Subject: Re: [PATCH] efi: libstub/arm: account for firmware reserved memory at the base of RAM

From: Chester Lin <[email-masked]>
Date: Tue, 15 Oct 2019 02:26:28 +0000

On Mon, Oct 14, 2019 at 06:33:09PM +0200, Ard Biesheuvel wrote:
> The EFI stubloader for ARM starts out by allocating a 32 MB window
> at the base of RAM, in order to ensure that the decompressor (which
> blindly copies the uncompressed kernel into that window) does not
> overwrite other allocations that are made while running in the context
> of the EFI firmware.
> 
> In some cases, (e.g., U-Boot running on the Raspberry Pi 2), this is
> causing boot failures because this initial allocation conflicts with
> a page of reserved memory at the base of RAM that contains the SMP spin
> tables and other pieces of firmware data and which was put there by
> the bootloader under the assumption that the TEXT_OFFSET window right
> below the kernel is only used partially during early boot, and will be
> left alone once the memory reservations are processed and taken into
> account.
> 
> So let's permit reserved memory regions to exist in the region starting
> at the base of RAM, and ending at TEXT_OFFSET - 5 * PAGE_SIZE, which is
> the window below the kernel that is not touched by the early boot code.
> 
> Cc: Guillaume Gardet <[email-masked]>
> Cc: Chester Lin <[email-masked]> 
> Signed-off-by: Ard Biesheuvel <[email-masked]>
> ---
>  drivers/firmware/efi/libstub/Makefile     |  1 +
>  drivers/firmware/efi/libstub/arm32-stub.c | 16 +++++++++++++---
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 0460c7581220..ee0661ddb25b 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -52,6 +52,7 @@ lib-$(CONFIG_EFI_ARMSTUB)	+= arm-stub.o fdt.o string.o random.o \
>  
>  lib-$(CONFIG_ARM)		+= arm32-stub.o
>  lib-$(CONFIG_ARM64)		+= arm64-stub.o
> +CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
>  CFLAGS_arm64-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
>  
>  #
> diff --git a/drivers/firmware/efi/libstub/arm32-stub.c b/drivers/firmware/efi/libstub/arm32-stub.c
> index e8f7aefb6813..47aafeff3e01 100644
> --- a/drivers/firmware/efi/libstub/arm32-stub.c
> +++ b/drivers/firmware/efi/libstub/arm32-stub.c
> @@ -195,6 +195,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
>  				 unsigned long dram_base,
>  				 efi_loaded_image_t *image)
>  {
> +	unsigned long kernel_base;
>  	efi_status_t status;
>  
>  	/*
> @@ -204,9 +205,18 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
>  	 * loaded. These assumptions are made by the decompressor,
>  	 * before any memory map is available.
>  	 */
> -	dram_base = round_up(dram_base, SZ_128M);
> +	kernel_base = round_up(dram_base, SZ_128M);
>  
> -	status = reserve_kernel_base(sys_table, dram_base, reserve_addr,
> +	/*
> +	 * Note that some platforms (notably, the Raspberry Pi 2) put
> +	 * spin-tables and other pieces of firmware at the base of RAM,
> +	 * abusing the fact that the window of TEXT_OFFSET bytes at the
> +	 * base of the kernel image is only partially used at the moment.
> +	 * (Up to 5 pages are used for the swapper page table)
> +	 */
> +	kernel_base += TEXT_OFFSET - 5 * PAGE_SIZE;
> +
> +	status = reserve_kernel_base(sys_table, kernel_base, reserve_addr,
>  				     reserve_size);
>  	if (status != EFI_SUCCESS) {
>  		pr_efi_err(sys_table, "Unable to allocate memory for uncompressed kernel.\n");
> @@ -220,7 +230,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
>  	*image_size = image->image_size;
>  	status = efi_relocate_kernel(sys_table, image_addr, *image_size,
>  				     *image_size,
> -				     dram_base + MAX_UNCOMP_KERNEL_SIZE, 0);
> +				     kernel_base + MAX_UNCOMP_KERNEL_SIZE, 0);
>  	if (status != EFI_SUCCESS) {
>  		pr_efi_err(sys_table, "Failed to relocate kernel.\n");
>  		efi_free(sys_table, *reserve_size, *reserve_addr);

Acked-by: Chester Lin <[email-masked]>

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