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Subject[PATCH v11 10/15] arm64: kexec_file: allow for loading Image-format kernel
Date
This patch provides kexec_file_ops for "Image"-format kernel. In this
implementation, a binary is always loaded with a fixed offset identified
in text_offset field of its header.

Regarding signature verification for trusted boot, this patch doesn't
contains CONFIG_KEXEC_VERIFY_SIG support, which is to be added later
in this series, but file-attribute-based verification is still a viable
option by enabling IMA security subsystem.

You can sign(label) a to-be-kexec'ed kernel image on target file system
with:
$ evmctl ima_sign --key /path/to/private_key.pem Image

On live system, you must have IMA enforced with, at least, the following
security policy:
"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig"

See more details about IMA here:
https://sourceforge.net/p/linux-ima/wiki/Home/

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
---
arch/arm64/include/asm/kexec.h | 28 +++++++
arch/arm64/kernel/Makefile | 2 +-
arch/arm64/kernel/kexec_image.c | 108 +++++++++++++++++++++++++
arch/arm64/kernel/machine_kexec_file.c | 1 +
4 files changed, 138 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/kernel/kexec_image.c

diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
index 01bbf6cebf12..69333694e3e2 100644
--- a/arch/arm64/include/asm/kexec.h
+++ b/arch/arm64/include/asm/kexec.h
@@ -101,6 +101,34 @@ struct kimage_arch {
void *dtb_buf;
};

+/**
+ * struct arm64_image_header - arm64 kernel image header
+ * See Documentation/arm64/booting.txt for details
+ *
+ * @mz_magic: DOS header magic number ('MZ', optional)
+ * @code1: Instruction (branch to stext)
+ * @text_offset: Image load offset
+ * @image_size: Effective image size
+ * @flags: Bit-field flags
+ * @reserved: Reserved
+ * @magic: Magic number
+ * @pe_header: Offset to PE COFF header (optional)
+ **/
+
+struct arm64_image_header {
+ __le16 mz_magic; /* also code0 */
+ __le16 pad;
+ __le32 code1;
+ __le64 text_offset;
+ __le64 image_size;
+ __le64 flags;
+ __le64 reserved[3];
+ __le32 magic;
+ __le32 pe_header;
+};
+
+extern const struct kexec_file_ops kexec_image_ops;
+
struct kimage;

extern int load_other_segments(struct kimage *image,
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 06281e1ad7ed..a9cc7752f276 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -50,7 +50,7 @@ arm64-obj-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
arm64-obj-$(CONFIG_HIBERNATION) += hibernate.o hibernate-asm.o
arm64-obj-$(CONFIG_KEXEC_CORE) += machine_kexec.o relocate_kernel.o \
cpu-reset.o
-arm64-obj-$(CONFIG_KEXEC_FILE) += machine_kexec_file.o
+arm64-obj-$(CONFIG_KEXEC_FILE) += machine_kexec_file.o kexec_image.o
arm64-obj-$(CONFIG_ARM64_RELOC_TEST) += arm64-reloc-test.o
arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
new file mode 100644
index 000000000000..a47cf9bc699e
--- /dev/null
+++ b/arch/arm64/kernel/kexec_image.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kexec image loader
+
+ * Copyright (C) 2018 Linaro Limited
+ * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ */
+
+#define pr_fmt(fmt) "kexec_file(Image): " fmt
+
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/kexec.h>
+#include <linux/string.h>
+#include <asm/boot.h>
+#include <asm/byteorder.h>
+#include <asm/cpufeature.h>
+#include <asm/memory.h>
+
+static int image_probe(const char *kernel_buf, unsigned long kernel_len)
+{
+ const struct arm64_image_header *h;
+
+ h = (const struct arm64_image_header *)(kernel_buf);
+
+ if (!h || (kernel_len < sizeof(*h)) ||
+ !memcmp(&h->magic, ARM64_MAGIC, sizeof(ARM64_MAGIC)))
+ return -EINVAL;
+
+ return 0;
+}
+
+static void *image_load(struct kimage *image,
+ char *kernel, unsigned long kernel_len,
+ char *initrd, unsigned long initrd_len,
+ char *cmdline, unsigned long cmdline_len)
+{
+ struct arm64_image_header *h;
+ u64 flags, value;
+ struct kexec_buf kbuf;
+ unsigned long text_offset;
+ struct kexec_segment *kernel_segment;
+ int ret;
+
+ /* Don't support old kernel */
+ h = (struct arm64_image_header *)kernel;
+ if (!h->text_offset)
+ return ERR_PTR(-EINVAL);
+
+ /* Check cpu features */
+ flags = le64_to_cpu(h->flags);
+ value = head_flag_field(flags, HEAD_FLAG_BE);
+ if (((value == HEAD_FLAG_BE) && !IS_ENABLED(CONFIG_CPU_BIG_ENDIAN)) ||
+ ((value != HEAD_FLAG_BE) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN)))
+ if (!system_supports_mixed_endian())
+ return ERR_PTR(-EINVAL);
+
+ value = head_flag_field(flags, HEAD_FLAG_PAGE_SIZE);
+ if (((value == HEAD_FLAG_PAGE_SIZE_4K) &&
+ !system_supports_4kb_granule()) ||
+ ((value == HEAD_FLAG_PAGE_SIZE_64K) &&
+ !system_supports_64kb_granule()) ||
+ ((value == HEAD_FLAG_PAGE_SIZE_16K) &&
+ !system_supports_16kb_granule()))
+ return ERR_PTR(-EINVAL);
+
+ /* Load the kernel */
+ kbuf.image = image;
+ kbuf.buf_min = 0;
+ kbuf.buf_max = ULONG_MAX;
+ kbuf.top_down = false;
+
+ kbuf.buffer = kernel;
+ kbuf.bufsz = kernel_len;
+ kbuf.memsz = le64_to_cpu(h->image_size);
+ text_offset = le64_to_cpu(h->text_offset);
+ kbuf.buf_align = SZ_2M;
+
+ /* Adjust kernel segment with TEXT_OFFSET */
+ kbuf.memsz += text_offset;
+
+ ret = kexec_add_buffer(&kbuf);
+ if (ret)
+ goto out;
+
+ kernel_segment = &image->segment[image->nr_segments - 1];
+ kernel_segment->mem += text_offset;
+ kernel_segment->memsz -= text_offset;
+ image->start = kernel_segment->mem;
+
+ pr_debug("Loaded kernel at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
+ kernel_segment->mem, kbuf.bufsz,
+ kernel_segment->memsz);
+
+ /* Load additional data */
+ ret = load_other_segments(image,
+ kernel_segment->mem, kernel_segment->memsz,
+ initrd, initrd_len, cmdline, cmdline_len);
+
+out:
+ return ERR_PTR(ret);
+}
+
+const struct kexec_file_ops kexec_image_ops = {
+ .probe = image_probe,
+ .load = image_load,
+};
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index ca00681c25c6..a0b44fe18b95 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -20,6 +20,7 @@
#include <asm/byteorder.h>

const struct kexec_file_ops * const kexec_file_loaders[] = {
+ &kexec_image_ops,
NULL
};

--
2.17.0
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