From: Ard Biesheuvel <ardb@kernel.org>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: linux-efi <linux-efi@vger.kernel.org>,
Alexander Graf <agraf@csgraf.de>,
Daniel Kiper <daniel.kiper@oracle.com>,
Matthew Garrett <mjg59@google.com>,
Michael Brown <mbrown@fensystems.co.uk>,
Hans de Goede <hdegoede@redhat.com>,
Peter Jones <pjones@redhat.com>,
Leif Lindholm <leif@nuviainc.com>,
Laszlo Ersek <lersek@redhat.com>, Ingo Molnar <mingo@kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 3/3] efi/x86: implement mixed mode boot without the handover protocol
Date: Thu, 13 Feb 2020 17:42:22 +0000 [thread overview]
Message-ID: <CAKv+Gu8KX4wFOx-GObTt2Z7k5v+BG=s35S-sqfrXg93xJ6mFjw@mail.gmail.com> (raw)
In-Reply-To: <20200213172355.GB1400002@rani.riverdale.lan>
On Thu, 13 Feb 2020 at 18:23, Arvind Sankar <nivedita@alum.mit.edu> wrote:
>
> On Thu, Feb 13, 2020 at 03:59:28PM +0100, Ard Biesheuvel wrote:
> > Add support for booting 64-bit x86 kernels from 32-bit firmware running
> > on 64-bit capable CPUs without requiring the bootloader to implement
> > the EFI handover protocol, allocate the setup block etc etc, all of
> > which can be done by the stub using code we have already implemented.
> >
> > Instead, create an ordinary EFI application entrypoint but implemented
> > in 32-bit code, so that it can be invoked by 32-bit firmware, and stash
> > the address of this 32-bit entrypoint in the .compat section where the
> > bootloader can find it.
> >
> > Note that we use the setup block embedded in the binary to go through
> > startup_32(), but it gets reallocated and copied in efi_pe_entry(),
> > using the same code that runs when the x86 kernel is booted in EFI
> > mode from native firmware. This requires the loaded image protocol to
> > be installed on the kernel image's EFI handle, and point to the kernel
> > image itself and not to its loader. This, in turn, requires the
> > bootloader to use the LoadImage() boot services to load the 64-bit
> > image from 32-bit firmware, which is in fact supported by firmware
> > based on EDK2. (Only StartImage() will fail, and instead, the newly
> > added entrypoint needs to be invoked)
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> > arch/x86/boot/compressed/head_64.S | 61 +++++++++++++++++++-
> > 1 file changed, 59 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> > index a4f5561c1c0e..7baaf9c97f5a 100644
> > --- a/arch/x86/boot/compressed/head_64.S
> > +++ b/arch/x86/boot/compressed/head_64.S
> > @@ -207,8 +207,8 @@ SYM_FUNC_START(startup_32)
> > cmp $0, %edi
> > jz 1f
> > leal efi64_stub_entry(%ebp), %eax
> > - movl %esi, %edx
> > movl efi32_boot_args+4(%ebp), %esi
> > + movl efi32_boot_args+8(%ebp), %edx // saved bootparams pointer
> > 1:
> > #endif
> > pushl %eax
> > @@ -233,6 +233,8 @@ SYM_FUNC_START(efi32_stub_entry)
> > 1: pop %ebp
> > subl $1b, %ebp
> >
> > + movl %esi, efi32_boot_args+8(%ebp)
> > +2:
>
> I think it would be easier to read if this were turned into a proper
> SYM_INNER_LABEL. You could then also just put efi32_pe_entry into the
> .text section instead of moving it to the end of .head.text with
> .subsection. Another option is to use a separate flag in .data to
> indicate that we entered via efi32_pe_entry, then you could just jump
> to efi32_stub_entry.
>
Indeed.
