[PATCH v2 3/6] kexec_file: Allow skipping checksum calculation for some segments.
Dave Young
dyoung at redhat.com
Sun Aug 21 20:17:45 PDT 2016
On 08/18/16 at 06:09pm, Thiago Jung Bauermann wrote:
> Hello Dave,
>
> Thanks for your review!
>
> [ Trimming down Cc: list a little to try to clear the "too many recipients"
> mailing list restriction. ]
I also got "too many recipients".. Thanks for the trimming.
>
> Am Donnerstag, 18 August 2016, 17:03:30 schrieb Dave Young:
> > On 08/13/16 at 12:18am, Thiago Jung Bauermann wrote:
> > > Adds checksum argument to kexec_add_buffer specifying whether the given
> > > segment should be part of the checksum calculation.
> >
> > Since it is used with add buffer, could it be added to kbuf as a new
> > field?
>
> I was on the fence about adding it as a new argument to kexec_add_buffer or
> as a new field to struct kexec_buf. Both alternatives make sense to me. I
> implemented your suggestion in the patch below, what do you think?
>
> > Like kbuf.no_checksum, default value is 0 that means checksum is needed
> > if it is 1 then no need a checksum.
>
> It's an interesting idea and I implemented it that way, though in practice
> all current users of struct kexec_buf put it on the stack so the field needs
> to be initialized explicitly.
>
> --
> []'s
> Thiago Jung Bauermann
> IBM Linux Technology Center
>
>
> Subject: [PATCH v2 3/6] kexec_file: Allow skipping checksum calculation for
> some segments.
>
> Add skip_checksum member to struct kexec_buf to specify whether the
> corresponding segment should be part of the checksum calculation.
>
> The next patch will add a way to update segments after a kimage is loaded.
> Segments that will be updated in this way should not be checksummed,
> otherwise they will cause the purgatory checksum verification to fail
> when the machine is rebooted.
>
> As a bonus, we don't need to special-case the purgatory segment anymore
> to avoid checksumming it.
>
> Adjust places using struct kexec_buf to set skip_checksum.
>
> Signed-off-by: Thiago Jung Bauermann <bauerman at linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/kexec_elf_64.c | 5 +++--
> arch/x86/kernel/crash.c | 3 ++-
> arch/x86/kernel/kexec-bzimage64.c | 2 +-
> include/linux/kexec.h | 23 ++++++++++++++---------
> kernel/kexec_file.c | 15 +++++++--------
> 5 files changed, 27 insertions(+), 21 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kexec_elf_64.c b/arch/powerpc/kernel/kexec_elf_64.c
> index 22afc7b5ee73..d009f5363968 100644
> --- a/arch/powerpc/kernel/kexec_elf_64.c
> +++ b/arch/powerpc/kernel/kexec_elf_64.c
> @@ -107,7 +107,7 @@ static int elf_exec_load(struct kimage *image, struct elfhdr *ehdr,
> int ret;
> size_t i;
> struct kexec_buf kbuf = { .image = image, .buf_max = ppc64_rma_size,
> - .top_down = false };
> + .top_down = false, .skip_checksum = false };
No need to set it as false because it will be initialized to 0 by
default?
>
> /* Read in the PT_LOAD segments. */
> for (i = 0; i < ehdr->e_phnum; i++) {
> @@ -162,7 +162,8 @@ void *elf64_load(struct kimage *image, char *kernel_buf,
> struct elf_info elf_info;
> struct fdt_reserve_entry *rsvmap;
> struct kexec_buf kbuf = { .image = image, .buf_min = 0,
> - .buf_max = ppc64_rma_size };
> + .buf_max = ppc64_rma_size,
> + .skip_checksum = false };
>
> ret = build_elf_exec_info(kernel_buf, kernel_len, &ehdr, &elf_info);
> if (ret)
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 38a1cdf6aa05..7b8f62c86651 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -617,7 +617,8 @@ int crash_load_segments(struct kimage *image)
> {
> int ret;
> struct kexec_buf kbuf = { .image = image, .buf_min = 0,
> - .buf_max = ULONG_MAX, .top_down = false };
> + .buf_max = ULONG_MAX, .top_down = false,
> + .skip_checksum = false };
>
> /*
> * Determine and load a segment for backup area. First 640K RAM
> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
> index 4b3a75329fb6..449f433cd225 100644
> --- a/arch/x86/kernel/kexec-bzimage64.c
> +++ b/arch/x86/kernel/kexec-bzimage64.c
> @@ -341,7 +341,7 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
> unsigned int setup_hdr_offset = offsetof(struct boot_params, hdr);
> unsigned int efi_map_offset, efi_map_sz, efi_setup_data_offset;
> struct kexec_buf kbuf = { .image = image, .buf_max = ULONG_MAX,
> - .top_down = true };
> + .top_down = true, .skip_checksum = false };
>
> header = (struct setup_header *)(kernel + setup_hdr_offset);
> setup_sects = header->setup_sects;
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 4559a1a01b0a..e5b3d99cbe50 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -100,6 +100,9 @@ struct kexec_segment {
> size_t bufsz;
> unsigned long mem;
> size_t memsz;
> +
> + /* Whether this segment is ignored in the checksum calculation. */
> + bool skip_checksum;
> };
>
> #ifdef CONFIG_COMPAT
> @@ -151,15 +154,16 @@ struct kexec_file_ops {
>
> /**
> * struct kexec_buf - parameters for finding a place for a buffer in memory
> - * @image: kexec image in which memory to search.
