This patch implements a framework for Kernel Userspace Access
Protection.
Then subarches will have to possibility to provide their own
implementation by providing setup_kuap() and lock/unlock_user_access()
Some platform will need to know the area accessed and whether it is
accessed from read, write or both. Therefore source, destination and
size and handed over to the two functions.
Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
Documentation/admin-guide/kernel-parameters.txt | 2 +-
arch/powerpc/include/asm/exception-64e.h | 3 ++
arch/powerpc/include/asm/exception-64s.h | 9 +++++-
arch/powerpc/include/asm/futex.h | 4 +++
arch/powerpc/include/asm/kup.h | 21 ++++++++++++++
arch/powerpc/include/asm/paca.h | 3 ++
arch/powerpc/include/asm/processor.h | 3 ++
arch/powerpc/include/asm/ptrace.h | 3 ++
arch/powerpc/include/asm/uaccess.h | 38 +++++++++++++++++++------
arch/powerpc/kernel/asm-offsets.c | 7 +++++
arch/powerpc/kernel/entry_32.S | 8 +++++-
arch/powerpc/kernel/entry_64.S | 16 +++++++++--
arch/powerpc/kernel/process.c | 3 ++
arch/powerpc/lib/checksum_wrappers.c | 4 +++
arch/powerpc/mm/fault.c | 17 ++++++++---
arch/powerpc/mm/init-common.c | 10 +++++++
arch/powerpc/platforms/Kconfig.cputype | 12 ++++++++
17 files changed, 146 insertions(+), 17 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 1103549363bb..0d059b141ff8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2792,7 +2792,7 @@
noexec=on: enable non-executable mappings (default)
noexec=off: disable non-executable mappings
- nosmap [X86]
+ nosmap [X86,PPC]
Disable SMAP (Supervisor Mode Access Prevention)
even if it is supported by processor.
diff --git a/arch/powerpc/include/asm/exception-64e.h
b/arch/powerpc/include/asm/exception-64e.h
index 555e22d5e07f..bf25015834ee 100644
--- a/arch/powerpc/include/asm/exception-64e.h
+++ b/arch/powerpc/include/asm/exception-64e.h
@@ -215,5 +215,8 @@ exc_##label##_book3e:
#define RFI_TO_USER \
rfi
+#define UNLOCK_USER_ACCESS(reg)
+#define LOCK_USER_ACCESS(reg)
+
#endif /* _ASM_POWERPC_EXCEPTION_64E_H */
diff --git a/arch/powerpc/include/asm/exception-64s.h
b/arch/powerpc/include/asm/exception-64s.h
index 3b4767ed3ec5..4d971ca1e69b 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -264,6 +264,9 @@ BEGIN_FTR_SECTION_NESTED(943)
\
std ra,offset(r13); \
END_FTR_SECTION_NESTED(ftr,ftr,943)
+#define LOCK_USER_ACCESS(reg)
+#define UNLOCK_USER_ACCESS(reg)
+
#define EXCEPTION_PROLOG_0(area) \
GET_PACA(r13); \
std r9,area+EX_R9(r13); /* save r9 */ \
@@ -500,7 +503,11 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
beq 4f; /* if from kernel mode */ \
ACCOUNT_CPU_USER_ENTRY(r13, r9, r10); \
SAVE_PPR(area, r9); \
-4: EXCEPTION_PROLOG_COMMON_2(area) \
+4: lbz r9,PACA_USER_ACCESS_ALLOWED(r13); \
+ cmpwi cr1,r9,0; \
+ beq 5f; \
+ LOCK_USER_ACCESS(r9); \
+5: EXCEPTION_PROLOG_COMMON_2(area) \
EXCEPTION_PROLOG_COMMON_3(n) \
ACCOUNT_STOLEN_TIME
diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
index 94542776a62d..32230f9a1c32 100644
--- a/arch/powerpc/include/asm/futex.h
+++ b/arch/powerpc/include/asm/futex.h
@@ -35,6 +35,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int
oparg, int *oval,
{
int oldval = 0, ret;
+ unlock_user_access(uaddr, NULL, sizeof(*uaddr));
pagefault_disable();
switch (op) {
@@ -62,6 +63,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int
oparg, int *oval,
if (!ret)
*oval = oldval;
+ lock_user_access(uaddr, NULL, sizeof(*uaddr));
return ret;
}
@@ -75,6 +77,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
return -EFAULT;
+ unlock_user_access(uaddr, NULL, sizeof(*uaddr));
__asm__ __volatile__ (
PPC_ATOMIC_ENTRY_BARRIER
"1: lwarx %1,0,%3 # futex_atomic_cmpxchg_inatomic\n\
