efi: add ovmf debug log driver (f393a761) · Commits · git / linux-nf

drivers/firmware/efi/Kconfig

+8 −0

Original line number	Diff line number	Diff line
		@@ -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

drivers/firmware/efi/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -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

drivers/firmware/efi/efi.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -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

drivers/firmware/efi/ovmf-debug-log.c

0 → 100644

+111 −0

Original line number	Diff line number	Diff line
		// 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;
		}

include/linux/efi.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -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
		*/