From 9d2a4d71332cfdf4ea90754ad9b2f05a5ee5f6c7 Mon Sep 17 00:00:00 2001 From: Sukadev Bhattiprolu Date: Tue, 7 Nov 2017 18:23:54 -0800 Subject: [PATCH] powerpc: Define set_thread_uses_vas() 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. Signed-off-by: Sukadev Bhattiprolu [mpe: Fix to not use new_thread after _switch() returns] Signed-off-by: Michael Ellerman --- 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(-) diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h index 58cc212..bdab3b74 100644 --- a/arch/powerpc/include/asm/processor.h +++ b/arch/powerpc/include/asm/processor.h @@ -341,7 +341,9 @@ struct thread_struct { unsigned long sier; unsigned long mmcr2; unsigned mmcr0; + unsigned used_ebb; + unsigned int used_vas; #endif }; diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index f5da32f..07ff06e 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -91,6 +91,8 @@ 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); diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 887ae50..bfdd783 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1244,17 +1244,17 @@ 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 (current_thread_info()->task->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)); } @@ -1455,6 +1455,27 @@ 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); -- 2.7.4