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// SPDX-License-Identifier: BSD-2-Clause-Patent
/*
* sbat.c - parse SBAT data from the .sbat section data
*/
#include "shim.h"
#include "ssp.h"
#include "ssp_var_defs.h"
extern struct {
UINT32 automatic_offset;
UINT32 latest_offset;
} sbat_var_payload_header;
static UINT8 sbat_policy = POLICY_NOTREAD;
static UINT8 ssp_policy = POLICY_NOTREAD;
EFI_STATUS
parse_sbat_section(char *section_base, size_t section_size,
size_t *n_entries,
struct sbat_section_entry ***entriesp)
{
struct sbat_section_entry *entry = NULL, **entries = NULL;
EFI_STATUS efi_status = EFI_SUCCESS;
list_t csv, *pos = NULL;
char * end = section_base + section_size - 1;
size_t allocsz = 0;
size_t n;
char *strtab;
if (!section_base || !section_size || !n_entries || !entriesp) {
dprint(L"section_base:0x%lx section_size:0x%lx\n",
section_base, section_size);
dprint(L"n_entries:0x%lx entriesp:0x%lx\n",
n_entries, entriesp);
return EFI_INVALID_PARAMETER;
}
INIT_LIST_HEAD(&csv);
efi_status =
parse_csv_data(section_base, end, SBAT_SECTION_COLUMNS, &csv);
if (EFI_ERROR(efi_status)) {
dprint(L"parse_csv_data failed: %r\n", efi_status);
return efi_status;
}
n = 0;
list_for_each(pos, &csv) {
struct csv_row * row;
size_t i;
row = list_entry(pos, struct csv_row, list);
if (row->n_columns < SBAT_SECTION_COLUMNS) {
efi_status = EFI_INVALID_PARAMETER;
dprint(L"row->n_columns:%lu SBAT_SECTION_COLUMNS:%lu\n",
row->n_columns, SBAT_SECTION_COLUMNS);
goto err;
}
allocsz += sizeof(struct sbat_section_entry *);
allocsz += sizeof(struct sbat_section_entry);
for (i = 0; i < row->n_columns; i++) {
if (row->columns[i][0] == '\000') {
dprint(L"row[%lu].columns[%lu][0] == '\\000'\n", n, i);
efi_status = EFI_INVALID_PARAMETER;
goto err;
}
allocsz += strlen(row->columns[i]) + 1;
}
n++;
}
/*
* Not necessarily actually an *error* since we eat newlines and
* the like; it could actually just be /empty/.
*/
if (n == 0)
goto out;
strtab = AllocateZeroPool(allocsz);
if (!strtab) {
efi_status = EFI_OUT_OF_RESOURCES;
goto err;
}
entries = (struct sbat_section_entry **)strtab;
strtab += sizeof(struct sbat_section_entry *) * n;
entry = (struct sbat_section_entry *)strtab;
strtab += sizeof(struct sbat_section_entry) * n;
n = 0;
list_for_each(pos, &csv) {
struct csv_row * row;
size_t i;
const char **ptrs[] = {
&entry->component_name,
&entry->component_generation,
&entry->vendor_name,
&entry->vendor_package_name,
&entry->vendor_version,
&entry->vendor_url,
};
row = list_entry(pos, struct csv_row, list);
for (i = 0; i < row->n_columns; i++) {
*(ptrs[i]) = strtab;
strtab = stpcpy(strtab, row->columns[i]) + 1;
}
entries[n] = entry;
entry++;
n++;
}
out:
*entriesp = entries;
*n_entries = n;
err:
free_csv_list(&csv);
return efi_status;
}
void
cleanup_sbat_section_entries(size_t n, struct sbat_section_entry **entries)
{
if (!n || !entries)
return;
FreePool(entries);
}
EFI_STATUS
verify_single_entry(struct sbat_section_entry *entry, struct sbat_var_entry *sbat_var_entry, bool *found)
{
UINT16 sbat_gen, sbat_var_gen;
if (strcmp((const char *)entry->component_name, (const char *)sbat_var_entry->component_name) == 0) {
dprint(L"component %a has a matching SBAT variable entry, verifying\n",
entry->component_name);
*found = true;
/*
* atoi returns zero for failed conversion, so essentially
* badly parsed component_generation will be treated as zero
*/
sbat_gen = atoi((const char *)entry->component_generation);
sbat_var_gen = atoi((const char *)sbat_var_entry->component_generation);
if (sbat_gen < sbat_var_gen) {
dprint(L"component %a, generation %d, was revoked by %s variable\n",
entry->component_name, sbat_gen, SBAT_VAR_NAME);
LogError(L"image did not pass SBAT verification\n");
return EFI_SECURITY_VIOLATION;