@@ -95,6 +98,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
: "cc", "memory");
*uval = prev;
+ lock_user_access(uaddr, NULL, sizeof(*uaddr));
return ret;
}
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index af4b5f854ca4..2ac540fb488f 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -4,6 +4,8 @@
#ifndef __ASSEMBLY__
+#include <asm/pgtable.h>
+
void setup_kup(void);
#ifdef CONFIG_PPC_KUEP
@@ -12,6 +14,25 @@ void setup_kuep(bool disabled);
static inline void setup_kuep(bool disabled) { }
#endif
+#ifdef CONFIG_PPC_KUAP
+void setup_kuap(bool disabled);
+#else
+static inline void setup_kuap(bool disabled) { }
+static inline void unlock_user_access(void __user *to, const void __user *from,
+ unsigned long size) { }
+static inline void lock_user_access(void __user *to, const void __user *from,
+ unsigned long size) { }
+#endif
+
#endif /* !__ASSEMBLY__ */
+#ifndef CONFIG_PPC_KUAP
+
+#ifdef CONFIG_PPC32
+#define LOCK_USER_ACCESS(val, sp, sr, srmax, curr)
+#define REST_USER_ACCESS(val, sp, sr, srmax, curr)
+#endif
+
+#endif
+
#endif /* _ASM_POWERPC_KUP_H_ */
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index e843bc5d1a0f..56236f6d8c89 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -169,6 +169,9 @@ struct paca_struct {
u64 saved_r1; /* r1 save for RTAS calls or PM or EE=0
*/
u64 saved_msr; /* MSR saved here by enter_rtas */
u16 trap_save; /* Used when bad stack is encountered */
+#ifdef CONFIG_PPC_KUAP
+ u8 user_access_allowed; /* can the kernel access user memory? */
+#endif
u8 irq_soft_mask; /* mask for irq soft masking */
u8 irq_happened; /* irq happened while soft-disabled */
u8 io_sync; /* writel() needs spin_unlock sync */
diff --git a/arch/powerpc/include/asm/processor.h
b/arch/powerpc/include/asm/processor.h
index ee58526cb6c2..4a9a10e86828 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -250,6 +250,9 @@ struct thread_struct {
#ifdef CONFIG_PPC32
void *pgdir; /* root of page-table tree */
unsigned long ksp_limit; /* if ksp <= ksp_limit stack overflow */
+#ifdef CONFIG_PPC_KUAP
+ unsigned long kuap; /* state of user access protection */
+#endif
#endif
/* Debug Registers */
struct debug_reg debug;
diff --git a/arch/powerpc/include/asm/ptrace.h
b/arch/powerpc/include/asm/ptrace.h
index 0b8a735b6d85..0321ba5b3d12 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -55,6 +55,9 @@ struct pt_regs
#ifdef CONFIG_PPC64
unsigned long ppr;
unsigned long __pad; /* Maintain 16 byte interrupt stack alignment */
+#elif defined(CONFIG_PPC_KUAP)
+ unsigned long kuap;
+ unsigned long __pad[3]; /* Maintain 16 byte interrupt stack alignment */
#endif
};
#endif
diff --git a/arch/powerpc/include/asm/uaccess.h
b/arch/powerpc/include/asm/uaccess.h
index 15bea9a0f260..b8f7f023fcbd 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -6,6 +6,7 @@
#include <asm/processor.h>
#include <asm/page.h>
#include <asm/extable.h>
+#include <asm/kup.h>
/*
* The fs value determines whether argument validity checking should be
@@ -141,6 +142,7 @@ extern long __put_user_bad(void);
#define __put_user_size(x, ptr, size, retval) \
do { \
retval = 0; \
+ unlock_user_access(ptr, NULL, size); \
switch (size) { \
case 1: __put_user_asm(x, ptr, retval, "stb"); break; \
case 2: __put_user_asm(x, ptr, retval, "sth"); break; \
@@ -148,6 +150,7 @@ do {
\
case 8: __put_user_asm2(x, ptr, retval); break; \
default: __put_user_bad(); \
} \
+ lock_user_access(ptr, NULL, size); \
} while (0)
#define __put_user_nocheck(x, ptr, size) \
@@ -240,6 +243,7 @@ do {
\
__chk_user_ptr(ptr); \
if (size > sizeof(x)) \
(x) = __get_user_bad(); \
+ unlock_user_access(NULL, ptr, size); \
switch (size) { \
case 1: __get_user_asm(x, ptr, retval, "lbz"); break; \
case 2: __get_user_asm(x, ptr, retval, "lhz"); break; \
