diff options
| author | Haren Myneni <haren@linux.ibm.com> | 2020-04-15 23:08:11 -0700 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-04-20 16:53:01 +1000 |
| commit | c420644c0a8f8839ca7269acbb8a3fc7fe1ec97d (patch) | |
| tree | 36c507a971a43af80e3a70537cd9ae3f75922edf /arch/powerpc/kernel/process.c | |
| parent | 1d955f981895464d8f112179a20bfdb92e6c63d4 (diff) | |
powerpc: Use mm_context vas_windows counter to issue CP_ABORT
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.
Moved set_thread_uses_vas() code to vas_tx_win_open() as this
functionality is needed only for userspace open windows. We are adding
VAS userspace support along with this fix. So no need to include this
fix in stable releases.
Fixes: 9d2a4d71332c ("powerpc: Define set_thread_uses_vas()")
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Reported-by: Nicholas Piggin <npiggin@gmail.com>
Suggested-by: Milton Miller <miltonm@us.ibm.com>
Suggested-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1587017291.2275.1077.camel@hbabu-laptop
Diffstat (limited to 'arch/powerpc/kernel/process.c')
| -rw-r--r-- | arch/powerpc/kernel/process.c | 24 |
1 files changed, 2 insertions, 22 deletions
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 9c21288f8645..8479c762aef2 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1228,7 +1228,8 @@ 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 */ @@ -1467,27 +1468,6 @@ void arch_setup_new_exec(void) } #endif -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 /** * Assign a TIDR (thread ID) for task @t and set it in the thread |