}
}
return EFI_SUCCESS;
}
void
cleanup_sbat_var(list_t *entries)
{
list_t *pos = NULL, *tmp = NULL;
struct sbat_var_entry *entry;
void *first = NULL;
list_for_each_safe(pos, tmp, entries) {
entry = list_entry(pos, struct sbat_var_entry, list);
if (first == NULL || (uintptr_t)entry < (uintptr_t)first)
first = entry;
list_del(&entry->list);
}
if (first)
FreePool(first);
}
EFI_STATUS
verify_sbat_helper(list_t *local_sbat_var, size_t n, struct sbat_section_entry **entries)
{
unsigned int i;
list_t *pos = NULL;
EFI_STATUS efi_status = EFI_SUCCESS;
struct sbat_var_entry *sbat_var_entry;
if (list_empty(local_sbat_var)) {
dprint(L"%s variable not present\n", SBAT_VAR_NAME);
return EFI_SUCCESS;
}
for (i = 0; i < n; i++) {
list_for_each(pos, local_sbat_var) {
bool found = false;
sbat_var_entry = list_entry(pos, struct sbat_var_entry, list);
efi_status = verify_single_entry(entries[i], sbat_var_entry, &found);
if (EFI_ERROR(efi_status))
goto out;
if (found)
break;
}
}
out:
dprint(L"finished verifying SBAT data: %r\n", efi_status);
return efi_status;
}
EFI_STATUS
verify_sbat(size_t n, struct sbat_section_entry **entries)
{
EFI_STATUS efi_status;
efi_status = verify_sbat_helper(&sbat_var, n, entries);
return efi_status;
}
EFI_STATUS
parse_sbat_var_data(list_t *entry_list, UINT8 *data, UINTN datasize)
{
struct sbat_var_entry *entry = NULL, **entries;
EFI_STATUS efi_status = EFI_SUCCESS;
list_t csv, *pos = NULL;
char * start = (char *)data;
char * end = (char *)data + datasize - 1;
size_t allocsz = 0;
size_t n;
char *strtab;
if (!entry_list|| !data || datasize == 0)
return EFI_INVALID_PARAMETER;
INIT_LIST_HEAD(&csv);
efi_status = parse_csv_data(start, end, SBAT_VAR_COLUMNS, &csv);
if (EFI_ERROR(efi_status)) {
return efi_status;
}
n = 0;
list_for_each(pos, &csv) {
struct csv_row * row;
size_t i;
row = list_entry(pos, struct csv_row, list);
if (row->n_columns < SBAT_VAR_REQUIRED_COLUMNS) {
efi_status = EFI_INVALID_PARAMETER;
goto err;
}
allocsz += sizeof(struct sbat_var_entry *);
allocsz += sizeof(struct sbat_var_entry);
for (i = 0; i < row->n_columns; i++) {
if (!row->columns[i][0]) {
efi_status = EFI_INVALID_PARAMETER;
goto err;
}
allocsz += strlen(row->columns[i]) + 1;
}
n++;
}
strtab = AllocateZeroPool(allocsz);
if (!strtab) {
efi_status = EFI_OUT_OF_RESOURCES;
goto err;
}
INIT_LIST_HEAD(entry_list);
entry = (struct sbat_var_entry *)strtab;
strtab += sizeof(struct sbat_var_entry) * n;
entries = (struct sbat_var_entry **)strtab;
strtab += sizeof(struct sbat_var_entry *) * n;
n = 0;
list_for_each(pos, &csv) {
struct csv_row * row;
size_t i;
const char **ptrs[] = {
&entry->component_name,
&entry->component_generation,
&entry->sbat_datestamp,
};
row = list_entry(pos, struct csv_row, list);
for (i = 0; i < row->n_columns; i++) {
*(ptrs[i]) = strtab;
strtab = stpcpy(strtab, row->columns[i]) + 1;
}
INIT_LIST_HEAD(&entry->list);
list_add_tail(&entry->list, entry_list);
entries[n] = entry;
entry++;
n++;
}
err:
free_csv_list(&csv);
return efi_status;
}
EFI_STATUS
parse_sbat_var(list_t *entries, char *sbat_var_candidate)
{
UINT8 *data = 0;
UINTN datasize;
EFI_STATUS efi_status;
list_t *pos = NULL;
if (!entries) {
dprint(L"entries is NULL\n");
return EFI_INVALID_PARAMETER;
}
if (sbat_var_candidate == NULL) {
dprint(L"sbat_var_candidate is NULL, reading variable\n");
efi_status = get_variable(SBAT_VAR_NAME, &data, &datasize, SHIM_LOCK_GUID);
if (EFI_ERROR(efi_status)) {
LogError(L"Failed to read SBAT variable\n", efi_status);
return efi_status;
}
} else {
datasize = strlen(sbat_var_candidate);
data = AllocatePool(datasize + 1);
memcpy(data, sbat_var_candidate, datasize);
}
/*
* We've intentionally made sure there's a NUL byte on all variable
* allocations, so use that here.
