firmware: coreboot: Check size of table entry and use flex-array

The memcpy() of the data following a coreboot_table_entry couldn't
be evaluated by the compiler under CONFIG_FORTIFY_SOURCE. To make it
easier to reason about, add an explicit flexible array member to struct
coreboot_device so the entire entry can be copied at once. Additionally,
validate the sizes before copying. Avoids this run-time false positive
warning:

  memcpy: detected field-spanning write (size 168) of single field "&device->entry" at drivers/firmware/google/coreboot_table.c:103 (size 8)

Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://lore.kernel.org/all/03ae2704-8c30-f9f0-215b-7cdf4ad35a9a@molgen.mpg.de/
Cc: Jack Rosenthal <jrosenth@chromium.org>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Julius Werner <jwerner@chromium.org>
Cc: Brian Norris <briannorris@chromium.org>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20230107031406.gonna.761-kees@kernel.org
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Link: https://lore.kernel.org/r/20230112230312.give.446-kees@kernel.org

diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
index 2652c39..33ae947 100644 (file)
--- a/drivers/firmware/google/coreboot_table.c
+++ b/drivers/firmware/google/coreboot_table.c
@@ -93,14 +93,19 @@ static int coreboot_table_populate(struct device *dev, void *ptr)
        for (i = 0; i < header->table_entries; i++) {
                entry = ptr_entry;
 
-               device = kzalloc(sizeof(struct device) + entry->size, GFP_KERNEL);
+               if (entry->size < sizeof(*entry)) {
+                       dev_warn(dev, "coreboot table entry too small!\n");
+                       return -EINVAL;
+               }
+
+               device = kzalloc(sizeof(device->dev) + entry->size, GFP_KERNEL);
                if (!device)
                        return -ENOMEM;
 
                device->dev.parent = dev;
                device->dev.bus = &coreboot_bus_type;
                device->dev.release = coreboot_device_release;
-               memcpy(&device->entry, ptr_entry, entry->size);
+               memcpy(device->raw, ptr_entry, entry->size);
 
                switch (device->entry.tag) {
                case LB_TAG_CBMEM_ENTRY:

diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index 37f4d33..d814dca 100644 (file)
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -79,6 +79,7 @@ struct coreboot_device {
                struct lb_cbmem_ref cbmem_ref;
                struct lb_cbmem_entry cbmem_entry;
                struct lb_framebuffer framebuffer;
+               DECLARE_FLEX_ARRAY(u8, raw);
        };
 };