hw/uefi: add var-service-policy.c

kraxel · kraxel · commit 034cb968ca8f · 2025-03-04T12:01:42.000+01:00
Implement variable policies (Edk2VariablePolicyProtocol).

This EFI protocol allows to define restrictions for variables.
It also allows to lock down variables (disallow write access).

Signed-off-by: Gerd Hoffmann &lt;kraxel@redhat.com&gt;
Message-ID: &lt;20250225163031.1409078-10-kraxel@redhat.com&gt;
diff --git a/hw/uefi/var-service-policy.c b/hw/uefi/var-service-policy.c
@@ -0,0 +1,370 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * uefi vars device - VarCheckPolicyLibMmiHandler implementation
+ *
+ * variable policy specs:
+ * https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Library/VariablePolicyLib/ReadMe.md
+ */
+#include "qemu/osdep.h"
+#include "system/dma.h"
+#include "migration/vmstate.h"
+
+#include "hw/uefi/var-service.h"
+#include "hw/uefi/var-service-api.h"
+#include "hw/uefi/var-service-edk2.h"
+
+#include "trace/trace-hw_uefi.h"
+
+static void calc_policy(uefi_var_policy *pol);
+
+static int uefi_var_policy_post_load(void *opaque, int version_id)
+{
+    uefi_var_policy *pol = opaque;
+
+    calc_policy(pol);
+    return 0;
+}
+
+const VMStateDescription vmstate_uefi_var_policy = {
+    .name = "uefi-var-policy",
+    .post_load = uefi_var_policy_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(entry_size, uefi_var_policy),
+        VMSTATE_VBUFFER_ALLOC_UINT32(entry, uefi_var_policy,
+                                     0, NULL, entry_size),
+        VMSTATE_END_OF_LIST()
+    },
+};
+
+static void print_policy_entry(variable_policy_entry *pe)
+{
+    uint16_t *name = (void *)pe + pe->offset_to_name;
+
+    fprintf(stderr, "%s:\n", __func__);
+
+    fprintf(stderr, "    name ´");
+    while (*name) {
+        fprintf(stderr, "%c", *name);
+        name++;
+    }
+    fprintf(stderr, "', version=%d.%d, size=%d\n",
+            pe->version >> 16, pe->version & 0xffff, pe->size);
+
+    if (pe->min_size) {
+        fprintf(stderr, "    size min=%d\n", pe->min_size);
+    }
+    if (pe->max_size != UINT32_MAX) {
+        fprintf(stderr, "    size max=%u\n", pe->max_size);
+    }
+    if (pe->attributes_must_have) {
+        fprintf(stderr, "    attr must=0x%x\n", pe->attributes_must_have);
+    }
+    if (pe->attributes_cant_have) {
+        fprintf(stderr, "    attr cant=0x%x\n", pe->attributes_cant_have);
+    }
+    if (pe->lock_policy_type) {
+        fprintf(stderr, "    lock policy type %d\n", pe->lock_policy_type);
+    }
+}
+
+static gboolean wildcard_str_equal(uefi_var_policy *pol,
+                                   uefi_variable *var)
+{
+    return uefi_str_equal_ex(pol->name, pol->name_size,
+                             var->name, var->name_size,
+                             true);
+}
+
+static uefi_var_policy *find_policy(uefi_vars_state *uv, QemuUUID guid,
+                                    uint16_t *name, uint64_t name_size)
+{
+    uefi_var_policy *pol;
+
+    QTAILQ_FOREACH(pol, &uv->var_policies, next) {
+        if (!qemu_uuid_is_equal(&pol->entry->namespace, &guid)) {
+            continue;
+        }
+        if (!uefi_str_equal(pol->name, pol->name_size,
+                            name, name_size)) {
+            continue;
+        }
+        return pol;
+    }
+    return NULL;
+}
+
+static uefi_var_policy *wildcard_find_policy(uefi_vars_state *uv,
+                                             uefi_variable *var)
+{
+    uefi_var_policy *pol;
+
+    QTAILQ_FOREACH(pol, &uv->var_policies, next) {
+        if (!qemu_uuid_is_equal(&pol->entry->namespace, &var->guid)) {
+            continue;
+        }
+        if (!wildcard_str_equal(pol, var)) {
+            continue;
+        }
+        return pol;
+    }
+    return NULL;
+}
+
+static void calc_policy(uefi_var_policy *pol)
+{
+    variable_policy_entry *pe = pol->entry;
+    unsigned int i;
+
+    pol->name = (void *)pol->entry + pe->offset_to_name;