*/
efi_status = parse_sbat_var_data(entries, data, datasize+1);
if (EFI_ERROR(efi_status)) {
dprint(L"parse_sbat_var_data() failed datasize: %d\n", datasize);
goto out;
}
dprint(L"SBAT variable entries:\n");
list_for_each(pos, entries) {
struct sbat_var_entry *entry;
entry = list_entry(pos, struct sbat_var_entry, list);
dprint(L"%a, %a, %a\n", entry->component_name,
entry->component_generation, entry->sbat_datestamp);
}
out:
FreePool(data);
return efi_status;
}
static bool
check_sbat_var_attributes(UINT32 attributes)
{
#ifdef ENABLE_SHIM_DEVEL
return attributes == UEFI_VAR_NV_BS_RT;
#else
return attributes == UEFI_VAR_NV_BS ||
attributes == UEFI_VAR_NV_BS_TIMEAUTH;
#endif
}
static char *
nth_sbat_field(char *str, size_t limit, int n)
{
size_t i;
for (i = 0; i < limit && str[i] != '\0'; i++) {
if (n == 0)
return &str[i];
if (str[i] == ',')
n--;
}
return &str[i];
}
bool
preserve_sbat_uefi_variable(UINT8 *sbat, UINTN sbatsize, UINT32 attributes,
char *sbat_var)
{
char *sbatc = (char *)sbat;
char *current_version, *new_version,
*current_datestamp, *new_datestamp;
int current_version_len, new_version_len;
/* current metadata is not currupt somehow */
if (!check_sbat_var_attributes(attributes) ||
sbatsize < strlen(SBAT_VAR_ORIGINAL) ||
strncmp(sbatc, SBAT_VAR_SIG, strlen(SBAT_VAR_SIG)))
return false;
/* current metadata version not newer */
current_version = nth_sbat_field(sbatc, sbatsize, 1);
new_version = nth_sbat_field(sbat_var, strlen(sbat_var)+1, 1);
current_datestamp = nth_sbat_field(sbatc, sbatsize, 2);
new_datestamp = nth_sbat_field(sbat_var, strlen(sbat_var)+1, 2);
current_version_len = current_datestamp - current_version - 1;
new_version_len = new_datestamp - new_version - 1;
if (current_version_len > new_version_len ||
(current_version_len == new_version_len &&
strncmp(current_version, new_version, new_version_len) > 0))
return true;
/* current datestamp is not newer or idential */
if (strncmp(current_datestamp, new_datestamp,
strlen(SBAT_VAR_ORIGINAL_DATE)) >= 0)
return true;
return false;
}
/*
* This looks kind of weird, but it comes directly from the MS
* documentation:
* https://support.microsoft.com/en-us/topic/kb5027455-guidance-for-blocking-vulnerable-windows-boot-managers-522bb851-0a61-44ad-aa94-ad11119c5e91
*/
static UINT64
ssp_ver_to_ull(UINT16 *ver)
{
dprint("major: %u\n", ver[0]);
dprint("minor: %u\n", ver[1]);
dprint("rev: %u\n", ver[2]);
