[PATCH v3] firmware: coreboot: Check size of table entry and split memcpy

[PATCH v3] firmware: coreboot: Check size of table entry and split memcpy

[Kees Cook]

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
---
v3: leave memcpy source as ptr_entry (jwerner)
v2: https://lore.kernel.org/lkml/20230107031406.gonna.761-kees@kernel.org
v1: https://lore.kernel.org/lkml/20230106045327.never.413-kees@kernel.org
---
 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 2652c396c423..33ae94745aef 100644
--- 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 37f4d335a606..d814dca33a08 100644
--- 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);
 	};
 };
 
-- 
2.34.1

Re: [PATCH v3] firmware: coreboot: Check size of table entry and split memcpy

[Stephen Boyd]

Quoting Kees Cook (2023-01-12 15:03:16)
> 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>

Re: [PATCH v3] firmware: coreboot: Check size of table entry and split memcpy

[Jack Rosenthal]

On 2023-01-12 at 15:03 -0800, Kees Cook wrote:
> 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: Jack Rosenthal <jrosenth@chromium.org>