+    pol->name_size = pe->size - pe->offset_to_name;
+
+    for (i = 0; i < pol->name_size / 2; i++) {
+        if (pol->name[i] == '#') {
+            pol->hashmarks++;
+        }
+    }
+}
+
+uefi_var_policy *uefi_vars_add_policy(uefi_vars_state *uv,
+                                      variable_policy_entry *pe)
+{
+    uefi_var_policy *pol, *p;
+
+    pol = g_new0(uefi_var_policy, 1);
+    pol->entry = g_malloc(pe->size);
+    memcpy(pol->entry, pe, pe->size);
+    pol->entry_size = pe->size;
+
+    calc_policy(pol);
+
+    /* keep list sorted by priority, add to tail of priority group */
+    QTAILQ_FOREACH(p, &uv->var_policies, next) {
+        if ((p->hashmarks > pol->hashmarks) ||
+            (!p->name_size && pol->name_size)) {
+            QTAILQ_INSERT_BEFORE(p, pol, next);
+            return pol;
+        }
+    }
+
+    QTAILQ_INSERT_TAIL(&uv->var_policies, pol, next);
+    return pol;
+}
+
+efi_status uefi_vars_policy_check(uefi_vars_state *uv,
+                                  uefi_variable *var,
+                                  gboolean is_newvar)
+{
+    uefi_var_policy *pol;
+    variable_policy_entry *pe;
+    variable_lock_on_var_state *lvarstate;
+    uint16_t *lvarname;
+    size_t lvarnamesize;
+    uefi_variable *lvar;
+
+    if (!uv->end_of_dxe) {
+        return EFI_SUCCESS;
+    }
+
+    pol = wildcard_find_policy(uv, var);
+    if (!pol) {
+        return EFI_SUCCESS;
+    }
+    pe = pol->entry;
+
+    uefi_trace_variable(__func__, var->guid, var->name, var->name_size);
+    print_policy_entry(pe);
+
+    if ((var->attributes & pe->attributes_must_have) != pe->attributes_must_have) {
+        trace_uefi_vars_policy_deny("must-have-attr");
+        return EFI_INVALID_PARAMETER;
+    }
+    if ((var->attributes & pe->attributes_cant_have) != 0) {
+        trace_uefi_vars_policy_deny("cant-have-attr");
+        return EFI_INVALID_PARAMETER;
+    }
+
+    if (var->data_size < pe->min_size) {
+        trace_uefi_vars_policy_deny("min-size");
+        return EFI_INVALID_PARAMETER;
+    }
+    if (var->data_size > pe->max_size) {
+        trace_uefi_vars_policy_deny("max-size");
+        return EFI_INVALID_PARAMETER;
+    }
+
+    switch (pe->lock_policy_type) {
+    case VARIABLE_POLICY_TYPE_NO_LOCK:
+        break;
+
+    case VARIABLE_POLICY_TYPE_LOCK_NOW:
+        trace_uefi_vars_policy_deny("lock-now");
+        return EFI_WRITE_PROTECTED;
+
+    case VARIABLE_POLICY_TYPE_LOCK_ON_CREATE:
+        if (!is_newvar) {
+            trace_uefi_vars_policy_deny("lock-on-create");
+            return EFI_WRITE_PROTECTED;
+        }
+        break;
+
+    case VARIABLE_POLICY_TYPE_LOCK_ON_VAR_STATE:
+        lvarstate    = (void *)pol->entry + sizeof(*pe);
+        lvarname     = (void *)pol->entry + sizeof(*pe) + sizeof(*lvarstate);
+        lvarnamesize = pe->offset_to_name - sizeof(*pe) - sizeof(*lvarstate);
+
+        uefi_trace_variable(__func__, lvarstate->namespace,
+                            lvarname, lvarnamesize);
+        lvar = uefi_vars_find_variable(uv, lvarstate->namespace,
+                                          lvarname, lvarnamesize);
+        if (lvar && lvar->data_size == 1) {
+            uint8_t *value = lvar->data;
+            if (lvarstate->value == *value) {
+                return EFI_WRITE_PROTECTED;
+            }
+        }
+        break;
+    }
+
+    return EFI_SUCCESS;
+}
+
+void uefi_vars_policies_clear(uefi_vars_state *uv)
+{
+    uefi_var_policy *pol;
+
+    while (!QTAILQ_EMPTY(&uv->var_policies)) {
+        pol = QTAILQ_FIRST(&uv->var_policies);
+        QTAILQ_REMOVE(&uv->var_policies, pol, next);
+        g_free(pol->entry);
+        g_free(pol);
+    }
+}
+
+static size_t uefi_vars_mm_policy_error(mm_header *mhdr,
+                                        mm_check_policy *mchk,
+                                        uint64_t status)
+{