dprint("build: %u\n", ver[3]);
return ((UINT64)ver[0] << 48)
+ ((UINT64)ver[1] << 32)
+ ((UINT64)ver[2] << 16)
+ ver[3];
}
static bool
preserve_ssp_uefi_variable(UINT8 *ssp_applied, UINTN sspversize, UINT32 attributes,
uint8_t *ssp_candidate)
{
UINT64 old, new;
if (ssp_applied == NULL || ssp_candidate == NULL)
return false;
if (sspversize != SSPVER_SIZE)
return false;
if (!check_sbat_var_attributes(attributes))
return false;
old = ssp_ver_to_ull((UINT16 *)ssp_applied);
new = ssp_ver_to_ull((UINT16 *)ssp_candidate);
if (new > old)
return false;
else
return true;
}
static void
clear_sbat_policy()
{
EFI_STATUS efi_status = EFI_SUCCESS;
efi_status = del_variable(SBAT_POLICY, SHIM_LOCK_GUID);
if (EFI_ERROR(efi_status))
console_error(L"Could not reset SBAT Policy", efi_status);
}
EFI_STATUS
set_sbat_uefi_variable(char *sbat_var_automatic, char *sbat_var_latest)
{
EFI_STATUS efi_status = EFI_SUCCESS;
UINT32 attributes = 0;
UINT8 *sbat = NULL;
UINT8 *sbat_policyp = NULL;
UINTN sbatsize = 0;
UINTN sbat_policysize = 0;
char *sbat_var_candidate = NULL;
bool reset_sbat = false;
if (sbat_policy == POLICY_NOTREAD) {
efi_status = get_variable_attr(SBAT_POLICY, &sbat_policyp,
&sbat_policysize, SHIM_LOCK_GUID,
&attributes);
if (!EFI_ERROR(efi_status)) {
sbat_policy = *sbat_policyp;
clear_sbat_policy();
}
}
if (EFI_ERROR(efi_status)) {
dprint("Default sbat policy: automatic\n");
if (secure_mode()) {
sbat_var_candidate = sbat_var_automatic;
} else {
reset_sbat = true;
sbat_var_candidate = SBAT_VAR_ORIGINAL;
}
} else {
switch (sbat_policy) {
case POLICY_LATEST:
dprint("Custom sbat policy: latest\n");
sbat_var_candidate = sbat_var_latest;
break;
case POLICY_AUTOMATIC:
dprint("Custom sbat policy: automatic\n");
sbat_var_candidate = sbat_var_automatic;
break;
case POLICY_RESET:
if (secure_mode()) {
console_print(L"Cannot reset SBAT policy: Secure Boot is enabled.\n");
sbat_var_candidate = sbat_var_automatic;
} else {
dprint(L"Custom SBAT policy: reset OK\n");
reset_sbat = true;
sbat_var_candidate = SBAT_VAR_ORIGINAL;
}
break;
default:
console_error(L"SBAT policy state %llu is invalid",
EFI_INVALID_PARAMETER);
if (secure_mode()) {
sbat_var_candidate = sbat_var_automatic;
} else {
reset_sbat = true;
sbat_var_candidate = SBAT_VAR_ORIGINAL;
}
break;
}
}
efi_status = get_variable_attr(SBAT_VAR_NAME, &sbat, &sbatsize,
SHIM_LOCK_GUID, &attributes);
/*
* Always set the SbatLevel UEFI variable if it fails to read.
