Commit 6b4d6300 authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

powerpc/32s: 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.

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: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Export disable_kuap_key to fix build errors]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cd79e8008455fba5395d099f9bb1305c039b931c.1622708530.git.christophe.leroy@csgroup.eu
parent 50d2f104

arch/powerpc/include/asm/book3s/32/kup.h

+26 −1
Original line number Diff line number Diff line
@@ -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);

}

arch/powerpc/mm/book3s32/kuap.c

+8 −4
Original line number Diff line number Diff line
@@ -3,15 +3,19 @@ 
#include <asm/kup.h>

#include <asm/smp.h>



struct static_key_false disable_kuap_key;

EXPORT_SYMBOL(disable_kuap_key);



void __init setup_kuap(bool disabled)

{

	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");

}