@@ -247,6 +251,7 @@ do {
\
case 8: __get_user_asm2(x, ptr, retval); break; \
default: (x) = __get_user_bad(); \
} \
+ lock_user_access(NULL, ptr, size); \
} while (0)
/*
@@ -306,15 +311,21 @@ extern unsigned long __copy_tofrom_user(void __user *to,
static inline unsigned long
raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
{
- return __copy_tofrom_user(to, from, n);
+ unsigned long ret;
+
+ unlock_user_access(to, from, n);
+ ret = __copy_tofrom_user(to, from, n);
+ lock_user_access(to, from, n);
+ return ret;
}
#endif /* __powerpc64__ */
static inline unsigned long raw_copy_from_user(void *to,
const void __user *from, unsigned long n)
{
+ unsigned long ret;
if (__builtin_constant_p(n) && (n <= 8)) {
- unsigned long ret = 1;
+ ret = 1;
switch (n) {
case 1:
@@ -339,14 +350,18 @@ static inline unsigned long raw_copy_from_user(void *to,
}
barrier_nospec();
- return __copy_tofrom_user((__force void __user *)to, from, n);
+ unlock_user_access(NULL, from, n);
+ ret = __copy_tofrom_user((__force void __user *)to, from, n);
+ lock_user_access(NULL, from, n);
+ return ret;
}
static inline unsigned long raw_copy_to_user(void __user *to,
const void *from, unsigned long n)
{
+ unsigned long ret;
if (__builtin_constant_p(n) && (n <= 8)) {
- unsigned long ret = 1;
+ ret = 1;
switch (n) {
case 1:
@@ -366,17 +381,24 @@ static inline unsigned long raw_copy_to_user(void __user
*to,
return 0;
}
- return __copy_tofrom_user(to, (__force const void __user *)from, n);
+ unlock_user_access(to, NULL, n);
+ ret = __copy_tofrom_user(to, (__force const void __user *)from, n);
+ lock_user_access(to, NULL, n);
+ return ret;
}
extern unsigned long __clear_user(void __user *addr, unsigned long size);
static inline unsigned long clear_user(void __user *addr, unsigned long size)
{
+ unsigned long ret = size;
might_fault();
- if (likely(access_ok(VERIFY_WRITE, addr, size)))
- return __clear_user(addr, size);
- return size;
+ if (likely(access_ok(VERIFY_WRITE, addr, size))) {
+ unlock_user_access(addr, NULL, size);
+ ret = __clear_user(addr, size);
+ lock_user_access(addr, NULL, size);
+ }
+ return ret;
}
extern long strncpy_from_user(char *dst, const char __user *src, long count);
diff --git a/arch/powerpc/kernel/asm-offsets.c
b/arch/powerpc/kernel/asm-offsets.c
index 9ffc72ded73a..98e94299e728 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -93,6 +93,9 @@ int main(void)
OFFSET(THREAD_INFO, task_struct, stack);
DEFINE(THREAD_INFO_GAP, _ALIGN_UP(sizeof(struct thread_info), 16));
OFFSET(KSP_LIMIT, thread_struct, ksp_limit);
+#ifdef CONFIG_PPC_KUAP
+ OFFSET(KUAP, thread_struct, kuap);
+#endif
#endif /* CONFIG_PPC64 */
#ifdef CONFIG_LIVEPATCH
@@ -260,6 +263,7 @@ int main(void)
OFFSET(ACCOUNT_STARTTIME_USER, paca_struct, accounting.starttime_user);
OFFSET(ACCOUNT_USER_TIME, paca_struct, accounting.utime);
OFFSET(ACCOUNT_SYSTEM_TIME, paca_struct, accounting.stime);
+ OFFSET(PACA_USER_ACCESS_ALLOWED, paca_struct, user_access_allowed);
OFFSET(PACA_TRAP_SAVE, paca_struct, trap_save);
OFFSET(PACA_NAPSTATELOST, paca_struct, nap_state_lost);
OFFSET(PACA_SPRG_VDSO, paca_struct, sprg_vdso);
@@ -320,6 +324,9 @@ int main(void)
*/
STACK_PT_REGS_OFFSET(_DEAR, dar);
STACK_PT_REGS_OFFSET(_ESR, dsisr);
+#ifdef CONFIG_PPC_KUAP
+ STACK_PT_REGS_OFFSET(_KUAP, kuap);
+#endif
#else /* CONFIG_PPC64 */
STACK_PT_REGS_OFFSET(SOFTE, softe);
STACK_PT_REGS_OFFSET(_PPR, ppr);
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 77decded1175..64cb6f65ab53 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -36,6 +36,7 @@
#include <asm/asm-405.h>
#include <asm/feature-fixups.h>
#include <asm/barrier.h>
+#include <asm/kup.h>
/*
* MSR_KERNEL is > 0x10000 on 4xx/Book-E since it include MSR_CE.
