[PATCH] powerpc/8xx: Allow disabling KUAP at boot time
flat view
STALE1955d
From: Christophe Leroy <hidden>
Date: 2021-06-03 09:02:08
Also in:
lkml
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
PPC64 uses MMU features to enable/disable KUAP at boot time.
But feature fixups are applied way too early on PPC32.
But since commit c16728835eec ("powerpc/32: Manage KUAP in C"),
all KUAP is in C so it is now possible to use static branches.
Signed-off-by: Christophe Leroy <redacted>
---
arch/powerpc/include/asm/nohash/32/kup-8xx.h | 41 ++++++++++++++++++--
arch/powerpc/mm/nohash/8xx.c | 10 +++--
2 files changed, 45 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
index 295ef5639609..04ed17db6d3c 100644
--- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h@@ -11,8 +11,18 @@ #include <asm/reg.h> +extern struct static_key_false disable_kuap_key; + +static __always_inline bool kuap_is_disabled(void) +{ + return static_branch_unlikely(&disable_kuap_key); +} + static inline void kuap_save_and_lock(struct pt_regs *regs) { + if (kuap_is_disabled()) + return; + regs->kuap = mfspr(SPRN_MD_AP); mtspr(SPRN_MD_AP, MD_APG_KUAP); }
@@ -23,12 +33,20 @@ static inline void kuap_user_restore(struct pt_regs *regs) static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap) { + if (kuap_is_disabled()) + return; + mtspr(SPRN_MD_AP, regs->kuap); } static inline unsigned long kuap_get_and_assert_locked(void) { - unsigned long kuap = mfspr(SPRN_MD_AP); + unsigned long kuap; + + if (kuap_is_disabled()) + return MD_APG_INIT; + + kuap = mfspr(SPRN_MD_AP); if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG)) WARN_ON_ONCE(kuap >> 16 != MD_APG_KUAP >> 16);
@@ -38,25 +56,36 @@ static inline unsigned long kuap_get_and_assert_locked(void) static inline void kuap_assert_locked(void) { - if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG)) + if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && !kuap_is_disabled()) kuap_get_and_assert_locked(); } static inline void allow_user_access(void __user *to, const void __user *from, unsigned long size, unsigned long dir) { + if (kuap_is_disabled()) + return; + mtspr(SPRN_MD_AP, MD_APG_INIT); } static inline void prevent_user_access(void __user *to, const void __user *from, unsigned long size, unsigned long dir) { + if (kuap_is_disabled()) + return; + mtspr(SPRN_MD_AP, MD_APG_KUAP); } static inline unsigned long prevent_user_access_return(void) { - unsigned long flags = mfspr(SPRN_MD_AP); + unsigned long flags; + + if (kuap_is_disabled()) + return MD_APG_INIT; + + flags = mfspr(SPRN_MD_AP); mtspr(SPRN_MD_AP, MD_APG_KUAP);
@@ -65,12 +94,18 @@ static inline unsigned long prevent_user_access_return(void) static inline void restore_user_access(unsigned long flags) { + if (kuap_is_disabled()) + return; + mtspr(SPRN_MD_AP, flags); } static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write) { + if (kuap_is_disabled()) + return false; + return !((regs->kuap ^ MD_APG_KUAP) & 0xff000000); }
diff --git a/arch/powerpc/mm/nohash/8xx.c b/arch/powerpc/mm/nohash/8xx.c
index 71bfdbedacee..a8d44e9342f3 100644
--- a/arch/powerpc/mm/nohash/8xx.c
+++ b/arch/powerpc/mm/nohash/8xx.c@@ -256,12 +256,16 @@ void __init setup_kuep(bool disabled) #endif #ifdef CONFIG_PPC_KUAP +struct static_key_false disable_kuap_key; + void __init setup_kuap(bool disabled) { - pr_info("Activating Kernel Userspace Access Protection\n"); + if (disabled) { + static_branch_enable(&disable_kuap_key); + return; + } - if (disabled) - pr_warn("KUAP cannot be disabled yet on 8xx when compiled in\n"); + pr_info("Activating Kernel Userspace Access Protection\n"); mtspr(SPRN_MD_AP, MD_APG_KUAP); }
--
2.25.0