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Subject[PATCH v2 07/10] powerpc/8xx: Add Kernel Userspace Access Protection
Date
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 restores SPRN_MD_AP
with the value saved on exception entry.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/include/asm/kup.h | 3 ++
arch/powerpc/include/asm/nohash/32/kup-8xx.h | 68 ++++++++++++++++++++++++++++
arch/powerpc/include/asm/nohash/32/mmu-8xx.h | 7 +++
arch/powerpc/mm/8xx_mmu.c | 12 +++++
arch/powerpc/platforms/Kconfig.cputype | 1 +
5 files changed, 91 insertions(+)
create mode 100644 arch/powerpc/include/asm/nohash/32/kup-8xx.h

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 632b367b93f4..75ade5a54607 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -5,6 +5,9 @@
#ifdef CONFIG_PPC64
#include <asm/book3s/64/kup-radix.h>
#endif
+#ifdef CONFIG_PPC_8xx
+#include <asm/nohash/32/kup-8xx.h>
+#endif

#ifdef __ASSEMBLY__
#ifndef CONFIG_PPC_KUAP
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
new file mode 100644
index 000000000000..a44cc6c1b901
--- /dev/null
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_KUP_8XX_H_
+#define _ASM_POWERPC_KUP_8XX_H_
+
+#include <asm/bug.h>
+
+#ifdef CONFIG_PPC_KUAP
+
+#ifdef __ASSEMBLY__
+
+.macro kuap_save_and_lock sp, thread, gpr1, gpr2, gpr3
+ lis \gpr2, MD_APG_KUAP@h /* only APG0 and APG1 are used */
+ mfspr \gpr1, SPRN_MD_AP
+ mtspr SPRN_MD_AP, \gpr2
+ stw \gpr1, STACK_REGS_KUAP(\sp)
+.endm
+
+.macro kuap_restore sp, current, gpr1, gpr2, gpr3
+ lwz \gpr1, STACK_REGS_KUAP(\sp)
+ mtspr SPRN_MD_AP, \gpr1
+.endm
+
+.macro kuap_check current, gpr
+#ifdef CONFIG_PPC_KUAP_DEBUG
+ mfspr \gpr, SPRN_MD_AP
+ rlwinm \gpr, \gpr, 16, 0xffff
+999: twnei \gpr, MD_APG_KUAP@h
+ EMIT_BUG_ENTRY 999b, __FILE__, __LINE__, (BUGFLAG_WARNING | BUGFLAG_ONCE)
+#endif
+.endm
+
+#else /* !__ASSEMBLY__ */
+
+#include <asm/reg.h>
+
+static inline void allow_user_access(void __user *to, const void __user *from,
+ unsigned long size)
+{
+ mtspr(SPRN_MD_AP, MD_APG_INIT);
+}
+
+static inline void prevent_user_access(void __user *to, const void __user *from,
+ unsigned long size)
+{
+ mtspr(SPRN_MD_AP, MD_APG_KUAP);
+}
+
+static inline void allow_read_from_user(const void __user *from, unsigned long size)
+{
+ allow_user_access(NULL, from, size);
+}
+
+static inline void allow_write_to_user(void __user *to, unsigned long size)
+{
+ allow_user_access(to, NULL, size);
+}
+
+static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write)
+{
+ return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xf0000000),
+ "Bug: fault blocked by AP register !");
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* CONFIG_PPC_KUAP */
+
+#endif /* _ASM_POWERPC_KUP_8XX_H_ */
diff --git a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
index 3cb743284e09..f620adef54fc 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
@@ -121,6 +121,13 @@
*/
#define MD_APG_INIT 0x4fffffff

+/*
+ * 0 => No user => 01 (all accesses performed according to page definition)
+ * 1 => User => 10 (all accesses performed according to swaped page definition)
+ * 2-16 => NA => 11 (all accesses performed as user iaw page definition)
+ */
+#define MD_APG_KUAP 0x6fffffff
+
/* 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/mm/8xx_mmu.c b/arch/powerpc/mm/8xx_mmu.c
index e257a0c9bd08..87648b58d295 100644
--- a/arch/powerpc/mm/8xx_mmu.c
+++ b/arch/powerpc/mm/8xx_mmu.c
@@ -225,3 +225,15 @@ void __init setup_kuep(bool disabled)
mtspr(SPRN_MI_AP, MI_APG_KUEP);
}
#endif
+
+#ifdef CONFIG_PPC_KUAP
+void __init setup_kuap(bool disabled)
+{
+ pr_info("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);
+}
+#endif
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 00fa0d110dcb..ab586963893a 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -35,6 +35,7 @@ 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
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