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firmware: coreboot: Skip no-map CBMEM entries

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On ARM64 platforms, certain reserved memory regions (like those used
by pKVM) are marked with the 'no-map' property. This indicates that
the host kernel is forbidden from creating a structural mapping for
these regions.

The coreboot table may describe CBMEM entries that overlap with or are
entirely contained within these no-map regions. Attempting to populate
these entries as devices and subsequently remapping them can lead to
system crashes or security violations.

Refine the coreboot table population logic to verify that each CBMEM
entry resides in 'Known Good' memory before creating a device. An
entry is only considered safe if it is entirely System RAM or entirely
standard Reserved memory (tagged with IORES_DESC_RESERVED).

This dual-check ensures that:
1. On ARM64, no-map regions are filtered out as they are IORESOURCE_MEM
   (see request_standard_resources() in arch/arm64/kernel/setup.c).
2. On x86, standard reserved regions (IORES_DESC_RESERVED) remain
   supported.

Signed-off-by: Yidi Lin <yidilin@google.com>
Signed-off-by: Hsin-Te Yuan <yuanhsinte@chromium.org>
Link: https://lore.kernel.org/r/20260717-coreboot-v2-1-8f8b389e3758@chromium.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
This commit is contained in:
Yidi Lin 2026-07-17 08:41:26 +00:00 committed by Tzung-Bi Shih
parent 65a9b9b2de
commit e31ecda9e3
1 changed files with 23 additions and 3 deletions
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26
drivers/firmware/google/coreboot_table.c
View File

@ -13,8 +13,10 @@
#include <linux/err.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/device-id/coreboot.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
@ -123,7 +125,7 @@ static int coreboot_table_populate(struct device *dev, void *ptr, resource_size_
ptr_end = ptr + len;
ptr_entry = ptr + header->header_bytes;
for (i = 0; i < header->table_entries; i++) {
for (i = 0; i < header->table_entries; i++, ptr_entry += entry->size) {
if (ptr_entry + sizeof(*entry) > ptr_end)
return -EINVAL;
entry = ptr_entry;
@ -147,6 +149,26 @@ static int coreboot_table_populate(struct device *dev, void *ptr, resource_size_
switch (device->entry.tag) {
case LB_TAG_CBMEM_ENTRY:
/*
* Skip entries that are not exclusively System RAM or
* Reserved memory.
* On ARM64, no-map regions are filtered out as they are
* IORESOURCE_MEM (see request_standard_resources() in
* arch/arm64/kernel/setup.c).
* On x86, CBMEM often resides in standard reserved regions
* (IORES_DESC_RESERVED).
*/
if (region_intersects(device->cbmem_entry.address,
device->cbmem_entry.entry_size,
IORESOURCE_SYSTEM_RAM,
IORES_DESC_NONE) != REGION_INTERSECTS &&
region_intersects(device->cbmem_entry.address,
device->cbmem_entry.entry_size,
IORESOURCE_MEM,
IORES_DESC_RESERVED) != REGION_INTERSECTS) {
kfree(device);
continue;
}
dev_set_name(&device->dev, "cbmem-%08x",
device->cbmem_entry.id);
break;
@ -155,8 +177,6 @@ static int coreboot_table_populate(struct device *dev, void *ptr, resource_size_
break;
}
ptr_entry += entry->size;
ret = device_register(&device->dev);
if (ret) {
dev_warn(dev, "failed to register coreboot device: %d\n", ret);