Re: [PATCH v4] x86/kexec: Carry forward IMA measurement log on kexec

From: Lakshmi Ramasubramanian
Date: Fri May 13 2022 - 13:19:38 EST

Hi Jonathan,

On 5/12/2022 9:25 AM, Jonathan McDowell wrote:
On kexec file load Integrity Measurement Architecture (IMA) subsystem
may verify the IMA signature of the kernel and initramfs, and measure
it. The command line parameters passed to the kernel in the kexec call
may also be measured by IMA. A remote attestation service can verify
a TPM quote based on the TPM event log, the IMA measurement list, and
the TPM PCR data. This can be achieved only if the IMA measurement log
is carried over from the current kernel to the next kernel across
the kexec call.

powerpc and ARM64 both achieve this using device tree with a
"linux,ima-kexec-buffer" node. x86 platforms generally don't make use of
device tree, so use the setup_data mechanism to pass the IMA buffer to
the new kernel.

Signed-off-by: Jonathan McDowell <noodles@xxxxxx>
---
v4:
- Guard ima.h function prototypes with CONFIG_HAVE_IMA_KEXEC
v3:
- Rebase on tip/master
- Pull ima_(free|get)_kexec_buffer into x86 code
- Push ifdefs into functions where possible
- Reverse fir tree variable declarations
- Fix section annotation on ima_free_kexec_buffer (__meminit)
- Only allocate ima_setup_data space when IMA_KEXEC is enabled
v2:
- Fix operation with EFI systems
---
arch/x86/Kconfig | 1 +
arch/x86/include/uapi/asm/bootparam.h | 9 ++++
arch/x86/kernel/e820.c | 6 +--
arch/x86/kernel/kexec-bzimage64.c | 38 ++++++++++++++++
arch/x86/kernel/setup.c | 62 +++++++++++++++++++++++++++
drivers/of/kexec.c | 1 +
include/linux/ima.h | 5 +++
include/linux/of.h | 2 -
security/integrity/ima/ima_kexec.c | 2 +-
9 files changed, 120 insertions(+), 6 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f1320d9a3da3..594636f02da4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2027,6 +2027,7 @@ config KEXEC_FILE
bool "kexec file based system call"
select KEXEC_CORE
select BUILD_BIN2C
+ select HAVE_IMA_KEXEC if IMA
depends on X86_64
depends on CRYPTO=y
depends on CRYPTO_SHA256=y
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index bea5cdcdf532..ca0796ac4403 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -11,6 +11,7 @@
#define SETUP_APPLE_PROPERTIES 5
#define SETUP_JAILHOUSE 6
#define SETUP_CC_BLOB 7
+#define SETUP_IMA 8
#define SETUP_INDIRECT (1<<31)
@@ -172,6 +173,14 @@ struct jailhouse_setup_data {
} __attribute__((packed)) v2;
} __attribute__((packed));
+/*
+ * IMA buffer setup data information from the previous kernel during kexec
+ */
+struct ima_setup_data {
+ __u64 addr;
+ __u64 size;
+} __attribute__((packed));
+
/* The so-called "zeropage" */
struct boot_params {
struct screen_info screen_info; /* 0x000 */
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index f267205f2d5a..9dac24680ff8 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1017,10 +1017,10 @@ void __init e820__reserve_setup_data(void)
e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
/*
- * SETUP_EFI is supplied by kexec and does not need to be
- * reserved.
+ * SETUP_EFI and SETUP_IMA are supplied by kexec and do not need
+ * to be reserved.
*/
- if (data->type != SETUP_EFI)
+ if (data->type != SETUP_EFI && data->type != SETUP_IMA)
e820__range_update_kexec(pa_data,
sizeof(*data) + data->len,
E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index 170d0fd68b1f..54bd4ce5f908 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -186,6 +186,33 @@ setup_efi_state(struct boot_params *params, unsigned long params_load_addr,
}
#endif /* CONFIG_EFI */
+static void
+setup_ima_state(const struct kimage *image, struct boot_params *params,
+ unsigned long params_load_addr,
+ unsigned int ima_setup_data_offset)
+{
+#ifdef CONFIG_IMA_KEXEC
+ struct setup_data *sd = (void *)params + ima_setup_data_offset;
+ unsigned long setup_data_phys;
+ struct ima_setup_data *ima;
+
+ if (!image->ima_buffer_size)
+ return;
+
+ sd->type = SETUP_IMA;
+ sd->len = sizeof(*ima);
+
+ ima = (void *)sd + sizeof(struct setup_data);
+ ima->addr = image->ima_buffer_addr;
+ ima->size = image->ima_buffer_size;
+
+ /* Add setup data */
+ setup_data_phys = params_load_addr + ima_setup_data_offset;
+ sd->next = params->hdr.setup_data;
+ params->hdr.setup_data = setup_data_phys;
+#endif /* CONFIG_IMA_KEXEC */
+}
+
static int
setup_boot_parameters(struct kimage *image, struct boot_params *params,
unsigned long params_load_addr,
@@ -247,6 +274,13 @@ setup_boot_parameters(struct kimage *image, struct boot_params *params,
setup_efi_state(params, params_load_addr, efi_map_offset, efi_map_sz,
efi_setup_data_offset);
#endif
+
+ /* Setup IMA log buffer state */
+ setup_ima_state(image, params, params_load_addr,
+ efi_setup_data_offset +
+ sizeof(struct setup_data) +
+ sizeof(struct efi_setup_data));
Here you could check image->ima_buffer_size and call setup_ima_state() only if it is non-zero.

