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Re: [PATCH 13/14] arm64: kexec_file: add Image format support

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On Thu, Aug 24, 2017 at 05:18:10PM +0900, AKASHI Takahiro wrote:
> The "Image" binary will be loaded at the offset of TEXT_OFFSET from
> the start of system memory. TEXT_OFFSET is basically determined from
> the header of the image.

What's the policy for the binary types kexec_file_load() will load, and
how are these identified? AFAICT, there are no flags, so it looks like
we're just checking the magic and hoping.

> Regarding kernel verification, it will be done through
> verify_pefile_signature() as arm64's "Image" binary can be seen as
> in PE format. This approach is consistent with x86 implementation.

This will not work for kernels built without CONFIG_EFI, where we don't
have a PE header.

What happens in that case?

[...]

> +/**
> + * arm64_header_check_msb - Helper to check the arm64 image header.
> + *
> + * Returns non-zero if the image was built as big endian.
> + */
> +
> +static inline int arm64_header_check_msb(const struct arm64_image_header *h)
> +{
> +	if (!h)
> +		return 0;
> +
> +	return !!(h->flags[7] & arm64_image_flag_7_be);
> +}

What are we going to use this for?

In kernel, we use the term "BE" rather than "MSB", and it's unfortunate
to have code with varying naming conventions.

[...]

> +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 kexec_buf kbuf;
> +	struct arm64_image_header *h = (struct arm64_image_header *)kernel;
> +	unsigned long text_offset, kernel_load_addr;
> +	int ret;
> +
> +	/* Create elf core header segment */
> +	ret = load_crashdump_segments(image);
> +	if (ret)
> +		goto out;
> +
> +	/* Load the kernel */
> +	kbuf.image = image;
> +	if (image->type == KEXEC_TYPE_CRASH) {
> +		kbuf.buf_min = crashk_res.start;
> +		kbuf.buf_max = crashk_res.end + 1;
> +	} else {
> +		kbuf.buf_min = 0;
> +		kbuf.buf_max = ULONG_MAX;
> +	}
> +	kbuf.top_down = 0;
> +
> +	kbuf.buffer = kernel;
> +	kbuf.bufsz = kernel_len;
> +	if (h->image_size) {
> +		kbuf.memsz = le64_to_cpu(h->image_size);
> +		text_offset = le64_to_cpu(h->text_offset);
> +	} else {
> +		/* v3.16 or older */
> +		kbuf.memsz = kbuf.bufsz; /* NOTE: not including BSS */

Why bother supporting < 3.16 kernels?

They predate regulate kexec, we know we don't have enough information to
boot such kernels reliably, and arguably attempting to load one would
indicate some kind of rollback attack.

Thanks,
Mark.

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[PATCH 00/14] arm64: kexec: add kexec_file_load support AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:20 +0200
  [PATCH 14/14] arm64: kexec_file: add vmlinux format support AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:20 +0200
    Re: [PATCH 14/14] arm64: kexec_file: add vmlinux format support Mark Rutland <mark.rutland@arm.com> - 2017-08-24 19:40 +0200
      Re: [PATCH 14/14] arm64: kexec_file: add vmlinux format support AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 04:10 +0200
        Re: [PATCH 14/14] arm64: kexec_file: add vmlinux format support Dave Young <dyoung@redhat.com> - 2017-08-25 08:20 +0200
  [PATCH 08/14] arm64: kexec_file: create purgatory AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:20 +0200
    Re: [PATCH 08/14] arm64: kexec_file: create purgatory Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-08-24 11:20 +0200
      Re: [PATCH 08/14] arm64: kexec_file: create purgatory AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 03:20 +0200
    Re: [PATCH 08/14] arm64: kexec_file: create purgatory Mark Rutland <mark.rutland@arm.com> - 2017-08-24 19:00 +0200
      Re: [PATCH 08/14] arm64: kexec_file: create purgatory AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 03:10 +0200
        Re: [PATCH 08/14] arm64: kexec_file: create purgatory Mark Rutland <mark.rutland@arm.com> - 2017-08-25 12:30 +0200
  [PATCH 02/14] include: pe.h: remove message[] from mz header definition AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:20 +0200
    Re: [PATCH 02/14] include: pe.h: remove message[] from mz header definition Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-08-24 11:10 +0200
  [PATCH 01/14] MODSIGN: Export module signature definitions AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:20 +0200
  [PATCH 09/14] arm64: kexec_file: add sha256 digest check in purgatory AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
    Re: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in purgatory Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-08-24 11:20 +0200
      Re: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in  purgatory AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 03:30 +0200
    Re: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in  purgatory Mark Rutland <mark.rutland@arm.com> - 2017-08-24 19:10 +0200
      Re: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in  purgatory AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 03:30 +0200
        Re: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in  purgatory Mark Rutland <mark.rutland@arm.com> - 2017-08-25 12:50 +0200
  [PATCH 07/14] asm-generic: add kexec_file_load system call to unistd.h AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
    Re: [PATCH 07/14] asm-generic: add kexec_file_load system call to unistd.h Arnd Bergmann <arnd@arndb.de> - 2017-08-24 13:00 +0200
  [PATCH 13/14] arm64: kexec_file: add Image format support AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
    Re: [PATCH 13/14] arm64: kexec_file: add Image format support Mark Rutland <mark.rutland@arm.com> - 2017-08-24 19:30 +0200
      Re: [PATCH 13/14] arm64: kexec_file: add Image format support AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 04:00 +0200
  [PATCH 03/14] resource: add walk_system_ram_res_rev() AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
    Re: [PATCH 03/14] resource: add walk_system_ram_res_rev() Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-08-24 11:10 +0200
      Re: [PATCH 03/14] resource: add walk_system_ram_res_rev() AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 03:00 +0200
  [PATCH 10/14] arm64: kexec_file: load initrd, device-tree and purgatory segments AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
    Re: [PATCH 10/14] arm64: kexec_file: load initrd, device-tree and  purgatory segments Mark Rutland <mark.rutland@arm.com> - 2017-08-24 19:20 +0200
      Re: [PATCH 10/14] arm64: kexec_file: load initrd, device-tree and  purgatory segments AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-25 03:40 +0200
  [PATCH 04/14] kexec_file: factor out vmlinux (elf) parser from powerpc AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
  [PATCH 05/14] kexec_file: factor out crashdump elf header function from x86 AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
    Re: [PATCH 05/14] kexec_file: factor out crashdump elf header  function from x86 Dave Young <dyoung@redhat.com> - 2017-08-25 07:50 +0200
  [PATCH 06/14] kexec_file: add kexec_add_segment() AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
  [PATCH 12/14] arm64: enable KEXEC_FILE config AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200
  [PATCH 11/14] arm64: kexec_file: set up for crash dump adding elf core header AKASHI Takahiro <takahiro.akashi@linaro.org> - 2017-08-24 10:30 +0200

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