*/
if (EFI_ERROR(efi_status)) {
dprint(L"SBAT read failed %r\n", efi_status);
} else if (!reset_sbat &&
preserve_sbat_uefi_variable(sbat, sbatsize, attributes,
sbat_var_candidate)) {
dprint(L"preserving %s variable it is %d bytes, attributes are 0x%08x\n",
SBAT_VAR_NAME, sbatsize, attributes);
FreePool(sbat);
return EFI_SUCCESS;
} else {
FreePool(sbat);
/*
* parse the candidate SbatLevel and check that shim will not
* self revoke before writing SbatLevel variable
*/
dprint(L"shim SBAT reparse before application\n");
efi_status = parse_sbat_var(&sbat_var, sbat_var_candidate);
if (EFI_ERROR(efi_status)) {
dprint(L"proposed SbatLevel failed to parse\n");
return efi_status;
}
#ifndef SHIM_UNIT_TEST
char *sbat_start = (char *)&_sbat;
char *sbat_end = (char *)&_esbat;
efi_status = verify_sbat_section(sbat_start, sbat_end - sbat_start - 1);
if (EFI_ERROR(efi_status)) {
CHAR16 *title = L"New SbatLevel would self-revoke current shim. Not applied";
CHAR16 *message = L"Press any key to continue";
console_countdown(title, message, 10);
return efi_status;
}
#endif /* SHIM_UNIT_TEST */
/* delete previous variable */
dprint("%s variable is %d bytes, attributes are 0x%08x\n",
SBAT_VAR_NAME, sbatsize, attributes);
dprint("Deleting %s variable.\n", SBAT_VAR_NAME);
efi_status = set_variable(SBAT_VAR_NAME, SHIM_LOCK_GUID,
attributes, 0, "");
if (EFI_ERROR(efi_status)) {
dprint(L"%s variable delete failed %r\n", SBAT_VAR_NAME,
efi_status);
return efi_status;
}
}
/* set variable */
efi_status = set_variable(SBAT_VAR_NAME, SHIM_LOCK_GUID, SBAT_VAR_ATTRS,
strlen(sbat_var_candidate), sbat_var_candidate);
if (EFI_ERROR(efi_status)) {
dprint(L"%s variable writing failed %r\n", SBAT_VAR_NAME,
efi_status);
return efi_status;
}
/* verify that the expected data is there */
efi_status = get_variable(SBAT_VAR_NAME, &sbat, &sbatsize,
SHIM_LOCK_GUID);
if (EFI_ERROR(efi_status)) {
dprint(L"%s read failed %r\n", SBAT_VAR_NAME, efi_status);
return efi_status;
}
if (sbatsize != strlen(sbat_var_candidate) ||
strncmp((const char *)sbat, sbat_var_candidate,
strlen(sbat_var_candidate)) != 0) {
dprint("new sbatsize is %d, expected %d\n", sbatsize,
strlen(sbat_var_candidate));
efi_status = EFI_INVALID_PARAMETER;
} else {
dprint(L"%s variable initialization succeeded\n", SBAT_VAR_NAME);
}
FreePool(sbat);
return efi_status;
}
EFI_STATUS
set_sbat_uefi_variable_internal(void)
{
char *sbat_var_automatic;
char *sbat_var_latest;
sbat_var_automatic = (char *)&sbat_var_payload_header +
sbat_var_payload_header.automatic_offset;
sbat_var_latest = (char *)&sbat_var_payload_header +
sbat_var_payload_header.latest_offset;
return set_sbat_uefi_variable(sbat_var_automatic, sbat_var_latest);
}
static void
clear_ssp_policy(void)
{
EFI_STATUS efi_status = EFI_SUCCESS;
efi_status = del_variable(SSP_POLICY, SHIM_LOCK_GUID);
if (EFI_ERROR(efi_status))
console_error(L"Could not reset SSP Policy", efi_status);
}
static EFI_STATUS
clear_ssp_uefi_variables(void)
{
EFI_STATUS efi_status, rc = EFI_SUCCESS;
/* delete previous variable */
dprint("Deleting %s variable.\n", SSPVER_VAR_NAME);
efi_status = del_variable(SSPVER_VAR_NAME, SECUREBOOT_EFI_NAMESPACE_GUID);
if (EFI_ERROR(efi_status)) {
dprint(L"%s variable delete failed %r\n", SSPVER_VAR_NAME,
efi_status);
rc = efi_status;
}
dprint("Deleting %s variable.\n", SSPSIG_VAR_NAME);
efi_status = del_variable(SSPSIG_VAR_NAME, SECUREBOOT_EFI_NAMESPACE_GUID);
