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powerpc/32s: Allow disabling KUAP at boot time

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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>
[mpe: Export disable_kuap_key to fix build errors]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cd79e8008455fba5395d099f9bb1305c039b931c.1622708530.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2021-06-03 08:41:43 +00:00 committed by Michael Ellerman
parent 50d2f104cd
commit 6b4d630068
2 changed files with 34 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
arch/powerpc/include/asm/book3s/32/kup.h
View File

@ -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);
}

12
arch/powerpc/mm/book3s32/kuap.c
View File

@ -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)
{
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");
}