@@ -156,6 +157,7 @@ transfer_to_handler:
stw r12,_CTR(r11)
stw r2,_XER(r11)
mfspr r12,SPRN_SPRG_THREAD
+ LOCK_USER_ACCESS(r2, r11, r9, r0, r12)
addi r2,r12,-THREAD
tovirt(r2,r2) /* set r2 to current */
beq 2f /* if from user, fix up THREAD.regs */
@@ -442,6 +444,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
ACCOUNT_CPU_USER_EXIT(r4, r5, r7)
3:
#endif
+ REST_USER_ACCESS(r7, r1, r4, r5, r2)
lwz r4,_LINK(r1)
lwz r5,_CCR(r1)
mtlr r4
@@ -739,7 +742,8 @@ fast_exception_return:
beq 1f /* if not, we've got problems */
#endif
-2: REST_4GPRS(3, r11)
+2: REST_USER_ACCESS(r3, r11, r4, r5, r2)
+ REST_4GPRS(3, r11)
lwz r10,_CCR(r11)
REST_GPR(1, r11)
mtcr r10
@@ -957,6 +961,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_47x)
1:
#endif /* CONFIG_TRACE_IRQFLAGS */
+ REST_USER_ACCESS(r3, r1, r4, r5, r2)
+
lwz r0,GPR0(r1)
lwz r2,GPR2(r1)
REST_4GPRS(3, r1)
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 7b1693adff2a..d5879f32bd34 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -297,7 +297,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
b . /* prevent speculative execution */
/* exit to kernel */
-1: ld r2,GPR2(r1)
+1: /* if the AMR was unlocked before, unlock it again */
+ lbz r2,PACA_USER_ACCESS_ALLOWED(r13)
+ cmpwi cr1,0
+ bne 2f
+ UNLOCK_USER_ACCESS(r2)
+2: ld r2,GPR2(r1)
ld r1,GPR1(r1)
mtlr r4
mtcr r5
@@ -983,7 +988,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
RFI_TO_USER
b . /* prevent speculative execution */
-1: mtspr SPRN_SRR1,r3
+1: /* exit to kernel */
+ /* if the AMR was unlocked before, unlock it again */
+ lbz r2,PACA_USER_ACCESS_ALLOWED(r13)
+ cmpwi cr1,0
+ bne 2f
+ UNLOCK_USER_ACCESS(r2)
+
+2: mtspr SPRN_SRR1,r3
ld r2,_CCR(r1)
mtcrf 0xFF,r2
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 96f34730010f..d57bc0d90e18 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1771,6 +1771,9 @@ void start_thread(struct pt_regs *regs, unsigned long
start, unsigned long sp)
regs->mq = 0;
regs->nip = start;
regs->msr = MSR_USER;
+#ifdef CONFIG_PPC_KUAP
+ regs->kuap = KUAP_START;
+#endif
#else
if (!is_32bit_task()) {
unsigned long entry;
diff --git a/arch/powerpc/lib/checksum_wrappers.c
b/arch/powerpc/lib/checksum_wrappers.c
index a0cb63fb76a1..6d84d5e14ef5 100644
--- a/arch/powerpc/lib/checksum_wrappers.c
+++ b/arch/powerpc/lib/checksum_wrappers.c
@@ -28,6 +28,7 @@ __wsum csum_and_copy_from_user(const void __user *src, void
*dst,
{
unsigned int csum;
+ unlock_user_access(NULL, src, len);
might_sleep();
*err_ptr = 0;
@@ -60,6 +61,7 @@ __wsum csum_and_copy_from_user(const void __user *src, void
*dst,
}
out:
+ lock_user_access(NULL, src, len);
return (__force __wsum)csum;
}
EXPORT_SYMBOL(csum_and_copy_from_user);
@@ -69,6 +71,7 @@ __wsum csum_and_copy_to_user(const void *src, void __user
*dst, int len,
{
unsigned int csum;
+ unlock_user_access(dst, NULL, len);
might_sleep();
*err_ptr = 0;
@@ -97,6 +100,7 @@ __wsum csum_and_copy_to_user(const void *src, void __user
*dst, int len,
}
out:
+ lock_user_access(dst, NULL, len);
return (__force __wsum)csum;