+
/* Setup EDD info */
memcpy(params->eddbuf, boot_params.eddbuf,
EDDMAXNR * sizeof(struct edd_info));
@@ -403,6 +437,10 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
sizeof(struct setup_data) +
sizeof(struct efi_setup_data);
+ if (IS_ENABLED(CONFIG_IMA_KEXEC))
+ kbuf.bufsz += sizeof(struct setup_data) +
+ sizeof(struct ima_setup_data);
+
params = kzalloc(kbuf.bufsz, GFP_KERNEL);
if (!params)
return ERR_PTR(-ENOMEM);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 249981bf3d8a..ab5e7a351845 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -11,6 +11,7 @@
#include <linux/dma-map-ops.h>
#include <linux/dmi.h>
#include <linux/efi.h>
+#include <linux/ima.h>
#include <linux/init_ohci1394_dma.h>
#include <linux/initrd.h>
#include <linux/iscsi_ibft.h>
@@ -145,6 +146,11 @@ __visible unsigned long mmu_cr4_features __ro_after_init;
__visible unsigned long mmu_cr4_features __ro_after_init = X86_CR4_PAE;
#endif
+#ifdef CONFIG_IMA
+static phys_addr_t ima_kexec_buffer_phys;
+static size_t ima_kexec_buffer_size;
+#endif
+
/* Boot loader ID and version as integers, for the benefit of proc_dointvec */
int bootloader_type, bootloader_version;
@@ -335,6 +341,59 @@ static void __init reserve_initrd(void)
}
#endif /* CONFIG_BLK_DEV_INITRD */
+static void __init add_early_ima_buffer(u64 phys_addr)
+{
+#ifdef CONFIG_IMA
+ struct ima_setup_data *data;
+
+ data = early_memremap(phys_addr + sizeof(struct setup_data),
+ sizeof(*data));
+ if (!data) {
+ pr_warn("setup: failed to memremap ima_setup_data entry\n");
+ return;
+ }
Here if memory allocation fails, would kexec system call fail or would it only not add IMA buffer, but continue with the system call?

+ if (data->size != 0) {
+ memblock_reserve(data->addr, data->size);
+ ima_kexec_buffer_phys = data->addr;
+ ima_kexec_buffer_size = data->size;
+ }
+ early_memunmap(data, sizeof(*data));
+#else
+ pr_warn("Passed IMA kexec data, but CONFIG_IMA not set. Ignoring.\n");
Is this warning message useful? Can we just inline (NOP) this function if CONFIG_IMA is not set?

+#endif
+}
+
+#if defined(CONFIG_IMA) && !defined(CONFIG_OF_FLATTREE)
+int __meminit ima_free_kexec_buffer(void)
+{
ima_free_kexec_buffer() should be invoked if the previous kernel had passed the IMA buffer (i.e., CONFIG_HAVE_IMA_KEXEC is set). CONFIG_HAVE_IMA_KEXEC would be set only if CONFIG_IMA is set. Is the above check still required?

thanks,
-lakshmi

+ int rc;
+
+ if (ima_kexec_buffer_size == 0)
+ return -ENOENT;
+
+ rc = memblock_phys_free(ima_kexec_buffer_phys,
+ ima_kexec_buffer_size);
+ if (rc)
+ return rc;
+
+ ima_kexec_buffer_phys = 0;
+ ima_kexec_buffer_size = 0;
+
+ return 0;
+}
+
+int __init ima_get_kexec_buffer(void **addr, size_t *size)
+{
+ if (ima_kexec_buffer_size == 0)
+ return -ENOENT;
+
+ *addr = __va(ima_kexec_buffer_phys);
+ *size = ima_kexec_buffer_size;
+
+ return 0;
+}
+#endif
+
static void __init parse_setup_data(void)
{
struct setup_data *data;
@@ -360,6 +419,9 @@ static void __init parse_setup_data(void)
case SETUP_EFI:
parse_efi_setup(pa_data, data_len);
break;
+ case SETUP_IMA:
+ add_early_ima_buffer(pa_data);
+ break;
default:
break;
}
diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
index b9bd1cff1793..74fdd490f7c0 100644
--- a/drivers/of/kexec.c
+++ b/drivers/of/kexec.c
@@ -9,6 +9,7 @@
* Copyright (C) 2016 IBM Corporation
*/
+#include <linux/ima.h>
#include <linux/kernel.h>
#include <linux/kexec.h>
#include <linux/memblock.h>
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 426b1744215e..ff4bd993e432 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -140,6 +140,11 @@ static inline int ima_measure_critical_data(const char *event_label,
#endif /* CONFIG_IMA */
+#ifdef CONFIG_HAVE_IMA_KEXEC
+int ima_free_kexec_buffer(void);
+int ima_get_kexec_buffer(void **addr, size_t *size);
+#endif
+
#ifdef CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT
extern bool arch_ima_get_secureboot(void);
extern const char * const *arch_get_ima_policy(void);
diff --git a/include/linux/of.h b/include/linux/of.h
index 04971e85fbc9..c2f58d2e3a0e 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -441,8 +441,6 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
unsigned long initrd_load_addr,
unsigned long initrd_len,
const char *cmdline, size_t extra_fdt_size);
-int ima_get_kexec_buffer(void **addr, size_t *size);
-int ima_free_kexec_buffer(void);
#else /* CONFIG_OF */
static inline void of_core_init(void)
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 13753136f03f..419dc405c831 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -137,7 +137,7 @@ void ima_add_kexec_buffer(struct kimage *image)
/*
* Restore the measurement list from the previous kernel.
*/
-void ima_load_kexec_buffer(void)
+void __init ima_load_kexec_buffer(void)
{
void *kexec_buffer = NULL;
size_t kexec_buffer_size = 0;