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, 2 insertions, 3 deletions

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index b3ce5be77c..06d6204749 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -2458,11 +2458,10 @@ build_rsdp(GArray *rsdp_table, BIOSLinker *linker, unsigned rsdt_tbl_offset)
         ACPI_BUILD_RSDP_FILE, rsdt_pa_offset, rsdt_pa_size,
         ACPI_BUILD_TABLE_FILE, rsdt_tbl_offset);
 
-    rsdp->checksum = 0;
     /* Checksum to be filled by Guest linker */
     bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
-                                    rsdp, sizeof *rsdp,
-                                    &rsdp->checksum);
+        (char *)rsdp - rsdp_table->data, sizeof *rsdp,
+        (char *)&rsdp->checksum - rsdp_table->data);
 
     return rsdp_table;
 }