}
EXPORT_SYMBOL(csum_and_copy_to_user);
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index e57bd46cf25b..7cea9d7fc5e8 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -223,9 +223,11 @@ static int mm_fault_error(struct pt_regs *regs, unsigned
long addr,
}
/* Is this a bad kernel fault ? */
-static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
+static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
+ int is_exec = TRAP(regs) == 0x400;
+
/* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on
others */
if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT |
DSISR_PROTFAULT))) {
@@ -236,7 +238,13 @@ static bool bad_kernel_fault(bool is_exec, unsigned long
error_code,
address, from_kuid(&init_user_ns,
current_uid()));
}
- return is_exec || (address >= TASK_SIZE);
+ if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
+ !search_exception_tables(regs->nip))
+ printk_ratelimited(KERN_CRIT "Kernel attempted to access user"
+ " page (%lx) - exploit attempt? (uid: %d)\n",
+ address, from_kuid(&init_user_ns,
+ current_uid()));
+ return is_exec || (address >= TASK_SIZE) ||
!search_exception_tables(regs->nip);
}
static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
@@ -442,9 +450,10 @@ static int __do_page_fault(struct pt_regs *regs, unsigned
long address,
/*
* The kernel should never take an execute fault nor should it
- * take a page fault to a kernel address.
+ * take a page fault to a kernel address or a page fault to a user
+ * address outside of dedicated places
*/
- if (unlikely(!is_user && bad_kernel_fault(is_exec, error_code,
address)))
+ if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address)))
return SIGSEGV;
/*
diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index 37f84a43b822..0fe98f62c58a 100644
--- a/arch/powerpc/mm/init-common.c
+++ b/arch/powerpc/mm/init-common.c
@@ -27,6 +27,7 @@
#include <asm/kup.h>
static bool disable_kuep = !IS_ENABLED(CONFIG_PPC_KUEP);
+static bool disable_kuap = !IS_ENABLED(CONFIG_PPC_KUAP);
static int __init parse_nosmep(char *p)
{
@@ -36,9 +37,18 @@ static int __init parse_nosmep(char *p)
}
early_param("nosmep", parse_nosmep);
+static int __init parse_nosmap(char *p)
+{
+ disable_kuap = true;
+ pr_warn("Disabling Kernel Userspace Access Protection\n");
+ return 0;
+}
+early_param("nosmap", parse_nosmap);
+
void __init setup_kup(void)
{
setup_kuep(disable_kuep);
+ setup_kuap(disable_kuap);
}
static void pgd_ctor(void *addr)
diff --git a/arch/powerpc/platforms/Kconfig.cputype
b/arch/powerpc/platforms/Kconfig.cputype
index 70830cb3c18a..68eaafd54aca 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -363,6 +363,18 @@ config PPC_KUEP
If you're unsure, say Y.
+config PPC_HAVE_KUAP
+ bool
+
+config PPC_KUAP
+ bool "Kernel Userspace Access Protection"
+ depends on PPC_HAVE_KUAP
+ default y
+ help
+ Enable support for Kernel Userspace Access Protection (KUAP)
+
+ If you're unsure, say Y.
+
config ARCH_ENABLE_HUGEPAGE_MIGRATION
def_bool y
depends on PPC_BOOK3S_64 && HUGETLB_PAGE && MIGRATION
--
2.13.3
