set_thread_uses_vas() sets used_vas flag for a process that opened VAS
window and issue CP_ABORT during context switch for only that process.
In multi-thread application, windows can be shared. For example Thread A
can open a window and Thread B can run COPY/PASTE instructions to send
NX request which may cause corruption or snooping or a covert channel.
Also once this flag is set, continue to run CP_ABORT even the VAS window
is closed.
So define vas-windows counter in process mm_context, increment this
counter for each window open and decrement it for window close. If
vas-windows is set, issue CP_ABORT during context switch. It means
clear the foreign real address mapping only if the process / thread uses
COPY/PASTE. Then disable it for that process if windows are not open.
Signed-off-by: Haren Myneni <ha...@linux.ibm.com>
Reported-by: Nicholas Piggin <npig...@gmail.com>
Suggested-by: Milton Miller <milt...@us.ibm.com>
Suggested-by: Nicholas Piggin <npig...@gmail.com>
---
arch/powerpc/include/asm/book3s/64/mmu.h | 3 +++
arch/powerpc/include/asm/mmu_context.h | 22 ++++++++++++++++++++++
arch/powerpc/include/asm/processor.h | 1 -
arch/powerpc/kernel/process.c | 8 ++++++--
arch/powerpc/platforms/powernv/vas-window.c | 1 +
5 files changed, 32 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h
b/arch/powerpc/include/asm/book3s/64/mmu.h
index bb3deb7..f0a9ff6 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -116,6 +116,9 @@ struct patb_entry {
/* Number of users of the external (Nest) MMU */
atomic_t copros;
+ /* Number of user space windows opened in process mm_context */
+ atomic_t vas_windows;
+
struct hash_mm_context *hash_context;
unsigned long vdso_base;
diff --git a/arch/powerpc/include/asm/mmu_context.h
b/arch/powerpc/include/asm/mmu_context.h
index 360367c..7fd249498 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -185,11 +185,33 @@ static inline void mm_context_remove_copro(struct
mm_struct *mm)
dec_mm_active_cpus(mm);
}
}
+
+/*
+ * vas_windows counter shows number of open windows in the mm
+ * context. During context switch, use this counter to clear the
+ * foreign real address mapping (CP_ABORT) for the thread / process
+ * that intend to use COPY/PASTE. When a process closes all windows,
+ * disable CP_ABORT which is expensive to run.
+ */
+static inline void mm_context_add_vas_windows(struct mm_struct *mm)
+{
+ atomic_inc(&mm->context.vas_windows);
+}
+
+static inline void mm_context_remove_vas_windows(struct mm_struct *mm)
+{
+ int c = atomic_dec_if_positive(&mm->context.vas_windows);
+
+ /* Detect imbalance between add and remove */
+ WARN_ON(c < 0);
+}
#else
static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
static inline void dec_mm_active_cpus(struct mm_struct *mm) { }
static inline void mm_context_add_copro(struct mm_struct *mm) { }
static inline void mm_context_remove_copro(struct mm_struct *mm) { }
+static inline void mm_context_add_vas_windows(struct mm_struct *mm) { }
+static inline void mm_context_remove_vas_windows(struct mm_struct *mm) { }
#endif
diff --git a/arch/powerpc/include/asm/processor.h
b/arch/powerpc/include/asm/processor.h
index eedcbfb..bfa336f 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -272,7 +272,6 @@ struct thread_struct {
unsigned mmcr0;
unsigned used_ebb;
- unsigned int used_vas;
#endif
};
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index fad50db..a3ecaf9 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1221,7 +1221,8 @@ struct task_struct *__switch_to(struct task_struct *prev,
* mappings, we must issue a cp_abort to clear any state and
* prevent snooping, corruption or a covert channel.
*/
- if (current->thread.used_vas)
+ if (current->mm &&
+ atomic_read(¤t->mm->context.vas_windows))
asm volatile(PPC_CP_ABORT);
}
#endif /* CONFIG_PPC_BOOK3S_64 */
@@ -1466,7 +1467,10 @@ int set_thread_uses_vas(void)
if (!cpu_has_feature(CPU_FTR_ARCH_300))
return -EINVAL;
- current->thread.used_vas = 1;
+ if (!current->mm)
+ return -EINVAL;
+
+ mm_context_add_vas_windows(current->mm);
/*
* Even a process that has no foreign real address mapping can use
diff --git a/arch/powerpc/platforms/powernv/vas-window.c
b/arch/powerpc/platforms/powernv/vas-window.c
index 3ffad5a..33dfbbf 100644
--- a/arch/powerpc/platforms/powernv/vas-window.c
+++ b/arch/powerpc/platforms/powernv/vas-window.c
@@ -1333,6 +1333,7 @@ int vas_win_close(struct vas_window *window)
put_pid(window->pid);
if (window->mm) {
mm_context_remove_copro(window->mm);
+ mm_context_remove_vas_windows(window->mm);
mmdrop(window->mm);
}
}
--
1.8.3.1
