Re: Using memdisk with grub2 and a gzip-compressed ISO

[Vladimir 'phcoder' Serbinenko]

On Apr 29, 2015 7:45 PM, "Andrei Borzenkov" <address@hidden> wrote:
>
> В Thu, 23 Apr 2015 10:23:09 -0400
> David Shaw <address@hidden> пишет:
>
> >
> > When booting the box with grub2 2.02, it does not work.  The error is:
> >
> >   Ramdisk at 0x37979000, length 0x0033b290
> >   gzip image: decompressed addr 0xbfff7000, len 0x00008f58: failed
> >   Decompression error: output buffer overrun
> >
>
> Could you test attached patch? While I'm past this message using your
> archive, in qemu-kvm it hangs after "... booting ..." and in
> qemu-system-i386 I get something that looks like memory corruption with
> occasional crash when initrd is uncompressed.
>
> From: Andrei Borzenkov <address@hidden>
> Subject: [PATCH] loader/linux: do not pad initrd with zeroes at the end
>
> Syslinux memdisk is using initrd image and needs to know uncompressed
> size in advance. For gzip uncompressed size is at the end of compressed
> stream. Grub padded each input file to 4 bytes at the end, which means
> syslinux got wrong size.
>
> Linux initramfs loader apparently does not care about trailing alignment.
> So change code to align beginning of each file instead which
> automatically gives us the correct size for single file.
>
> Reported-By: David Shaw <address@hidden>
>
> ---
>  grub-core/loader/linux.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/grub-core/loader/linux.c b/grub-core/loader/linux.c
> index 117232f..35b858e 100644
> --- a/grub-core/loader/linux.c
> +++ b/grub-core/loader/linux.c
> @@ -161,6 +161,9 @@ grub_initrd_init (int argc, char *argv[],
>    for (i = 0; i < argc; i++)
>      {
>        const char *fname = argv[i];
> +
> +      initrd_ctx->size = ALIGN_UP (initrd_ctx->size, 4);
> +
>        if (grub_memcmp (argv[i], "newc:", 5) == 0)
>         {
>           const char *ptr, *eptr;
> @@ -205,7 +208,7 @@ grub_initrd_init (int argc, char *argv[],
>        initrd_ctx->nfiles++;
>        initrd_ctx->components[i].size
>         = grub_file_size (initrd_ctx->components[i].file);
> -      initrd_ctx->size += ALIGN_UP (initrd_ctx->components[i].size, 4);
> +      initrd_ctx->size += initrd_ctx->components[i].size;
>      }
>
>    if (newc)
> @@ -253,6 +256,9 @@ grub_initrd_load (struct grub_linux_initrd_context *initrd_ctx,
>      {
>        grub_ssize_t cursize;
>
> +      grub_memset (ptr, 0, ALIGN_UP_OVERHEAD ((grub_addr_t)ptr, 4));
> +      ptr += ALIGN_UP_OVERHEAD ((grub_addr_t)ptr, 4);
> +
Please don't abuse the pointer this way.
Also thinking about it, I think that the allocation for initrd should be page-aligned and have integer number of pages if it's not the case already. I'll check when I get home
>        if (initrd_ctx->components[i].newc_name)
>         {
>           ptr += insert_dir (initrd_ctx->components[i].newc_name,
> @@ -283,8 +289,6 @@ grub_initrd_load (struct grub_linux_initrd_context *initrd_ctx,
>           return grub_errno;
>         }
>        ptr += cursize;
> -      grub_memset (ptr, 0, ALIGN_UP_OVERHEAD (cursize, 4));
> -      ptr += ALIGN_UP_OVERHEAD (cursize, 4);
>      }
>    if (newc)
>      ptr = make_header (ptr, "TRAILER!!!", sizeof ("TRAILER!!!") - 1, 0, 0);
> --
> tg: (104dff3..) u/initrd-pad (depends on: master)
>
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