Re: [PATCH 2/5] efi/x86: Decompress at start of PE image load address

From: "Mika Penttilä" <mika.penttila@nextfour.com>
To: Arvind Sankar <nivedita@alum.mit.edu>, Ard Biesheuvel <ardb@kernel.org>
Cc: "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/5] efi/x86: Decompress at start of PE image load address
Date: Tue, 3 Mar 2020 06:28:20 +0000	[thread overview]
Message-ID: <dce7e026-ccb2-36f0-c892-83558dcc055f@nextfour.com> (raw)
In-Reply-To: <20200301230537.2247550-3-nivedita@alum.mit.edu>

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On 2.3.2020 1.05, Arvind Sankar wrote:
> When booted via PE loader, define image_offset to hold the offset of
> startup_32 from the start of the PE image, and use it as the start of
> the decompression buffer.
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> ---
>  arch/x86/boot/compressed/head_32.S      | 17 +++++++++++
>  arch/x86/boot/compressed/head_64.S      | 38 +++++++++++++++++++++++--
>  drivers/firmware/efi/libstub/x86-stub.c | 12 ++++++--
>  3 files changed, 61 insertions(+), 6 deletions(-)

...
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -19,6 +19,7 @@
>  
>  static efi_system_table_t *sys_table;
>  extern const bool efi_is64;
> +extern u32 image_offset;
>  
>  __pure efi_system_table_t *efi_system_table(void)
>  {
> @@ -364,6 +365,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
>  	struct boot_params *boot_params;
>  	struct setup_header *hdr;
>  	efi_loaded_image_t *image;
> +	void *image_base;
>  	efi_guid_t proto = LOADED_IMAGE_PROTOCOL_GUID;
>  	int options_size = 0;
>  	efi_status_t status;
> @@ -384,7 +386,10 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
>  		efi_exit(handle, status);
>  	}
>  
> -	hdr = &((struct boot_params *)efi_table_attr(image, image_base))->hdr;
> +	image_base = efi_table_attr(image, image_base);
> +	image_offset = (void *)startup_32 - image_base;

startup_32 == 0, so maybe something like

leaq	startup_32(%rip) - image_base

should be used ?

> +
> +	hdr = &((struct boot_params *)image_base)->hdr;
>  	above4g = hdr->xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G;
>  
>  	status = efi_allocate_pages(0x4000, (unsigned long *)&boot_params,
> @@ -399,7 +404,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
>  	hdr = &boot_params->hdr;
>  
>  	/* Copy the second sector to boot_params */
> -	memcpy(&hdr->jump, efi_table_attr(image, image_base) + 512, 512);
> +	memcpy(&hdr->jump, image_base + 512, 512);
>  
>  	/*
>  	 * Fill out some of the header fields ourselves because the
> @@ -726,7 +731,7 @@ unsigned long efi_main(efi_handle_t handle,
>  	 * If the kernel isn't already loaded at the preferred load
>  	 * address, relocate it.
>  	 */
> -	if (bzimage_addr != hdr->pref_address) {
> +	if (bzimage_addr - image_offset != hdr->pref_address) {
>  		status = efi_relocate_kernel(&bzimage_addr,
>  					     hdr->init_size, hdr->init_size,
>  					     hdr->pref_address,
> @@ -736,6 +741,7 @@ unsigned long efi_main(efi_handle_t handle,
>  			efi_printk("efi_relocate_kernel() failed!\n");
>  			goto fail;
>  		}
> +		image_offset = 0;
>  	}
>  
>  	/*

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