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Message-ID: <adb2b7c9-3472-2b9c-37e1-6150697d0940@c-s.fr>
Date: Thu, 21 Feb 2019 11:46:06 +0100
From: Christophe Leroy <christophe.leroy@....fr>
To: Russell Currey <ruscur@...sell.cc>, linuxppc-dev@...ts.ozlabs.org
Cc: mpe@...erman.id.au, npiggin@...il.com, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 3/7] powerpc/mm: Add a framework for Kernel Userspace
Access Protection
Le 21/02/2019 à 10:35, Russell Currey a écrit :
> From: Christophe Leroy <christophe.leroy@....fr>
>
> 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.
Should we also consider adding user_access_begin() and the 3 other
associated macros ?
See x86 for details.
Christophe
>
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> [ruscur: remove 64-bit exception handling code]
> Signed-off-by: Russell Currey <ruscur@...sell.cc>
> ---
> .../admin-guide/kernel-parameters.txt | 2 +-
> arch/powerpc/include/asm/exception-64e.h | 3 ++
> arch/powerpc/include/asm/exception-64s.h | 3 ++
> 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/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 ++++++
> 16 files changed, 127 insertions(+), 14 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 8448a56a9eb9..0a76dbb39011 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2808,7 +2808,7 @@
> 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..8ae2d7855cfe 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 UNLOCK_USER_ACCESS(reg)
> +#define LOCK_USER_ACCESS(reg)
> +
> #define EXCEPTION_PROLOG_0(area) \
> GET_PACA(r13); \
> std r9,area+EX_R9(r13); /* save r9 */ \
> diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
> index 88b38b37c21b..f85facf3739b 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(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 e3a731793ea2..9db6a4c7c058 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(addr, size)))
> - return __clear_user(addr, size);
> - return size;
> + if (likely(access_ok(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 0768dfd8a64e..f8f2268f8b12 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/process.c b/arch/powerpc/kernel/process.c
> index ce393df243aa..995ef82a583d 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 890d4ddd91d6..48e0c91e0083 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 ad65e336721a..5f4a5391f41e 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,
> @@ -456,9 +464,10 @@ 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 83f95a5565d6..ecaedfff9992 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);
> }
>
> #define CTOR(shift) static void ctor_##shift(void *addr) \
> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> index 410c3443652c..7fa5ddbdce12 100644
> --- a/arch/powerpc/platforms/Kconfig.cputype
> +++ b/arch/powerpc/platforms/Kconfig.cputype
> @@ -351,6 +351,18 @@ 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
>
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