Commit f6025a14 authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

powerpc/8xx: Allow disabling KUAP at boot time 



PPC64 uses MMU features to enable/disable KUAP at boot time.
But feature fixups are applied way too early on PPC32.

But since commit c1672883 ("powerpc/32: Manage KUAP in C"),
all KUAP is in C so it is now possible to use static branches.

Signed-off-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/3dca510ce555335261a47c4799167da698f569c0.1622782111.git.christophe.leroy@csgroup.eu
parent 10248dcb

arch/powerpc/include/asm/nohash/32/kup-8xx.h

+40 −3
Original line number Diff line number Diff line
@@ -9,10 +9,22 @@ 


#ifndef __ASSEMBLY__



#include <linux/jump_label.h>



#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 +35,20 @@ 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 +58,36 @@ 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 +96,18 @@ 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);

}

arch/powerpc/mm/nohash/8xx.c

+8 −3
Original line number Diff line number Diff line
@@ -256,12 +256,17 @@ void __init setup_kuep(bool disabled) 
#endif



#ifdef CONFIG_PPC_KUAP

struct static_key_false disable_kuap_key;

EXPORT_SYMBOL(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);

}