> > movl %ecx, efi32_boot_args(%ebp)
> > movl %edx, efi32_boot_args+4(%ebp)
> > movb $0, efi_is64(%ebp)
> > @@ -249,6 +251,49 @@ SYM_FUNC_START(efi32_stub_entry)
> >
> > jmp startup_32
> > SYM_FUNC_END(efi32_stub_entry)
> > +
> > +#define ST32_boottime 60 // offsetof(efi_system_table_32_t, boottime)
> > +#define BS32_handle_protocol 88 // offsetof(efi_boot_services_32_t, handle_protocol)
> > +#define LI32_image_base 32 // offsetof(efi_loaded_image_32_t, image_base)
> > +
> > + .subsection 1
> > + .code32
> > +SYM_FUNC_START(efi32_pe_entry)
> > + pushl %ebp
> > +
> > + call 3f
> > +3: pop %ebp
> > + subl $3b, %ebp
> > +
> > + /* Get the loaded image protocol pointer from the image handle */
> > + subl $12, %esp // space for the loaded image pointer
> > + pushl %esp // pass its address
> > + leal 5f(%ebp), %eax
> > + pushl %eax // pass the GUID address
> > + pushl 28(%esp) // pass the image handle
> > +
> > + movl 36(%esp), %eax // sys_table
> > + movl ST32_boottime(%eax), %eax // sys_table->boottime
> > + call *BS32_handle_protocol(%eax) // sys_table->boottime->handle_protocol
> > + cmp $0, %eax
> > + jnz 4f
> > +
> > + movl 32(%esp), %ecx // image_handle
> > + movl 36(%esp), %edx // sys_table
> > + movl 12(%esp), %esi // loaded_image
> > + movl LI32_image_base(%esi), %esi // loaded_image->image_base
> > + jmp 2b
> > +
> > +4: addl $24, %esp
> > + popl %ebp
> > + ret
> > +SYM_FUNC_END(efi32_pe_entry)
> > +
> > + /* EFI loaded image protocol GUID */
> > +5: .long 0x5B1B31A1
> > + .word 0x9562, 0x11d2
> > + .byte 0x8E, 0x3F, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B
> > + .previous
>
> Any reason for this not to live in .data (or .rodata)?
None other than laziness ...
> > #endif
> >
> > .code64
> > @@ -465,11 +510,23 @@ SYM_CODE_END(startup_64)
> > SYM_FUNC_START(efi64_stub_entry)
> > SYM_FUNC_START_ALIAS(efi_stub_entry)
> > and $~0xf, %rsp /* realign the stack */
> > +#ifdef CONFIG_EFI_MIXED
> > + cmpl $0, %edx
> > + jz 0f
> > +#endif
> > call efi_main
> > movq %rax,%rsi
> > movl BP_code32_start(%esi), %eax
> > leaq startup_64(%rax), %rax
> > jmp *%rax
> > +
> > +#ifdef CONFIG_EFI_MIXED
> > +0: movl %edi, %ecx // MS calling convention
> > + movl %esi, %edx
> > + call efi_pe_entry
> > +1: hlt
> > + jmp 1b
> > +#endif
> > SYM_FUNC_END(efi64_stub_entry)
> > SYM_FUNC_END_ALIAS(efi_stub_entry)
> > #endif
> > @@ -641,7 +698,7 @@ SYM_DATA_START_LOCAL(gdt)
> > SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
> >
> > #ifdef CONFIG_EFI_MIXED
> > -SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0)
> > +SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)
> > SYM_DATA(efi_is64, .byte 1)
> > #endif
> >
> > --
> > 2.17.1
> >
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next prev parent reply other threads:[~2020-02-13 17:42 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 14:59 [RFC PATCH 0/3] efi/x86: add support for generic EFI mixed mode boot Ard Biesheuvel
2020-02-13 14:59 ` [RFC PATCH 1/3] efi/x86: drop redundant .bss section Ard Biesheuvel
2020-02-13 14:59 ` [RFC PATCH 2/3] efi/x86: add true mixed mode entry point into .compat section Ard Biesheuvel
2020-02-13 16:59 ` Arvind Sankar
2020-02-13 17:13 ` Ard Biesheuvel
2020-02-13 14:59 ` [RFC PATCH 3/3] efi/x86: implement mixed mode boot without the handover protocol Ard Biesheuvel
2020-02-13 17:23 ` Arvind Sankar
2020-02-13 17:42 ` Ard Biesheuvel [this message]
2020-02-13 17:53 ` [RFC PATCH 0/3] efi/x86: add support for generic EFI mixed mode boot Arvind Sankar
2020-02-13 17:55 ` Ard Biesheuvel
2020-02-13 18:47 ` Arvind Sankar
2020-02-13 22:36 ` Ard Biesheuvel
2020-02-14 0:10 ` Arvind Sankar
2020-02-14 0:12 ` Arvind Sankar
2020-02-14 0:21 ` Ard Biesheuvel
2020-02-14 0:38 ` Arvind Sankar
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