if (EFI_ERROR(efi_status)) {
dprint(L"%s variable delete failed %r\n", SSPSIG_VAR_NAME,
efi_status);
rc = efi_status;
}
return rc;
}
EFI_STATUS
set_ssp_uefi_variable(uint8_t *ssp_ver_automatic, uint8_t *ssp_sig_automatic,
uint8_t *ssp_ver_latest, uint8_t *ssp_sig_latest)
{
EFI_STATUS efi_status = EFI_SUCCESS;
UINT32 attributes = 0;
UINT8 *sspver = NULL;
UINT8 *policyp = NULL;
UINTN sspversize = 0;
UINTN policysize = 0;
uint8_t *ssp_ver = NULL;
uint8_t *ssp_sig = NULL;
bool reset_ssp = false;
_Static_assert(sizeof(SkuSiPolicyVersion) == SSPVER_SIZE,
"SkuSiPolicyVersion has unexpected size");
_Static_assert(sizeof(SkuSiPolicyUpdateSigners) == SSPSIG_SIZE,
"SkuSiPolicyUpdateSigners has unexpected size");
if (ssp_policy == POLICY_NOTREAD) {
efi_status = get_variable_attr(SSP_POLICY, &policyp,
&policysize, SHIM_LOCK_GUID,
&attributes);
if (!EFI_ERROR(efi_status)) {
ssp_policy = *policyp;
clear_ssp_policy();
}
}
if (EFI_ERROR(efi_status)) {
dprint("Default SSP policy: automatic\n");
ssp_ver = ssp_ver_automatic;
ssp_sig = ssp_sig_automatic;
} else {
switch (ssp_policy) {
case POLICY_LATEST:
dprint("Custom SSP policy: latest\n");\
ssp_ver = ssp_ver_latest;
ssp_sig = ssp_sig_latest;
break;
case POLICY_AUTOMATIC:
dprint("Custom SSP policy: automatic\n");
ssp_ver = ssp_ver_automatic;
ssp_sig = ssp_sig_automatic;
break;
case POLICY_RESET:
if (secure_mode()) {
console_print(L"Cannot reset SSP policy: Secure Boot is enabled.\n");
ssp_ver = ssp_ver_automatic;
ssp_sig = ssp_sig_automatic;
} else {
dprint(L"Custom SSP policy: reset OK\n");
reset_ssp = true;
}
break;
default:
console_error(L"SSP policy state %llu is invalid",
EFI_INVALID_PARAMETER);
ssp_ver = ssp_ver_automatic;
ssp_sig = ssp_sig_automatic;
break;
}
}
if (!ssp_ver && !ssp_sig && !reset_ssp) {
dprint(L"No supplied SSP data, not setting variables\n");
return EFI_SUCCESS;
}
efi_status = get_variable_attr(SSPVER_VAR_NAME, &sspver, &sspversize,
SECUREBOOT_EFI_NAMESPACE_GUID, &attributes);
/*
* Since generally we want bootmgr to manage its own revocations,
* we are much less agressive trying to set those variables
*/
if (EFI_ERROR(efi_status)) {
dprint(L"SkuSiPolicyVersion read failed %r\n", efi_status);
} else if (preserve_ssp_uefi_variable(sspver, sspversize, attributes, ssp_ver)
&& !reset_ssp) {
FreePool(sspver);
dprint(L"preserving %s variable it is %d bytes, attributes are 0x%08x\n",
SSPVER_VAR_NAME, sspversize, attributes);
return EFI_SUCCESS;
} else {
FreePool(sspver);
efi_status = clear_ssp_uefi_variables();
}
if (reset_ssp)
return efi_status;
/* set variable */
efi_status = set_variable(SSPVER_VAR_NAME, SECUREBOOT_EFI_NAMESPACE_GUID,
SSP_VAR_ATTRS, SSPVER_SIZE, ssp_ver);
if (EFI_ERROR(efi_status)) {
dprint(L"%s variable writing failed %r\n", SSPVER_VAR_NAME,
efi_status);
return efi_status;
}
dprint("done setting %s variable.\n", SSPSIG_VAR_NAME);
efi_status = set_variable(SSPSIG_VAR_NAME, SECUREBOOT_EFI_NAMESPACE_GUID,
SSP_VAR_ATTRS, SSPSIG_SIZE, ssp_sig);
if (EFI_ERROR(efi_status)) {
dprint(L"%s variable writing failed %r\n", SSPSIG_VAR_NAME,
efi_status);
return efi_status;
}
dprint("done setting %s variable.\n", SSPSIG_VAR_NAME);
return efi_status;
}
EFI_STATUS
set_ssp_uefi_variable_internal(void)
{
return set_ssp_uefi_variable(NULL, NULL, SkuSiPolicyVersion,
SkuSiPolicyUpdateSigners);
}
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