Systemd/src/basic/efivars.c

/* SPDX-License-Identifier: LGPL-2.1+ */

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <linux/fs.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>

#include "sd-id128.h"

#include "alloc-util.h"
#include "chattr-util.h"
#include "efivars.h"
#include "fd-util.h"
#include "io-util.h"
#include "macro.h"
#include "stdio-util.h"
#include "strv.h"
#include "time-util.h"
#include "utf8.h"
#include "virt.h"

#if ENABLE_EFI

char* efi_variable_path(sd_id128_t vendor, const char *name) {
        char *p;

        if (asprintf(&p,
                     "/sys/firmware/efi/efivars/%s-" SD_ID128_UUID_FORMAT_STR,
                     name, SD_ID128_FORMAT_VAL(vendor)) < 0)
                return NULL;

        return p;
}

int efi_get_variable(
                sd_id128_t vendor,
                const char *name,
                uint32_t *ret_attribute,
                void **ret_value,
                size_t *ret_size) {

        _cleanup_close_ int fd = -1;
        _cleanup_free_ char *p = NULL;
        _cleanup_free_ void *buf = NULL;
        struct stat st;
        uint32_t a;
        ssize_t n;

        assert(name);

        p = efi_variable_path(vendor, name);
        if (!p)
                return -ENOMEM;

        if (!ret_value && !ret_size && !ret_attribute) {
                /* If caller is not interested in anything, just check if the variable exists and is readable
                 * to us. */
                if (access(p, R_OK) < 0)
                        return -errno;

                return 0;
        }

        fd = open(p, O_RDONLY|O_NOCTTY|O_CLOEXEC);
        if (fd < 0)
                return -errno;

        if (fstat(fd, &st) < 0)
                return -errno;
        if (st.st_size < 4)
                return -ENODATA;
        if (st.st_size > 4*1024*1024 + 4)
                return -E2BIG;

        if (ret_value || ret_attribute) {
                n = read(fd, &a, sizeof(a));
                if (n < 0)
                        return -errno;
                if (n != sizeof(a))
                        return -EIO;
        }

        if (ret_value) {
                buf = malloc(st.st_size - 4 + 2);
                if (!buf)
                        return -ENOMEM;

                n = read(fd, buf, (size_t) st.st_size - 4);
                if (n < 0)
                        return -errno;
                assert(n <= st.st_size - 4);

                /* Always NUL terminate (2 bytes, to protect UTF-16) */
                ((char*) buf)[n] = 0;
                ((char*) buf)[n + 1] = 0;
        } else
                /* Assume that the reported size is accurate */
                n = st.st_size - 4;

        /* Note that efivarfs interestingly doesn't require ftruncate() to update an existing EFI variable
         * with a smaller value. */

        if (ret_attribute)
                *ret_attribute = a;

        if (ret_value)
                *ret_value = TAKE_PTR(buf);

        if (ret_size)
                *ret_size = n;

        return 0;
}

int efi_get_variable_string(sd_id128_t vendor, const char *name, char **p) {
        _cleanup_free_ void *s = NULL;
        size_t ss = 0;
        int r;
        char *x;

        r = efi_get_variable(vendor, name, NULL, &s, &ss);
        if (r < 0)
                return r;

        x = utf16_to_utf8(s, ss);
        if (!x)
                return -ENOMEM;

        *p = x;
        return 0;
}

int efi_set_variable(
                sd_id128_t vendor,
                const char *name,
                const void *value,
                size_t size) {

        struct var {
                uint32_t attr;
                char buf[];
        } _packed_ * _cleanup_free_ buf = NULL;
        _cleanup_free_ char *p = NULL;
        _cleanup_close_ int fd = -1;
        bool saved_flags_valid = false;
        unsigned saved_flags;
        int r;

        assert(name);
        assert(value || size == 0);

        p = efi_variable_path(vendor, name);
        if (!p)
                return -ENOMEM;

        /* Newer efivarfs protects variables that are not in a whitelist with FS_IMMUTABLE_FL by default, to protect
         * them for accidental removal and modification. We are not changing these variables accidentally however,
         * hence let's unset the bit first. */

        r = chattr_path(p, 0, FS_IMMUTABLE_FL, &saved_flags);
        if (r < 0 && r != -ENOENT)
                log_debug_errno(r, "Failed to drop FS_IMMUTABLE_FL flag from '%s', ignoring: %m", p);

        saved_flags_valid = r >= 0;

        if (size == 0) {
                if (unlink(p) < 0) {
                        r = -errno;
                        goto finish;
                }

                return 0;
        }

        fd = open(p, O_WRONLY|O_CREAT|O_NOCTTY|O_CLOEXEC, 0644);
        if (fd < 0) {
                r = -errno;
                goto finish;
        }

        buf = malloc(sizeof(uint32_t) + size);
        if (!buf) {
                r = -ENOMEM;
                goto finish;
        }

        buf->attr = EFI_VARIABLE_NON_VOLATILE|EFI_VARIABLE_BOOTSERVICE_ACCESS|EFI_VARIABLE_RUNTIME_ACCESS;
        memcpy(buf->buf, value, size);

        r = loop_write(fd, buf, sizeof(uint32_t) + size, false);
        if (r < 0)
                goto finish;

        r = 0;

finish:
        if (saved_flags_valid) {
                int q;

                /* Restore the original flags field, just in case */
                if (fd < 0)
                        q = chattr_path(p, saved_flags, FS_IMMUTABLE_FL, NULL);
                else
                        q = chattr_fd(fd, saved_flags, FS_IMMUTABLE_FL, NULL);
                if (q < 0)
                        log_debug_errno(q, "Failed to restore FS_IMMUTABLE_FL on '%s', ignoring: %m", p);
        }

        return r;
}

int efi_set_variable_string(sd_id128_t vendor, const char *name, const char *v) {
        _cleanup_free_ char16_t *u16 = NULL;

        u16 = utf8_to_utf16(v, strlen(v));
        if (!u16)
                return -ENOMEM;

        return efi_set_variable(vendor, name, u16, (char16_strlen(u16) + 1) * sizeof(char16_t));
}

bool is_efi_boot(void) {
        if (detect_container() > 0)
                return false;

        return access("/sys/firmware/efi/", F_OK) >= 0;
}

static int read_flag(const char *varname) {
        _cleanup_free_ void *v = NULL;
        uint8_t b;
        size_t s;
        int r;

        if (!is_efi_boot()) /* If this is not an EFI boot, assume the queried flags are zero */
                return 0;

        r = efi_get_variable(EFI_VENDOR_GLOBAL, varname, NULL, &v, &s);
        if (r < 0)
                return r;

        if (s != 1)
                return -EINVAL;

        b = *(uint8_t *)v;
        return !!b;
}

bool is_efi_secure_boot(void) {
        return read_flag("SecureBoot") > 0;
}

bool is_efi_secure_boot_setup_mode(void) {
        return read_flag("SetupMode") > 0;
}

int systemd_efi_options_variable(char **line) {
        const char *e;
        int r;

        assert(line);

        /* For testing purposes it is sometimes useful to be able to override this */
        e = secure_getenv("SYSTEMD_EFI_OPTIONS");
        if (e) {
                char *m;

                m = strdup(e);
                if (!m)
                        return -ENOMEM;

                *line = m;
                return 0;
        }

        r = efi_get_variable_string(EFI_VENDOR_SYSTEMD, "SystemdOptions", line);
        if (r == -ENOENT)
                return -ENODATA;

        return r;
}
#endif