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firmware: coreboot: Check size of table entry and split memcpy

PATCH In review Kees Cook 3 participants 3 messages Jan 12, 2023 – Jan 13, 2023

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Kees Cook

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#0 lore raw

PATCH v3 1/1 firmware: coreboot: Check size of table entry and split memcpy

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 <[email protected]>
Link https://lore.kernel.org/all/[email protected]/ open here
Cc Jack Rosenthal <[email protected]>
Cc Guenter Roeck <[email protected]>
Cc Julius Werner <[email protected]>
Cc Brian Norris <[email protected]>
Cc Stephen Boyd <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Signed-off-by Kees Cook <[email protected]>
Reviewed-by Julius Werner <[email protected]>
Reviewed-by Guenter Roeck <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here

---
v3: leave memcpy source as ptr_entry (jwerner)
v2: https://lore.kernel.org/lkml/[email protected]
v1: https://lore.kernel.org/lkml/[email protected]

---
 drivers/firmware/google/coreboot_table.c | 9 +++++++--
 drivers/firmware/google/coreboot_table.h | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)
drivers/firmware/google/coreboot_table.c +7 -2
index 2652c396c423..33ae94745aef 100644
@@ -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:
drivers/firmware/google/coreboot_table.h +1 -0
index 37f4d335a606..d814dca33a08 100644
@@ -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);
 	};
 };
Signature · 1 line
2.34.1
Reviewed-by on v3 1/1
#1 lore raw

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

Quoted 21 lines

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 <[email protected]>
Link https://lore.kernel.org/all/[email protected]/ open here
Cc Jack Rosenthal <[email protected]>
Cc Guenter Roeck <[email protected]>
Cc Julius Werner <[email protected]>
Cc Brian Norris <[email protected]>
Cc Stephen Boyd <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Signed-off-by Kees Cook <[email protected]>
Reviewed-by Julius Werner <[email protected]>
Reviewed-by Guenter Roeck <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Quoted 1 line

---

Reviewed-by Stephen Boyd <[email protected]>
Reviewed-by on v3 1/1
#2 lore raw
In reply to Kees Cook
Quoted 21 lines · 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 <[email protected]>
Link https://lore.kernel.org/all/[email protected]/ open here
Cc Jack Rosenthal <[email protected]>
Cc Guenter Roeck <[email protected]>
Cc Julius Werner <[email protected]>
Cc Brian Norris <[email protected]>
Cc Stephen Boyd <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Signed-off-by Kees Cook <[email protected]>
Reviewed-by Julius Werner <[email protected]>
Reviewed-by Guenter Roeck <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Quoted 1 line

---

Reviewed-by Jack Rosenthal <[email protected]>