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@xxxxxxxxxx> > --- > 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. > 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)? > #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 >
