PPC64 uses MMU features to enable/disable KUAP at boot time. But feature fixups are applied way too early on PPC32.
Now that all KUAP related actions are in C following the conversion of KUAP initial setup and context switch in C, static branches can be used to enable/disable KUAP. Signed-off-by: Christophe Leroy <[email protected]> --- arch/powerpc/include/asm/book3s/32/kup.h | 27 +++++++++++++++++++++++- arch/powerpc/mm/book3s32/kuap.c | 11 ++++++---- 2 files changed, 33 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h index 2854d970dabe..68fbe28c6d7e 100644 --- a/arch/powerpc/include/asm/book3s/32/kup.h +++ b/arch/powerpc/include/asm/book3s/32/kup.h @@ -9,11 +9,12 @@ #include <linux/jump_label.h> +extern struct static_key_false disable_kuap_key; extern struct static_key_false disable_kuep_key; static __always_inline bool kuap_is_disabled(void) { - return !IS_ENABLED(CONFIG_PPC_KUAP); + return !IS_ENABLED(CONFIG_PPC_KUAP) || static_branch_unlikely(&disable_kuap_key); } static __always_inline bool kuep_is_disabled(void) @@ -62,6 +63,9 @@ static inline void kuap_save_and_lock(struct pt_regs *regs) u32 addr = kuap & 0xf0000000; u32 end = kuap << 28; + if (kuap_is_disabled()) + return; + regs->kuap = kuap; if (unlikely(!kuap)) return; @@ -79,6 +83,9 @@ static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap) u32 addr = regs->kuap & 0xf0000000; u32 end = regs->kuap << 28; + if (kuap_is_disabled()) + return; + current->thread.kuap = regs->kuap; if (unlikely(regs->kuap == kuap)) @@ -91,6 +98,9 @@ static inline unsigned long kuap_get_and_assert_locked(void) { unsigned long kuap = current->thread.kuap; + if (kuap_is_disabled()) + return 0; + WARN_ON_ONCE(IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && kuap != 0); return kuap; @@ -106,6 +116,9 @@ static __always_inline void allow_user_access(void __user *to, const void __user { u32 addr, end; + if (kuap_is_disabled()) + return; + BUILD_BUG_ON(!__builtin_constant_p(dir)); BUILD_BUG_ON(dir & ~KUAP_READ_WRITE); @@ -128,6 +141,9 @@ static __always_inline void prevent_user_access(void __user *to, const void __us { u32 addr, end; + if (kuap_is_disabled()) + return; + BUILD_BUG_ON(!__builtin_constant_p(dir)); if (dir & KUAP_CURRENT_WRITE) { @@ -159,6 +175,9 @@ static inline unsigned long prevent_user_access_return(void) unsigned long end = flags << 28; void __user *to = (__force void __user *)addr; + if (kuap_is_disabled()) + return 0; + if (flags) prevent_user_access(to, to, end - addr, KUAP_READ_WRITE); @@ -171,6 +190,9 @@ static inline void restore_user_access(unsigned long flags) unsigned long end = flags << 28; void __user *to = (__force void __user *)addr; + if (kuap_is_disabled()) + return; + if (flags) allow_user_access(to, to, end - addr, KUAP_READ_WRITE); } @@ -181,6 +203,9 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write) unsigned long begin = regs->kuap & 0xf0000000; unsigned long end = regs->kuap << 28; + if (kuap_is_disabled()) + return false; + return is_write && (address < begin || address >= end); } diff --git a/arch/powerpc/mm/book3s32/kuap.c b/arch/powerpc/mm/book3s32/kuap.c index 5533ed92ab3d..a4ce6cdc28e5 100644 --- a/arch/powerpc/mm/book3s32/kuap.c +++ b/arch/powerpc/mm/book3s32/kuap.c @@ -3,15 +3,18 @@ #include <asm/kup.h> #include <asm/smp.h> +struct static_key_false disable_kuap_key; + void __init setup_kuap(bool disabled) { - kuap_update_sr(mfsr(0) | SR_KS, 0, TASK_SIZE); + if (!disabled) + kuap_update_sr(mfsr(0) | SR_KS, 0, TASK_SIZE); if (smp_processor_id() != boot_cpuid) return; - pr_info("Activating Kernel Userspace Access Protection\n"); - if (disabled) - pr_warn("KUAP cannot be disabled yet on 6xx when compiled in\n"); + static_branch_enable(&disable_kuap_key); + else + pr_info("Activating Kernel Userspace Access Protection\n"); } -- 2.25.0