> - * @buffer: Contents which will be copied to the allocated memory.
> - * @bufsz: Size of @buffer.
> - * @mem: On return will have address of the buffer in memory.
> - * @memsz: Size for the buffer in memory.
> - * @buf_align: Minimum alignment needed.
> - * @buf_min: The buffer can't be placed below this address.
> - * @buf_max: The buffer can't be placed above this address.
> - * @top_down: Allocate from top of memory.
> + * @image: kexec image in which memory to search.
> + * @buffer: Contents which will be copied to the allocated memory.
> + * @bufsz: Size of @buffer.
> + * @mem: On return will have address of the buffer in memory.
> + * @memsz: Size for the buffer in memory.
> + * @buf_align: Minimum alignment needed.
> + * @buf_min: The buffer can't be placed below this address.
> + * @buf_max: The buffer can't be placed above this address.
> + * @top_down: Allocate from top of memory.
> + * @skip_checksum: Don't verify checksum for this buffer in purgatory.
> */
> struct kexec_buf {
> struct kimage *image;
> @@ -171,6 +175,7 @@ struct kexec_buf {
> unsigned long buf_min;
> unsigned long buf_max;
> bool top_down;
> + bool skip_checksum;
> };
>
> int __weak arch_kexec_walk_mem(struct kexec_buf *kbuf,
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index c8418d62e2fc..f6e9958bf578 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -658,6 +658,7 @@ int kexec_add_buffer(struct kexec_buf *kbuf)
> ksegment->bufsz = kbuf->bufsz;
> ksegment->mem = kbuf->mem;
> ksegment->memsz = kbuf->memsz;
> + ksegment->skip_checksum = kbuf->skip_checksum;
> kbuf->image->nr_segments++;
> return 0;
> }
> @@ -672,7 +673,6 @@ static int kexec_calculate_store_digests(struct kimage *image)
> char *digest;
> void *zero_buf;
> struct kexec_sha_region *sha_regions;
> - struct purgatory_info *pi = &image->purgatory_info;
>
> zero_buf = __va(page_to_pfn(ZERO_PAGE(0)) << PAGE_SHIFT);
> zero_buf_sz = PAGE_SIZE;
> @@ -712,11 +712,7 @@ static int kexec_calculate_store_digests(struct kimage *image)
> struct kexec_segment *ksegment;
>
> ksegment = &image->segment[i];
> - /*
> - * Skip purgatory as it will be modified once we put digest
> - * info in purgatory.
> - */
> - if (ksegment->kbuf == pi->purgatory_buf)
> + if (ksegment->skip_checksum)
> continue;
>
> ret = crypto_shash_update(desc, ksegment->kbuf,
> @@ -788,7 +784,7 @@ static int __kexec_load_purgatory(struct kimage *image, unsigned long min,
> Elf_Shdr *sechdrs = NULL;
> struct kexec_buf kbuf = { .image = image, .bufsz = 0, .buf_align = 1,
> .buf_min = min, .buf_max = max,
> - .top_down = top_down };
> + .top_down = top_down, .skip_checksum = true };
>
> /*
> * sechdrs_c points to section headers in purgatory and are read
> @@ -893,7 +889,10 @@ static int __kexec_load_purgatory(struct kimage *image, unsigned long min,
> if (kbuf.buf_align < bss_align)
> kbuf.buf_align = bss_align;
>
> - /* Add buffer to segment list */
> + /*
> + * Add buffer to segment list. Don't checksum the segment as
> + * it will be modified once we put digest info in purgatory.
> + */
> ret = kexec_add_buffer(&kbuf);
> if (ret)
> goto out;
> --
> 1.9.1
>
>
>
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