On Fri, Sep 04, 2026 at 01:42:55PM +0200, Luigi Leonardi wrote:
None of the directive handlers that place data at a byte_offset within
a parameter area validated that byte_offset actually falls within the
parameter area's size. A malformed IGVM file with byte_offset > size would
underflow the "size - byte_offset" computation used to determine
remaining space, wrapping to a huge value and defeating the size
check, then write out of bounds through param_entry->data +
byte_offset.
Add qigvm_find_param_validate(), which looks up the parameter area,
checks byte_offset against its size, and returns the offset-adjusted
data pointer and remaining size via output parameters instead of the
raw QIgvmParameterData entry. This keeps the byte_offset arithmetic in
one place instead of repeating param_entry->data + byte_offset and
param_entry->size - byte_offset at every call site.
Use it in the vp-count and environment-info handlers, adding an
explicit check that the fixed-size write fits in the remaining space.
Signed-off-by: Luigi Leonardi <[email protected]>
---
backends/igvm.c | 68 +++++++++++++++++++++++++++++++++++-------
include/system/igvm-internal.h | 6 ++++
2 files changed, 63 insertions(+), 11 deletions(-)
diff --git a/backends/igvm.c b/backends/igvm.c
index 7b7bdc72b7..8c07f2ce5e 100644
--- a/backends/igvm.c
+++ b/backends/igvm.c
@@ -101,6 +101,39 @@ qigvm_find_param_entry(QIgvm *igvm, uint32_t
parameter_area_index,
return NULL;
}
+/*
+ * Look up a parameter area and check that param->byte_offset falls within
+ * it, in one step. On success, *data and *size are set to the
+ * offset-adjusted write location and remaining space within the parameter
+ * area, so callers never need to touch param->byte_offset themselves.
+ */
+bool
+qigvm_find_param_validate(QIgvm *igvm, uint32_t parameter_area_index,
I'm not sure about the name, but I don't have anything better to
suggest, maybe qigvm_get_param_data() ?
+ const IGVM_VHS_PARAMETER *param,
+ uint8_t **data, uint32_t *size,
+ Error **errp)
+{
+ QIgvmParameterData *param_entry;
+
+ assert(data && size);
+
+ param_entry = qigvm_find_param_entry(igvm, parameter_area_index, errp);
+ if (!param_entry) {
+ return false;
+ }
All others qigvm_* functions returns 0 on success and != 0 on failure,
should we be consistent ?
Or maybe we can return the data pointer (with NULL as error).
+
+ if (param->byte_offset > param_entry->size) {
+ error_setg(errp,
+ "IGVM: byte_offset 0x%x exceeds parameter area size 0x%x",
+ param->byte_offset, param_entry->size);
+ return false;
+ }
+
+ *data = param_entry->data + param->byte_offset;
+ *size = param_entry->size - param->byte_offset;
+ return true;
+}
+
static int qigvm_directive_page_data(QIgvm *ctx, const uint8_t *header_data,
Error **errp);
static int qigvm_directive_vp_context(QIgvm *ctx, const uint8_t *header_data,
@@ -682,17 +715,24 @@ static int qigvm_directive_vp_count(QIgvm *ctx, const
uint8_t *header_data,
Error **errp)
{
const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data;
- QIgvmParameterData *param_entry;
+ uint8_t *data;
+ uint32_t size;
nit: following the previous param_entry, maybe we can call them
param_data and param_size all over the place.
uint32_t *vp_count;
CPUState *cpu;
- param_entry = qigvm_find_param_entry(ctx,
- param->parameter_area_index, errp);
- if (param_entry == NULL) {
+ if (!qigvm_find_param_validate(ctx, param->parameter_area_index, param,
+ &data, &size, errp)) {
+ return -1;
+ }
+
+ if (sizeof(*vp_count) > size) {
+ error_setg(errp,
+ "IGVM: vp-count parameter exceeds parameter area "
+ "defined in IGVM file");
return -1;
}
- vp_count = (uint32_t *)(param_entry->data + param->byte_offset);
+ vp_count = (uint32_t *)data;
*vp_count = 0;
CPU_FOREACH(cpu)
{
@@ -707,17 +747,23 @@ static int qigvm_directive_environment_info(QIgvm *ctx,
Error **errp)
{
const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data;
- QIgvmParameterData *param_entry;
+ uint8_t *data;
+ uint32_t size;
IgvmEnvironmentInfo *environmental_state;
- param_entry = qigvm_find_param_entry(ctx,
- param->parameter_area_index, errp);
- if (param_entry == NULL) {
+ if (!qigvm_find_param_validate(ctx, param->parameter_area_index, param,
+ &data, &size, errp)) {
+ return -1;
+ }
+
+ if (sizeof(*environmental_state) > size) {
+ error_setg(errp,
+ "IGVM: environment-info parameter exceeds parameter area "
+ "defined in IGVM file");
return -1;
}
- environmental_state =
- (IgvmEnvironmentInfo *)(param_entry->data + param->byte_offset);
+ environmental_state = (IgvmEnvironmentInfo *)data;
environmental_state->memory_is_shared = 1;
return 0;
diff --git a/include/system/igvm-internal.h b/include/system/igvm-internal.h
index 9e9fa1d9af..6526b5055c 100644
--- a/include/system/igvm-internal.h
+++ b/include/system/igvm-internal.h
@@ -81,4 +81,10 @@ QIgvmParameterData*
qigvm_find_param_entry(QIgvm *igvm, uint32_t parameter_area_index,
Error **errp);
+bool
+qigvm_find_param_validate(QIgvm *igvm, uint32_t parameter_area_index,
+ const IGVM_VHS_PARAMETER *param,
+ uint8_t **data, uint32_t *size,
+ Error **errp);
+
#endif
--
2.55.0
