acpi: make bios_linker_loader_add_checksum() API offset based

It should help to make clear that bios_linker works in terms
of offsets within a file. Also it should prevent mistakes
where user passes as arguments pointers to unrelated to file blobs.

While at it, considering that it's a ACPI checksum and
it's initial value must be 0, move checksum field zeroing
into bios_linker_loader_add_checksum() instead of doing it
at every call site manually before bios_linker_loader_add_checksum()
is called.

In addition add extra boundary checks.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
index d02583747f..123160a94e 100644
--- a/hw/acpi/aml-build.c
+++ b/hw/acpi/aml-build.c
@@ -1493,6 +1493,8 @@ build_header(BIOSLinker *linker, GArray *table_data,
              AcpiTableHeader *h, const char *sig, int len, uint8_t rev,
              const char *oem_id, const char *oem_table_id)
 {
+    unsigned tbl_offset = (char *)h - table_data->data;
+    unsigned checksum_offset = (char *)&h->checksum - table_data->data;
     memcpy(&h->signature, sig, 4);
     h->length = cpu_to_le32(len);
     h->revision = rev;
@@ -1513,10 +1515,9 @@ build_header(BIOSLinker *linker, GArray *table_data,
     h->oem_revision = cpu_to_le32(1);
     memcpy(h->asl_compiler_id, ACPI_BUILD_APPNAME4, 4);
     h->asl_compiler_revision = cpu_to_le32(1);
-    h->checksum = 0;
     /* Checksum to be filled in by Guest linker */
     bios_linker_loader_add_checksum(linker, ACPI_BUILD_TABLE_FILE,
-                                    h, len, &h->checksum);
+        tbl_offset, len, checksum_offset);
 }
 
 void *acpi_data_push(GArray *table_data, unsigned size)