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Subject[PATCH v2 04/10] powerpc/32: Prepare for Kernel Userspace Access Protection
Date
This patch adds ASM macros for saving, restoring and checking
the KUAP state, and modifies setup_32 to call them on exceptions
from kernel.

The macros are defined as empty by default for when CONFIG_PPC_KUAP
is not selected and/or for platforms which don't handle (yet) KUAP.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/include/asm/kup.h | 15 ++++++++++++++-
arch/powerpc/kernel/entry_32.S | 16 ++++++++++++----
arch/powerpc/platforms/Kconfig.cputype | 2 +-
3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index ccbd2a249575..632b367b93f4 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -6,7 +6,20 @@
#include <asm/book3s/64/kup-radix.h>
#endif

-#ifndef __ASSEMBLY__
+#ifdef __ASSEMBLY__
+#ifndef CONFIG_PPC_KUAP
+.macro kuap_save_and_lock sp, thread, gpr1, gpr2, gpr3
+.endm
+
+.macro kuap_restore sp, current, gpr1, gpr2, gpr3
+.endm
+
+.macro kuap_check current, gpr
+.endm
+
+#endif
+
+#else /* !__ASSEMBLY__ */

#include <asm/pgtable.h>

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index aaf7c5f44823..1182bf603d3c 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -36,6 +36,7 @@
#include <asm/asm-405.h>
#include <asm/feature-fixups.h>
#include <asm/barrier.h>
+#include <asm/kup.h>

/*
* MSR_KERNEL is > 0x10000 on 4xx/Book-E since it include MSR_CE.
@@ -150,8 +151,8 @@ transfer_to_handler:
stw r12,_CTR(r11)
stw r2,_XER(r11)
mfspr r12,SPRN_SPRG_THREAD
- addi r2,r12,-THREAD
beq 2f /* if from user, fix up THREAD.regs */
+ addi r2, r12, -THREAD
addi r11,r1,STACK_FRAME_OVERHEAD
stw r11,PT_REGS(r12)
#if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
@@ -186,6 +187,8 @@ transfer_to_handler:
2: /* if from kernel, check interrupted DOZE/NAP mode and
* check for stack overflow
*/
+ kuap_save_and_lock r11, r12, r9, r2, r0
+ addi r2, r12, -THREAD
lwz r9,KSP_LIMIT(r12)
cmplw r1,r9 /* if r1 <= ksp_limit */
ble- stack_ovf /* then the kernel stack overflowed */
@@ -272,6 +275,7 @@ reenable_mmu: /* re-enable mmu so we can */
lwz r9,_MSR(r11) /* if sleeping, clear MSR.EE */
rlwinm r9,r9,0,~MSR_EE
lwz r12,_LINK(r11) /* and return to address in LR */
+ kuap_restore r11, r2, r3, r4, r5
b fast_exception_return
#endif

@@ -423,6 +427,7 @@ BEGIN_FTR_SECTION
END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
stwcx. r0,0,r1 /* to clear the reservation */
ACCOUNT_CPU_USER_EXIT(r2, r5, r7)
+ kuap_check r2, r4
lwz r4,_LINK(r1)
lwz r5,_CCR(r1)
mtlr r4
@@ -673,6 +678,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_SPE)
stw r10,_CCR(r1)
stw r1,KSP(r3) /* Set old stack pointer */

+ kuap_check r2, r4
#ifdef CONFIG_SMP
/* We need a sync somewhere here to make sure that if the
* previous task gets rescheduled on another CPU, it sees all
@@ -861,12 +867,12 @@ resume_kernel:
/* check current_thread_info->preempt_count */
lwz r0,TI_PREEMPT(r2)
cmpwi 0,r0,0 /* if non-zero, just restore regs and return */
- bne restore
+ bne restore_kuap
andi. r8,r8,_TIF_NEED_RESCHED
- beq+ restore
+ beq+ restore_kuap
lwz r3,_MSR(r1)
andi. r0,r3,MSR_EE /* interrupts off? */
- beq restore /* don't schedule if so */
+ beq restore_kuap /* don't schedule if so */
#ifdef CONFIG_TRACE_IRQFLAGS
/* Lockdep thinks irqs are enabled, we need to call
* preempt_schedule_irq with IRQs off, so we inform lockdep
@@ -885,6 +891,8 @@ resume_kernel:
bl trace_hardirqs_on
#endif
#endif /* CONFIG_PREEMPT */
+restore_kuap:
+ kuap_restore r1, r2, r9, r10, r0

/* interrupts are hard-disabled at this point */
restore:
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 5e53b9fd62aa..2e45a6e2bc99 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -373,7 +373,7 @@ config PPC_KUAP

config PPC_KUAP_DEBUG
bool "Extra debugging for Kernel Userspace Access Protection"
- depends on PPC_HAVE_KUAP && PPC_RADIX_MMU
+ depends on PPC_HAVE_KUAP && (PPC_RADIX_MMU || PPC_32)
help
Add extra debugging for Kernel Userspace Access Protection (KUAP)
If you're unsure, say N.
--
2.13.3
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