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efi: add ovmf debug log driver 

Recent OVMF versions (edk2-stable202508 + newer) can write their debug
log to a memory buffer.  This driver exposes the log content via sysfs
(/sys/firmware/efi/ovmf_debug_log).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Gerd Hoffmann 2025-07-08 14:56:23 +02:00 committed by Ard Biesheuvel
parent 19272b37aa
commit f393a76176
5 changed files with 132 additions and 0 deletions
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8
drivers/firmware/efi/Kconfig
View File

@ -263,6 +263,14 @@ config EFI_COCO_SECRET
virt/coco/efi_secret module to access the secrets, which in turn
allows userspace programs to access the injected secrets.
config OVMF_DEBUG_LOG
bool "Expose OVMF firmware debug log via sysfs"
depends on EFI
help
Recent OVMF versions (edk2-stable202508 + newer) can write
their debug log to a memory buffer. This driver exposes the
log content via sysfs (/sys/firmware/efi/ovmf_debug_log).
config UNACCEPTED_MEMORY
bool
depends on EFI_STUB

1
drivers/firmware/efi/Makefile
View File

@ -29,6 +29,7 @@ obj-$(CONFIG_APPLE_PROPERTIES) += apple-properties.o
obj-$(CONFIG_EFI_RCI2_TABLE) += rci2-table.o
obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE) += embedded-firmware.o
obj-$(CONFIG_LOAD_UEFI_KEYS) += mokvar-table.o
obj-$(CONFIG_OVMF_DEBUG_LOG) += ovmf-debug-log.o
obj-$(CONFIG_SYSFB) += sysfb_efi.o

8
drivers/firmware/efi/efi.c
View File

@ -45,6 +45,7 @@ struct efi __read_mostly efi = {
.esrt = EFI_INVALID_TABLE_ADDR,
.tpm_log = EFI_INVALID_TABLE_ADDR,
.tpm_final_log = EFI_INVALID_TABLE_ADDR,
.ovmf_debug_log = EFI_INVALID_TABLE_ADDR,
#ifdef CONFIG_LOAD_UEFI_KEYS
.mokvar_table = EFI_INVALID_TABLE_ADDR,
#endif
@ -473,6 +474,10 @@ static int __init efisubsys_init(void)
platform_device_register_simple("efi_secret", 0, NULL, 0);
#endif
if (IS_ENABLED(CONFIG_OVMF_DEBUG_LOG) &&
efi.ovmf_debug_log != EFI_INVALID_TABLE_ADDR)
ovmf_log_probe(efi.ovmf_debug_log);
return 0;
err_remove_group:
@ -617,6 +622,9 @@ static const efi_config_table_type_t common_tables[] __initconst = {
{LINUX_EFI_MEMRESERVE_TABLE_GUID, &mem_reserve, "MEMRESERVE" },
{LINUX_EFI_INITRD_MEDIA_GUID, &initrd, "INITRD" },
{EFI_RT_PROPERTIES_TABLE_GUID, &rt_prop, "RTPROP" },
#ifdef CONFIG_OVMF_DEBUG_LOG
{OVMF_MEMORY_LOG_TABLE_GUID, &efi.ovmf_debug_log, "OvmfDebugLog" },
#endif
#ifdef CONFIG_EFI_RCI2_TABLE
{DELLEMC_EFI_RCI2_TABLE_GUID, &rci2_table_phys },
#endif

