[PATCH] Load bzImages smaller than 32 KiB

[Simon Horman]

On Fri, Jun 01, 2012 at 10:59:32AM -0500, Eric Biggers wrote:
> Allow bzImages smaller than 32KiB to be kexec'ed.
> 
> The current code will fail to load a bzImage smaller than 32768 bytes (sizeof
> struct x86_linux_header), but the 'memdisk' program that comes with syslinux is
> only about 26 KiB.  This patch changes the minimum size to 1024 bytes (2
> sectors), which appears to be the limit that syslinux enforces.
> 
> Removed the "tail" field of struct x86_linux_header because it doesn't seem to
> actually be used (is there a reason for it?).
> 
> Also, note that bzImage_probe() was incorrectly using `sizeof (header)', even
> though header is a pointer.

Hi Eric,

could you please supply a signed-off-by line so I can apply this patch?

Thanks.

> 
> diff --git a/include/x86/x86-linux.h b/include/x86/x86-linux.h
> index 59d35c9..2ebcc3a 100644
> --- a/include/x86/x86-linux.h
> +++ b/include/x86/x86-linux.h
> @@ -233,7 +233,6 @@ struct x86_linux_header {
>  	uint32_t high_base;			/* 0x24C */
>  	uint32_t high_memsz;			/* 0x250 */
>  	uint32_t high_filesz;			/* 0x254 */
> -	uint32_t tail[32*1024 - 0x258];		/* 0x258 */
>  #else
>  	uint32_t kernel_alignment;		/* 0x230 */
>  	uint8_t  relocatable_kernel;		/* 0x234 */
> @@ -241,7 +240,6 @@ struct x86_linux_header {
>  	uint32_t cmdline_size;                  /* 0x238 */
>  	uint32_t hardware_subarch;              /* 0x23C */
>  	uint64_t hardware_subarch_data;         /* 0x240 */
> -	uint8_t  tail[32*1024 - 0x248];		/* 0x248 */
>  #endif
>  } PACKED;
>  
> diff --git a/kexec/arch/i386/kexec-bzImage.c b/kexec/arch/i386/kexec-bzImage.c
> index 54c4427..6998587 100644
> --- a/kexec/arch/i386/kexec-bzImage.c
> +++ b/kexec/arch/i386/kexec-bzImage.c
> @@ -44,7 +44,10 @@ static const int probe_debug = 0;
>  int bzImage_probe(const char *buf, off_t len)
>  {
>  	const struct x86_linux_header *header;
> -	if ((uintmax_t)len < (uintmax_t)sizeof(header)) {
> +	if ((uintmax_t)len < (uintmax_t)(2 * 512)) {
> +		if (probe_debug) {
> +			fprintf(stderr, "File is too short to be a bzImage!\n");
> +		}
>  		return -1;
>  	}
>  	header = (const struct x86_linux_header *)buf;
> @@ -118,7 +121,7 @@ int do_bzImage_load(struct kexec_info *info,
>  	/*
>  	 * Find out about the file I am about to load.
>  	 */
> -	if ((uintmax_t)kernel_len < (uintmax_t)sizeof(setup_header)) {
> +	if ((uintmax_t)kernel_len < (uintmax_t)(2 * 512)) {
>  		return -1;
>  	}
>  	memcpy(&setup_header, kernel, sizeof(setup_header));
> 
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>