[RFC PATCH v1 6/6] powerpc/8xx: Add Kernel Userspace Access Protection
From: Christophe Leroy
Date: Wed Nov 07 2018 - 11:56:44 EST
This patch adds Kernel Userspace Access Protection on the 8xx.
When a page is RO or RW, it is set RO or RW for Key 0 and NA
for Key 1.
Up to now, the User group is defined with Key 0 for both User and
Supervisor.
By changing the group to Key 0 for User and Key 1 for Supervisor,
this patch prevents the Kernel from being able to access user data.
At exception entry, the kernel saves SPRN_MD_AP in the regs struct,
and reapply the protection. At exception exit it restore SPRN_MD_AP
with the value it had on exception entry.
For the time being, the unused mq field of pt_regs struct is used for
that.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/include/asm/mmu-8xx.h | 7 +++++++
arch/powerpc/include/asm/nohash/32/pte-8xx.h | 23 +++++++++++++++++++++++
arch/powerpc/kernel/asm-offsets.c | 1 +
arch/powerpc/kernel/entry_32.S | 19 +++++++++++++++++++
arch/powerpc/kernel/process.c | 2 +-
arch/powerpc/mm/8xx_mmu.c | 10 ++++++++++
arch/powerpc/platforms/Kconfig.cputype | 1 +
7 files changed, 62 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/mmu-8xx.h b/arch/powerpc/include/asm/mmu-8xx.h
index 53dbf0788fce..bab8568def50 100644
--- a/arch/powerpc/include/asm/mmu-8xx.h
+++ b/arch/powerpc/include/asm/mmu-8xx.h
@@ -1,6 +1,7 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_POWERPC_MMU_8XX_H_
#define _ASM_POWERPC_MMU_8XX_H_
+
/*
* PPC8xx support
*/
@@ -120,6 +121,12 @@
*/
#define MD_APG_INIT 0x44444444
+/*
+ * 0 => No user => 01 (all accesses performed according to page definition)
+ * 1 => User => 10 (all accesses performed according to swaped page definition)
+ */
+#define MD_APG_KUAP 0x66666666
+
/* The effective page number register. When read, contains the information
* about the last instruction TLB miss. When MD_RPN is written, bits in
* this register are used to create the TLB entry.
diff --git a/arch/powerpc/include/asm/nohash/32/pte-8xx.h b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
index 6bfe041ef59d..f1ec7cf949d5 100644
--- a/arch/powerpc/include/asm/nohash/32/pte-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
@@ -135,6 +135,29 @@ static inline pte_t pte_mkhuge(pte_t pte)
}
#define pte_mkhuge pte_mkhuge
+
+#ifdef CONFIG_PPC_KUAP
+static inline void lock_user_wr_access(void)
+{
+ mtspr(SPRN_MD_AP, MD_APG_KUAP);
+}
+
+static inline void unlock_user_wr_access(void)
+{
+ mtspr(SPRN_MD_AP, MD_APG_INIT);
+}
+
+static inline void lock_user_rd_access(void)
+{
+ mtspr(SPRN_MD_AP, MD_APG_KUAP);
+}
+
+static inline void unlock_user_rd_access(void)
+{
+ mtspr(SPRN_MD_AP, MD_APG_INIT);
+}
+#endif
+
#endif
#endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 9ffc72ded73a..da2f5d011ddb 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -320,6 +320,7 @@ int main(void)
*/
STACK_PT_REGS_OFFSET(_DEAR, dar);
STACK_PT_REGS_OFFSET(_ESR, dsisr);
+ STACK_PT_REGS_OFFSET(_MQ, mq);
#else /* CONFIG_PPC64 */
STACK_PT_REGS_OFFSET(SOFTE, softe);
STACK_PT_REGS_OFFSET(_PPR, ppr);
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 77decded1175..7fd9dc16dd48 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -155,6 +155,13 @@ transfer_to_handler:
mfspr r2,SPRN_XER
stw r12,_CTR(r11)
stw r2,_XER(r11)
+#ifdef CONFIG_PPC_KUAP
+ mfspr r2, SPRN_MD_AP
+ stw r2, _MQ(r11)
+ lis r2, MD_APG_KUAP@h
+ ori r2, r2, MD_APG_KUAP@l
+ mtspr SPRN_MD_AP, r2
+#endif
mfspr r12,SPRN_SPRG_THREAD
addi r2,r12,-THREAD
tovirt(r2,r2) /* set r2 to current */
@@ -447,6 +454,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
mtlr r4
mtcr r5
lwz r7,_NIP(r1)
+#ifdef CONFIG_PPC_KUAP
+ lwz r2, _MQ(r1)
+ mtspr SPRN_MD_AP, r2
+#endif
lwz r2,GPR2(r1)
lwz r1,GPR1(r1)
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
@@ -745,6 +756,10 @@ fast_exception_return:
mtcr r10
lwz r10,_LINK(r11)
mtlr r10
+#ifdef CONFIG_PPC_KUAP
+ lwz r10, _MQ(r11)
+ mtspr SPRN_MD_AP, r10
+#endif
REST_GPR(10, r11)
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
mtspr SPRN_NRI, r0
@@ -997,6 +1012,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
.globl exc_exit_restart
exc_exit_restart:
lwz r12,_NIP(r1)
+#ifdef CONFIG_PPC_KUAP
+ lwz r10, _MQ(r1)
+ mtspr SPRN_MD_AP, r10
+#endif
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
mtspr SPRN_NRI, r0
#endif
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 96f34730010f..bbec29bda4cb 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1768,7 +1768,7 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
regs->trap &= ~1UL;
#ifdef CONFIG_PPC32
- regs->mq = 0;
+ regs->mq = MD_APG_KUAP;
regs->nip = start;
regs->msr = MSR_USER;
#else
diff --git a/arch/powerpc/mm/8xx_mmu.c b/arch/powerpc/mm/8xx_mmu.c
index 597d3bd2d9b5..acea296d4c76 100644
--- a/arch/powerpc/mm/8xx_mmu.c
+++ b/arch/powerpc/mm/8xx_mmu.c
@@ -204,3 +204,13 @@ void setup_kuep(bool disabled)
mtspr(SPRN_MI_AP, MI_APG_KUEP);
}
+
+void setup_kuap(bool disabled)
+{
+ pr_warn("Activating Kernel Userspace Access Protection\n");
+
+ if (disabled)
+ pr_warn("KUAP cannot be disabled yet on 8xx when compiled in\n");
+
+ mtspr(SPRN_MD_AP, MD_APG_KUAP);
+}
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index d1757cedf60b..a20669a9ec13 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -34,6 +34,7 @@ config PPC_8xx
select FSL_SOC
select SYS_SUPPORTS_HUGETLBFS
select PPC_HAVE_KUEP
+ select PPC_HAVE_KUAP
config 40x
bool "AMCC 40x"
--
2.13.3