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    SubjectRe: [PATCH v2 08/12] powerpc/32s: Allow disabling KUAP at boot time
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    Le 03/06/2021 à 10:41, Christophe Leroy a écrit :
    > 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 <christophe.leroy@csgroup.eu>
    > ---
    > 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;

    Same as 8xx, this needs to be exported for modules.

    > 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");
    > }
    >

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