+    mchk->result = status;
+    return sizeof(*mchk);
+}
+
+static uint32_t uefi_vars_mm_check_policy_is_enabled(uefi_vars_state *uv,
+                                                     mm_header       *mhdr,
+                                                     mm_check_policy *mchk,
+                                                     void            *func)
+{
+    mm_check_policy_is_enabled *mpar = func;
+    size_t length;
+
+    length = sizeof(*mchk) + sizeof(*mpar);
+    if (mhdr->length < length) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+
+    mpar->state  = TRUE;
+    mchk->result = EFI_SUCCESS;
+    return sizeof(*mchk);
+}
+
+static uint32_t uefi_vars_mm_check_policy_register(uefi_vars_state *uv,
+                                                   mm_header       *mhdr,
+                                                   mm_check_policy *mchk,
+                                                   void            *func)
+{
+    variable_policy_entry *pe = func;
+    uefi_var_policy *pol;
+    uint64_t length;
+
+    if (uadd64_overflow(sizeof(*mchk), pe->size, &length)) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+    if (mhdr->length < length) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+    if (pe->size < sizeof(*pe)) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+    if (pe->offset_to_name < sizeof(*pe)) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+
+    if (pe->lock_policy_type == VARIABLE_POLICY_TYPE_LOCK_ON_VAR_STATE &&
+        pe->offset_to_name < sizeof(*pe) + sizeof(variable_lock_on_var_state)) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+
+    /* check space for minimum string length */
+    if (pe->size < (size_t)pe->offset_to_name) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_BAD_BUFFER_SIZE);
+    }
+
+    if (!uefi_str_is_valid((void *)pe + pe->offset_to_name,
+                           pe->size - pe->offset_to_name,
+                           false)) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_INVALID_PARAMETER);
+    }
+
+    pol = find_policy(uv, pe->namespace,
+                      (void *)pe + pe->offset_to_name,
+                      pe->size - pe->offset_to_name);
+    if (pol) {
+        return uefi_vars_mm_policy_error(mhdr, mchk, EFI_ALREADY_STARTED);
+    }
+
+    uefi_vars_add_policy(uv, pe);
+
+    mchk->result = EFI_SUCCESS;
+    return sizeof(*mchk);
+}
+
+uint32_t uefi_vars_mm_check_policy_proto(uefi_vars_state *uv)
+{
+    static const char *fnames[] = {
+        "zero",
+        "disable",
+        "is-enabled",
+        "register",
+        "dump",
+        "lock",
+    };
+    const char      *fname;
+    mm_header       *mhdr = (mm_header *) uv->buffer;
+    mm_check_policy *mchk = (mm_check_policy *) (uv->buffer + sizeof(*mhdr));
+    void            *func = (uv->buffer + sizeof(*mhdr) + sizeof(*mchk));
+
+    if (mhdr->length < sizeof(*mchk)) {
+        return UEFI_VARS_STS_ERR_BAD_BUFFER_SIZE;
+    }
+
+    fname = mchk->command < ARRAY_SIZE(fnames)
+        ? fnames[mchk->command]
+        : "unknown";
+    trace_uefi_vars_policy_cmd(fname);
+
+    switch (mchk->command) {
+    case VAR_CHECK_POLICY_COMMAND_DISABLE:
+        mchk->result = EFI_UNSUPPORTED;
+        break;
+    case VAR_CHECK_POLICY_COMMAND_IS_ENABLED:
+        uefi_vars_mm_check_policy_is_enabled(uv, mhdr, mchk, func);
+        break;
+    case VAR_CHECK_POLICY_COMMAND_REGISTER:
+        if (uv->policy_locked) {
+            mchk->result = EFI_WRITE_PROTECTED;
+        } else {
+            uefi_vars_mm_check_policy_register(uv, mhdr, mchk, func);
+        }
+        break;
+    case VAR_CHECK_POLICY_COMMAND_LOCK:
+        uv->policy_locked = true;
+        mchk->result = EFI_SUCCESS;
+        break;
+    default:
+        mchk->result = EFI_UNSUPPORTED;
+        break;
+    }
+
+    uefi_trace_status(__func__, mchk->result);
+    return UEFI_VARS_STS_SUCCESS;
+}
