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powerpc: Use mm_context vas_windows counter to issue CP_ABORT

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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: 9d2a4d7133 ("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
This commit is contained in:
Haren Myneni
2020-04-15 23:08:11 -07:00
committed by Michael Ellerman
parent 1d955f9818
commit c420644c0a
6 changed files with 48 additions and 34 deletions
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24
arch/powerpc/kernel/process.c
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@@ -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(&current->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