From: Ard Biesheuvel <ardb@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Michael Roth <michael.roth@amd.com>
Subject: Re: [PATCH v2 04/16] x86/compressed: efi-mixed: move efi32_pe_entry into .text section
Date: Thu, 17 Nov 2022 17:06:37 +0100 [thread overview]
Message-ID: <CAMj1kXEf=fCwGLakttfAkyGYj4PFrahcAj0GiMCUFVnOyaZtRw@mail.gmail.com> (raw)
In-Reply-To: <Y3ZZ35vJBh4fQu9M@zn.tnic>
On Thu, 17 Nov 2022 at 16:57, Borislav Petkov <bp@alien8.de> wrote:
>
> On Wed, Sep 21, 2022 at 04:54:10PM +0200, Ard Biesheuvel wrote:
> > /*
> > * We need to set the image_offset variable here since startup_32() will
> > * use it before we get to the 64-bit efi_pe_entry() in C code.
> > */
> > - subl %esi, %ebx
> > - movl %ebx, rva(image_offset)(%ebp) // save image_offset
> > + subl %esi, %ebp // calculate image_offset
> > + movl %ebp, (image_offset - 1b)(%ebx) // save image_offset
>
> All looks ok, just one question: what was the reason for that
> image_offset thing?
>
> I see:
>
> 1887c9b653f9 ("efi/x86: Decompress at start of PE image load address")
>
> It says that if the kernel is loaded as a PE executable using
> LoadImage() we don't know where that image will be loaded each time so
> we're saving that offset for later when relocating (or not) the kernel?
>
> All part of those improvements:
>
> https://lore.kernel.org/all/20200301230537.2247550-1-nivedita@alum.mit.edu/
>
> Am I close?
>
Yes.
The x86 boot protocol does not require that the setup data block comes
right before the image, it just receives the address in %esi
When doing PE boot, this is guaranteed, and so we can reuse the memory
before the image.
> I.e., that image_offset is purely a kernel thing and not something EFI
> LoadImage's inner workings mandate...? It doesn't seem so from where I'm
> standing but lemme doublecheck still.
>
No this has nothing do with the EFI in particular, only with how the
x86 boot image is constructed and wrapped into a PE/COFF executable.
next prev parent reply other threads:[~2022-11-17 16:07 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-21 14:54 [PATCH v2 00/16] x86: head_64.S spring cleaning Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 01/16] x86/compressed: efi-mixed: rename efi_thunk_64.S to efi-mixed.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 02/16] x86/compressed: efi-mixed: move 32-bit entrypoint code into .text section Ard Biesheuvel
2022-10-06 10:42 ` Borislav Petkov
2022-10-06 10:56 ` Ard Biesheuvel
2022-10-06 11:13 ` Borislav Petkov
2022-10-06 11:19 ` Ard Biesheuvel
2022-10-06 12:27 ` Ard Biesheuvel
2022-10-07 8:56 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 03/16] x86/compressed: efi-mixed: move bootargs parsing out of 32-bit startup code Ard Biesheuvel
2022-10-06 11:03 ` Borislav Petkov
2022-10-06 11:29 ` Ard Biesheuvel
2022-10-07 9:30 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 04/16] x86/compressed: efi-mixed: move efi32_pe_entry into .text section Ard Biesheuvel
2022-11-17 15:57 ` Borislav Petkov
2022-11-17 16:06 ` Ard Biesheuvel [this message]
2022-11-17 17:08 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 05/16] x86/compressed: efi-mixed: move efi32_entry out of head_64.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 06/16] x86/compressed: efi-mixed: move efi32_pe_entry() " Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 07/16] x86/compressed: efi: merge multiple definitions of image_offset into one Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 08/16] x86/compressed: efi-mixed: simplify IDT/GDT preserve/restore Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 09/16] x86/compressed: avoid touching ECX in startup32_set_idt_entry() Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 10/16] x86/compressed: pull global variable ref up into startup32_load_idt() Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 11/16] x86/compressed: move startup32_load_idt() into .text section Ard Biesheuvel
2022-11-18 16:44 ` Borislav Petkov
2022-09-21 14:54 ` [PATCH v2 12/16] x86/compressed: move startup32_load_idt() out of head_64.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 13/16] x86/compressed: move startup32_check_sev_cbit() into .text Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 14/16] x86/compressed: move startup32_check_sev_cbit() out of head_64.S Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 15/16] x86/compressed: adhere to calling convention in get_sev_encryption_bit() Ard Biesheuvel
2022-09-21 14:54 ` [PATCH v2 16/16] x86/compressed: only build mem_encrypt.S if AMD_MEM_ENCRYPT=y Ard Biesheuvel
2022-11-18 18:26 ` [PATCH v2 00/16] x86: head_64.S spring cleaning Borislav Petkov
2022-11-18 23:31 ` Ard Biesheuvel
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