[U-Boot] [PATCH 04/11] spl: imx: Add optional lds to keep SPL entirely in on-chip RAM

[Stefano Babic]

Hi Henry,

On 14/07/2018 02:11, Henry Beberman wrote:
> From: Henry Beberman <henry.beberman at microsoft.com>
> 
> This patch is part of the i.MX Windows 10 IoT Core boot flow.
> 
> It adds a modified linker script for SPL to keep all segments in
> on-chip ram. This is to harden the device against potential leaks of
> device secrets by keeping them out of DRAM.
> 
> Additionally if CONFIG_SYS_SPL_MALLOC_START is defined, it will
> override the CONFIG_SPL_SYS_MALLOC_SIMPLE and allocate space in DRAM
> instead of on-chip ram. This patch prevents the definition of those
> values for i.MX6 and i.MX7 SPL if CONFIG_OPTEE_SPL_BOOT is selected.
> 

I guess there should be some kind of restrictions to be set according to
the i.MX6 variant. I have already had some projects where I get rid of
all space available on OCRAM. The smaller i.MX6 has just 64KB of RAM -
have you tested also on them ? I wonder if there is enough space for all
i.MX variants, specially if some other options are enabled.

> Signed-off-by: Henry Beberman <henry.beberman at microsoft.com>
> Cc: Stefano Babic <sbabic at denx.de>
> Cc: Fabio Estevam <fabio.estevam at nxp.com>
> ---
>  arch/arm/mach-imx/u-boot-spl-sram.lds | 59 +++++++++++++++++++++++++++++++++++
>  include/configs/imx6_spl.h            |  2 ++
>  include/configs/imx7_spl.h            |  2 ++
>  3 files changed, 63 insertions(+)
>  create mode 100644 arch/arm/mach-imx/u-boot-spl-sram.lds
> 
> diff --git a/arch/arm/mach-imx/u-boot-spl-sram.lds b/arch/arm/mach-imx/u-boot-spl-sram.lds
> new file mode 100644
> index 0000000000..dfbb4aef5d
> --- /dev/null
> +++ b/arch/arm/mach-imx/u-boot-spl-sram.lds
> @@ -0,0 +1,59 @@
> +/*
> + * (C) Copyright 2002
> + * Gary Jennejohn, DENX Software Engineering, <garyj at denx.de>
> + *
> + * (C) Copyright 2010
> + * Texas Instruments, <www.ti.com>
> + *	Aneesh V <aneesh at ti.com>
> + *
> + * (C) Copyright 2018 Microsoft Corporation
> + *
> + * SPDX-License-Identifier:	GPL-2.0+
> + */
> +
> +MEMORY { .sram : ORIGIN = CONFIG_SPL_TEXT_BASE,\
> +		LENGTH = CONFIG_SPL_MAX_SIZE }
> +
> +OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
> +OUTPUT_ARCH(arm)
> +ENTRY(_start)
> +SECTIONS
> +{
> +	.text      :
> +	{
> +		__start = .;
> +		*(.vectors)
> +		arch/arm/cpu/armv7/start.o	(.text*)
> +		*(.text*)
> +	} >.sram
> +
> +	. = ALIGN(4);
> +	.rodata : { *(SORT_BY_ALIGNMENT(.rodata*)) } >.sram
> +
> +	. = ALIGN(4);
> +	.data : { *(SORT_BY_ALIGNMENT(.data*)) } >.sram
> +
> +	. = ALIGN(4);
> +	.u_boot_list : {
> +		KEEP(*(SORT(.u_boot_list*)));
> +	} >.sram
> +
> +	. = ALIGN(4);
> +	__image_copy_end = .;
> +
> +	.end :
> +	{
> +		*(.__end)
> +	}
> +
> +	_image_binary_end = .;
> +
> +	.bss :
> +	{
> +		. = ALIGN(4);
> +		__bss_start = .;
> +		*(.bss*)
> +		. = ALIGN(4);
> +		__bss_end = .;
> +	} >.sram
> +}

This is more or less a copy of the armv8 version + bss in sram instead
of sdram. In any case, mach-imx is not the right place because it is
quite SOC independent. The whole i.MX do not use own lds but they are
using the general scripts from ARM 32bit.

> diff --git a/include/configs/imx6_spl.h b/include/configs/imx6_spl.h
> index 720ff045a7..4088e8a936 100644
> --- a/include/configs/imx6_spl.h
> +++ b/include/configs/imx6_spl.h
> @@ -51,6 +51,7 @@
>  # endif
>  #endif
>  
> +#ifndef CONFIG_OPTEE_SPL_BOOT
>  #if defined(CONFIG_MX6SX) || defined(CONFIG_MX6SL) || \
>  	defined(CONFIG_MX6UL) || defined(CONFIG_MX6ULL)
>  #define CONFIG_SPL_BSS_START_ADDR      0x88200000
> @@ -63,6 +64,7 @@
>  #define CONFIG_SYS_SPL_MALLOC_START	0x18300000
>  #define CONFIG_SYS_SPL_MALLOC_SIZE	0x100000	/* 1 MB */
>  #endif
> +#endif /* !CONFIG_OPTEE_SPL_BOOT */
>  #endif
>  
>  #endif
> diff --git a/include/configs/imx7_spl.h b/include/configs/imx7_spl.h
> index 1eb6cd894d..5dd4aed652 100644
> --- a/include/configs/imx7_spl.h
> +++ b/include/configs/imx7_spl.h
> @@ -46,10 +46,12 @@
>  # endif
>  #endif
>  
> +#ifndef CONFIG_OPTEE_SPL_BOOT
>  #define CONFIG_SPL_BSS_START_ADDR      0x88200000
>  #define CONFIG_SPL_BSS_MAX_SIZE        0x100000		/* 1 MB */
>  #define CONFIG_SYS_SPL_MALLOC_START    0x88300000
>  #define CONFIG_SYS_SPL_MALLOC_SIZE     0x100000		/* 1 MB */
> +#endif /* !CONFIG_OPTEE_SPL_BOOT */
>  
>  #endif /* CONFIG_SPL */

Best regards,
Stefano Babic

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