linux-kernel - Re: [PATCH] efi/x86: Only copy the compressed kernel image in efi_relocate

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Message-ID: <CAMj1kXGBybyTOADr+PvC+ZVohw+aRZbEnfweHTECKKdX9JHXTw@mail.gmail.com>
Date:   Sun, 25 Oct 2020 17:28:06 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] efi/x86: Only copy the compressed kernel image in efi_relocate_kernel()

On Sun, 25 Oct 2020 at 17:19, Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Sun, Oct 11, 2020 at 10:20:12AM -0400, Arvind Sankar wrote:
> > 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@...m.mit.edu>
>
> Ping
>

I'll pick this up as a fix once the merge window closes.

> > ---
> >  drivers/firmware/efi/libstub/x86-stub.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> > index 3672539cb96e..f14c4ff5839f 100644
> > --- a/drivers/firmware/efi/libstub/x86-stub.c
> > +++ b/drivers/firmware/efi/libstub/x86-stub.c
> > @@ -715,8 +715,11 @@ unsigned long efi_main(efi_handle_t handle,
> >           (IS_ENABLED(CONFIG_X86_32) && buffer_end > KERNEL_IMAGE_SIZE)    ||
> >           (IS_ENABLED(CONFIG_X86_64) && buffer_end > MAXMEM_X86_64_4LEVEL) ||
> >           (image_offset == 0)) {
> > +             extern char _bss[];
> > +
> >               status = efi_relocate_kernel(&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);
> > --
> > 2.26.2
> >