interface. --- arch/powerpc/include/asm/processor.h | 2 ++ arch/powerpc/include/asm/switch_to.h | 2 ++ arch/powerpc/kernel/process.c | 41 +++++++++++++++++++++++++++--------- 3 files changed, 35 insertions(+), 10 deletions(-)