diff mbox series

[focal:linux-azure-cvm,1/1] efi/x86: Only copy the compressed kernel image in efi_relocate_kernel()

Message ID 20220627233837.1263654-2-marcelo.cerri@canonical.com
State New
Headers show
Series LP:#1980023 - Properly realocate the the kernel image | expand

Commit Message

Marcelo Henrique Cerri June 27, 2022, 11:38 p.m. UTC 
From: Arvind Sankar <nivedita@alum.mit.edu>

BugLink: https://bugs.launchpad.net/bugs/1980023

The image_size argument to efi_relocate_kernel() is currently specified
as init_size, but this is unnecessarily large. The compressed kernel is
much smaller, in fact, its image only extends up to the start of _bss,
since at this point, the .bss section is still uninitialized.

Depending on compression level, this can reduce the amount of data
copied by 4-5x.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20201011142012.96493-1-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
(back ported from commit 688eb28211abdf82a3f51e8997f1c8137947227d)
[marcelo.cerri: replicate the same change in eboot.c instead because
 it was merged into libstub in 5.7 by c2d0b470154c]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
---
 arch/x86/boot/compressed/eboot.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Luke Nowakowski-Krijger June 28, 2022, 1:30 a.m. UTC | #1 
Acked-by: Luke Nowakowski-Krijger <luke.nowakowskikrijger@canonical.com>

On Mon, Jun 27, 2022 at 4:39 PM Marcelo Henrique Cerri <
marcelo.cerri@canonical.com> wrote:

> From: Arvind Sankar <nivedita@alum.mit.edu>
>
> BugLink: https://bugs.launchpad.net/bugs/1980023
>
> The image_size argument to efi_relocate_kernel() is currently specified
> as init_size, but this is unnecessarily large. The compressed kernel is
> much smaller, in fact, its image only extends up to the start of _bss,
> since at this point, the .bss section is still uninitialized.
>
> Depending on compression level, this can reduce the amount of data
> copied by 4-5x.
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> Link:
> https://lore.kernel.org/r/20201011142012.96493-1-nivedita@alum.mit.edu
> Signed-off-by
> <https://lore.kernel.org/r/20201011142012.96493-1-nivedita@alum.mit.eduSigned-off-by>:
> Ard Biesheuvel <ardb@kernel.org>
> (back ported from commit 688eb28211abdf82a3f51e8997f1c8137947227d)
> [marcelo.cerri: replicate the same change in eboot.c instead because
>  it was merged into libstub in 5.7 by c2d0b470154c]
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
> ---
>  arch/x86/boot/compressed/eboot.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/boot/compressed/eboot.c
> b/arch/x86/boot/compressed/eboot.c
> index 82bc60c8acb2..59a5ea4f64f9 100644
> --- a/arch/x86/boot/compressed/eboot.c
> +++ b/arch/x86/boot/compressed/eboot.c
> @@ -810,9 +810,11 @@ efi_main(struct efi_config *c, struct boot_params
> *boot_params)
>          * address, relocate it.
>          */
>         if (hdr->pref_address != hdr->code32_start) {
> +               extern char _bss[];
>                 unsigned long bzimage_addr = hdr->code32_start;
>                 status = efi_relocate_kernel(sys_table, &bzimage_addr,
> -                                            hdr->init_size,
> hdr->init_size,
> +                                            (unsigned long)_bss -
> bzimage_addr,
> +                                            hdr->init_size,
>                                              hdr->pref_address,
>                                              hdr->kernel_alignment,
>                                              LOAD_PHYSICAL_ADDR);
> --
> 2.25.1
>
>
> --
> kernel-team mailing list
> kernel-team@lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
>
diff mbox series

Patch

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index 82bc60c8acb2..59a5ea4f64f9 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -810,9 +810,11 @@  efi_main(struct efi_config *c, struct boot_params *boot_params)
 	 * address, relocate it.
 	 */
 	if (hdr->pref_address != hdr->code32_start) {
+		extern char _bss[];
 		unsigned long bzimage_addr = hdr->code32_start;
 		status = efi_relocate_kernel(sys_table, &bzimage_addr,
-					     hdr->init_size, hdr->init_size,
+					     (unsigned long)_bss - bzimage_addr,
+					     hdr->init_size,
 					     hdr->pref_address,
 					     hdr->kernel_alignment,
 					     LOAD_PHYSICAL_ADDR);