[PATCH 4.16 062/272] powerpc/fscr: Enable interrupts earlier before calling get_user()

Greg Kroah-Hartman
2018-05-28T12:02:58Z

From: Anshuman Khandual <khandual@linux.vnet.ibm.com>

[ Upstream commit 709b973c844c0b4d115ac3a227a2e5a68722c912 ]

The function get_user() can sleep while trying to fetch instruction
from user address space and causes the following warning from the
scheduler.

BUG: sleeping function called from invalid context

Though interrupts get enabled back but it happens bit later after
get_user() is called. This change moves enabling these interrupts
earlier covering the function get_user(). While at this, lets check
for kernel mode and crash as this interrupt should not have been
triggered from the kernel context.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kernel/traps.c | 32 +++++++++++++++++---------------
1 file changed, 17 insertions(+), 15 deletions(-)

--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1612,6 +1612,22 @@ void facility_unavailable_exception(stru
value = mfspr(SPRN_FSCR);

status = value >> 56;
+ if ((hv || status >= 2) &&
+ (status < ARRAY_SIZE(facility_strings)) &&
+ facility_strings[status])
+ facility = facility_strings[status];
+
+ /* We should not have taken this interrupt in kernel */
+ if (!user_mode(regs)) {
+ pr_emerg("Facility '%s' unavailable (%d) exception in kernel mode at %lx\n",
+ facility, status, regs->nip);
+ die("Unexpected facility unavailable exception", regs, SIGABRT);
+ }
+
+ /* We restore the interrupt state now */
+ if (!arch_irq_disabled_regs(regs))
+ local_irq_enable();
+
if (status == FSCR_DSCR_LG) {
/*
* User is accessing the DSCR register using the problem
@@ -1678,25 +1694,11 @@ void facility_unavailable_exception(stru
return;
}

- if ((hv || status >= 2) &&
- (status < ARRAY_SIZE(facility_strings)) &&
- facility_strings[status])
- facility = facility_strings[status];
-
- /* We restore the interrupt state now */
- if (!arch_irq_disabled_regs(regs))
- local_irq_enable();
-
pr_err_ratelimited("%sFacility '%s' unavailable (%d), exception at 0x%lx, MSR=%lx\n",
hv ? "Hypervisor " : "", facility, status, regs->nip, regs->msr);

out:
- if (user_mode(regs)) {
- _exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
- return;
- }
-
- die("Unexpected facility unavailable exception", regs, SIGABRT);
+ _exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
}
#endif