[PATCH AUTOSEL 5.15 24/24] firmware: coreboot: Check size of table entry and use flex-array

From: Sasha Levin
Date: Mon Jan 16 2023 - 09:15:06 EST


From: Kees Cook <keescook@xxxxxxxxxxxx>

[ Upstream commit 3b293487b8752cc42c1cbf8a0447bc6076c075fa ]

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@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/03ae2704-8c30-f9f0-215b-7cdf4ad35a9a@xxxxxxxxxxxxx/
Cc: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
Cc: Guenter Roeck <groeck@xxxxxxxxxxxx>
Cc: Julius Werner <jwerner@xxxxxxxxxxxx>
Cc: Brian Norris <briannorris@xxxxxxxxxxxx>
Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Julius Werner <jwerner@xxxxxxxxxxxx>
Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230107031406.gonna.761-kees@xxxxxxxxxx
Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Reviewed-by: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230112230312.give.446-kees@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/firmware/google/coreboot_table.c | 9 +++++++--
drivers/firmware/google/coreboot_table.h | 1 +
2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
index 9ca21feb9d45..f3694d347801 100644
--- a/drivers/firmware/google/coreboot_table.c
+++ b/drivers/firmware/google/coreboot_table.c
@@ -93,7 +93,12 @@ 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;

@@ -101,7 +106,7 @@ static int coreboot_table_populate(struct device *dev, void *ptr)
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);

ret = device_register(&device->dev);
if (ret) {
diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index beb778674acd..4a89277b99a3 100644
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -66,6 +66,7 @@ struct coreboot_device {
struct coreboot_table_entry entry;
struct lb_cbmem_ref cbmem_ref;
struct lb_framebuffer framebuffer;
+ DECLARE_FLEX_ARRAY(u8, raw);
};
};

--
2.35.1