111
drivers/firmware/efi/ovmf-debug-log.c Normal file
View File

@ -0,0 +1,111 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/efi.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/sysfs.h>
#define OVMF_DEBUG_LOG_MAGIC1 0x3167646d666d766f // "ovmfmdg1"
#define OVMF_DEBUG_LOG_MAGIC2 0x3267646d666d766f // "ovmfmdg2"
struct ovmf_debug_log_header {
u64 magic1;
u64 magic2;
u64 hdr_size;
u64 log_size;
u64 lock; // edk2 spinlock
u64 head_off;
u64 tail_off;
u64 truncated;
u8 fw_version[128];
};
static struct ovmf_debug_log_header *hdr;
static u8 *logbuf;
static u64 logbufsize;
static ssize_t ovmf_log_read(struct file *filp, struct kobject *kobj,
const struct bin_attribute *attr, char *buf,
loff_t offset, size_t count)
{
u64 start, end;
start = hdr->head_off + offset;
if (hdr->head_off > hdr->tail_off && start >= hdr->log_size)
start -= hdr->log_size;
end = start + count;
if (start > hdr->tail_off) {
if (end > hdr->log_size)
end = hdr->log_size;
} else {
if (end > hdr->tail_off)
end = hdr->tail_off;
}
if (start > logbufsize || end > logbufsize)
return 0;
if (start >= end)
return 0;
memcpy(buf, logbuf + start, end - start);
return end - start;
}
static struct bin_attribute ovmf_log_bin_attr = {
.attr = {
.name = "ovmf_debug_log",
.mode = 0444,
},
.read = ovmf_log_read,
};
int __init ovmf_log_probe(unsigned long ovmf_debug_log_table)
{
int ret = -EINVAL;
u64 size;
/* map + verify header */
hdr = memremap(ovmf_debug_log_table, sizeof(*hdr), MEMREMAP_WB);
if (!hdr) {
pr_err("OVMF debug log: header map failed\n");
return -EINVAL;
}
if (hdr->magic1 != OVMF_DEBUG_LOG_MAGIC1 ||
hdr->magic2 != OVMF_DEBUG_LOG_MAGIC2) {
printk(KERN_ERR "OVMF debug log: magic mismatch\n");
goto err_unmap;
}
size = hdr->hdr_size + hdr->log_size;
pr_info("OVMF debug log: firmware version: \"%s\"\n", hdr->fw_version);
pr_info("OVMF debug log: buffer size: %lluk\n", size / 1024);
/* map complete log buffer */
memunmap(hdr);
hdr = memremap(ovmf_debug_log_table, size, MEMREMAP_WB);
if (!hdr) {
pr_err("OVMF debug log: buffer map failed\n");
return -EINVAL;
}
logbuf = (void *)hdr + hdr->hdr_size;
logbufsize = hdr->log_size;
ovmf_log_bin_attr.size = size;
ret = sysfs_create_bin_file(efi_kobj, &ovmf_log_bin_attr);
if (ret != 0) {
pr_err("OVMF debug log: sysfs register failed\n");
goto err_unmap;
}
return 0;
err_unmap:
memunmap(hdr);
return ret;
}

4
include/linux/efi.h
View File

@ -439,6 +439,7 @@ void efi_native_runtime_setup(void);
/* OVMF protocol GUIDs */
#define OVMF_SEV_MEMORY_ACCEPTANCE_PROTOCOL_GUID EFI_GUID(0xc5a010fe, 0x38a7, 0x4531, 0x8a, 0x4a, 0x05, 0x00, 0xd2, 0xfd, 0x16, 0x49)
#define OVMF_MEMORY_LOG_TABLE_GUID EFI_GUID(0x95305139, 0xb20f, 0x4723, 0x84, 0x25, 0x62, 0x7c, 0x88, 0x8f, 0xf1, 0x21)
typedef struct {
efi_guid_t guid;
@ -642,6 +643,7 @@ extern struct efi {
unsigned long esrt; /* ESRT table */
unsigned long tpm_log; /* TPM2 Event Log table */
unsigned long tpm_final_log; /* TPM2 Final Events Log table */
unsigned long ovmf_debug_log;
unsigned long mokvar_table; /* MOK variable config table */
unsigned long coco_secret; /* Confidential computing secret table */
unsigned long unaccepted; /* Unaccepted memory table */
@ -1344,6 +1346,8 @@ bool efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table)
umode_t efi_attr_is_visible(struct kobject *kobj, struct attribute *attr, int n);
int ovmf_log_probe(unsigned long ovmf_debug_log_table);
/*
* efivar ops event type
*/