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Re: [PATCH 2/6] x86/boot: Move compressed kernel to end of decompression buffer

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  Re: [PATCH 2/6] x86/boot: Move compressed kernel to end of  decompression buffer Matt Mullins <mmullins@mmlx.us> - 2016-08-16 06:20 +0200
    Re: [PATCH 2/6] x86/boot: Move compressed kernel to end of  decompression buffer Yinghai Lu <yinghai@kernel.org> - 2016-08-16 21:20 +0200
      Re: [PATCH 2/6] x86/boot: Move compressed kernel to end of  decompression buffer Matt Mullins <mmullins@mmlx.us> - 2016-08-17 04:30 +0200

#1463392 — Re: [PATCH 2/6] x86/boot: Move compressed kernel to end of decompression buffer

[added Simon Glass to CC in case there's some input from u-boot]

On Thu, Apr 28, 2016 at 05:09:04PM -0700, Kees Cook wrote:
> From: Yinghai Lu <yinghai@kernel.org>
> 
> This patch adds BP_init_size (which is the INIT_SIZE as passed in from
> the boot_params) into asm-offsets.c to make it visible to the assembly
> code. Then when moving the ZO, it calculates the starting position of
> the copied ZO (via BP_init_size and the ZO run size) so that the VO__end
> will be at the end of the decompression buffer. To make the position
> calculation safe, the end of ZO is page aligned (and a comment is added
> to the existing VO alignment for good measure).

> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index d43c30ed89ed..09cdc0c3ee7e 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -338,7 +340,9 @@ preferred_addr:
>  1:
>  
>  	/* Target address to relocate to for decompression */
> -	leaq	z_extract_offset(%rbp), %rbx
> +	movl	BP_init_size(%rsi), %ebx
> +	subl	$_end, %ebx
> +	addq	%rbp, %rbx
>  
>  	/* Set up the stack */
>  	leaq	boot_stack_end(%rbx), %rsp

This appears to have a negative effect on booting the Intel Edison platform, as
it uses u-boot as its bootloader.  u-boot does not copy the init_size parameter
when booting a bzImage: it copies a fixed-size setup_header [1], and its
definition of setup_header doesn't include the parameters beyond setup_data [2].

With a zero value for init_size, this calculates a %rsp value of 0x101ff9600.
This causes the boot process to hard-stop at the immediately-following pushq, as
this platform has no usable physical addresses above 4G.

What are the options for getting this type of platform to function again?  For
now, kexec from a working Linux system does seem to be a work-around, but there
appears to be other x86 hardware using u-boot: the chromium.org folks seem to be
maintaining the u-boot x86 tree.

[1] http://git.denx.de/?p=u-boot.git;a=blob;f=arch/x86/lib/zimage.c;h=1b33c771391f49ffe82864ff1582bdfd07e5e97d;hb=HEAD#l156
[2] http://git.denx.de/?p=u-boot.git;a=blob;f=arch/x86/include/asm/bootparam.h;h=140095117e5a2daef0a097c55f0ed10e08acc781;hb=HEAD#l24

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#1464018

On Mon, Aug 15, 2016 at 9:01 PM, Matt Mullins <mmullins@mmlx.us> wrote:
>
> This appears to have a negative effect on booting the Intel Edison platform, as
> it uses u-boot as its bootloader.  u-boot does not copy the init_size parameter
> when booting a bzImage: it copies a fixed-size setup_header [1], and its
> definition of setup_header doesn't include the parameters beyond setup_data [2].
>
> With a zero value for init_size, this calculates a %rsp value of 0x101ff9600.
> This causes the boot process to hard-stop at the immediately-following pushq, as
> this platform has no usable physical addresses above 4G.
>
> What are the options for getting this type of platform to function again?  For
> now, kexec from a working Linux system does seem to be a work-around, but there
> appears to be other x86 hardware using u-boot: the chromium.org folks seem to be
> maintaining the u-boot x86 tree.
>
> [1] http://git.denx.de/?p=u-boot.git;a=blob;f=arch/x86/lib/zimage.c;h=1b33c771391f49ffe82864ff1582bdfd07e5e97d;hb=HEAD#l156
> [2] http://git.denx.de/?p=u-boot.git;a=blob;f=arch/x86/include/asm/bootparam.h;h=140095117e5a2daef0a097c55f0ed10e08acc781;hb=HEAD#l24

Then should fix the u-boot about header_size assumption.
correct way should be like kexec one:

        /* only copy setup_header */
        setup_header_size = kernel[0x201] + 0x202 - 0x1f1;
        if (setup_header_size > 0x7f)
                setup_header_size = 0x7f;
        memcpy((unsigned char *)real_mode + 0x1f1, kernel + 0x1f1,
                 setup_header_size);

need get setup_header_size at first before copying.

setup_base->hdr = params->hdr;

===>
        unsigned long setup_header_size;

        setup_header_size = image[0x201] + 0x202 - 0x1f1;
        if (setup_header_size > 0x7f)
                setup_header_size = 0x7f;

        memcpy((unsigned char *)&setup_base->hdr, &params->hdr,
                 setup_header_size);

Thanks

Yinghai

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#1464289

On Tue, Aug 16, 2016 at 12:19:42PM -0700, Yinghai Lu wrote:
> On Mon, Aug 15, 2016 at 9:01 PM, Matt Mullins <mmullins@mmlx.us> wrote:
> >
> > This appears to have a negative effect on booting the Intel Edison platform, as
> > it uses u-boot as its bootloader.  u-boot does not copy the init_size parameter
> > when booting a bzImage: it copies a fixed-size setup_header [1], and its
> > definition of setup_header doesn't include the parameters beyond setup_data [2].
> >
> > With a zero value for init_size, this calculates a %rsp value of 0x101ff9600.
> > This causes the boot process to hard-stop at the immediately-following pushq, as
> > this platform has no usable physical addresses above 4G.
> >
> > What are the options for getting this type of platform to function again?  For
> > now, kexec from a working Linux system does seem to be a work-around, but there
> > appears to be other x86 hardware using u-boot: the chromium.org folks seem to be
> > maintaining the u-boot x86 tree.
> >
> > [1] http://git.denx.de/?p=u-boot.git;a=blob;f=arch/x86/lib/zimage.c;h=1b33c771391f49ffe82864ff1582bdfd07e5e97d;hb=HEAD#l156
> > [2] http://git.denx.de/?p=u-boot.git;a=blob;f=arch/x86/include/asm/bootparam.h;h=140095117e5a2daef0a097c55f0ed10e08acc781;hb=HEAD#l24
> 
> Then should fix the u-boot about header_size assumption.

I was hoping to avoid that, since the Edison's u-boot is 10,000-line patch atop
the upstream -- I don't trust myself to build and flash one quite yet.

If this turned out to affect Chromebooks, I'd spend more effort pushing for
a kernel fix, but it seems that ChromeOS has a different kernel load procedure
and doesn't use "zboot".  For now, I'll probably just keep a local patch that
hard-codes a value large enough to decompress and launch the kernel.

I may turn that local patch into something gated by a Kconfig eventually, in
hopes that users of the other x86 u-boot platforms will see it in a "make
oldconfig" run.

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