diff options
author | Ard Biesheuvel <ardb@kernel.org> | 2023-08-07 19:27:20 +0300 |
---|---|---|
committer | Borislav Petkov (AMD) <bp@alien8.de> | 2023-08-07 22:07:43 +0300 |
commit | a1b87d54f4e45ff5e0d081fb1d9db3bf1a8fb39a (patch) | |
tree | 6bd9f612cbdffe11bfcb1c023aaa02f56654ed9a /arch/x86/boot/compressed/efi_mixed.S | |
parent | 31c77a50992e8dd136feed7b67073bb5f1f978cc (diff) | |
download | linux-a1b87d54f4e45ff5e0d081fb1d9db3bf1a8fb39a.tar.xz |
x86/efistub: Avoid legacy decompressor when doing EFI boot
The bare metal decompressor code was never really intended to run in a
hosted environment such as the EFI boot services, and does a few things
that are becoming problematic in the context of EFI boot now that the
logo requirements are getting tighter: EFI executables will no longer be
allowed to consist of a single executable section that is mapped with
read, write and execute permissions if they are intended for use in a
context where Secure Boot is enabled (and where Microsoft's set of
certificates is used, i.e., every x86 PC built to run Windows).
To avoid stepping on reserved memory before having inspected the E820
tables, and to ensure the correct placement when running a kernel build
that is non-relocatable, the bare metal decompressor moves its own
executable image to the end of the allocation that was reserved for it,
in order to perform the decompression in place. This means the region in
question requires both write and execute permissions, which either need
to be given upfront (which EFI will no longer permit), or need to be
applied on demand using the existing page fault handling framework.
However, the physical placement of the kernel is usually randomized
anyway, and even if it isn't, a dedicated decompression output buffer
can be allocated anywhere in memory using EFI APIs when still running in
the boot services, given that EFI support already implies a relocatable
kernel. This means that decompression in place is never necessary, nor
is moving the compressed image from one end to the other.
Since EFI already maps all of memory 1:1, it is also unnecessary to
create new page tables or handle page faults when decompressing the
kernel. That means there is also no need to replace the special
exception handlers for SEV. Generally, there is little need to do
any of the things that the decompressor does beyond
- initialize SEV encryption, if needed,
- perform the 4/5 level paging switch, if needed,
- decompress the kernel
- relocate the kernel
So do all of this from the EFI stub code, and avoid the bare metal
decompressor altogether.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-24-ardb@kernel.org
Diffstat (limited to 'arch/x86/boot/compressed/efi_mixed.S')
-rw-r--r-- | arch/x86/boot/compressed/efi_mixed.S | 55 |
1 files changed, 0 insertions, 55 deletions
diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compressed/efi_mixed.S index 8a02a151806d..f4e22ef774ab 100644 --- a/arch/x86/boot/compressed/efi_mixed.S +++ b/arch/x86/boot/compressed/efi_mixed.S @@ -269,10 +269,6 @@ SYM_FUNC_START_LOCAL(efi32_entry) jmp startup_32 SYM_FUNC_END(efi32_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) - /* * efi_status_t efi32_pe_entry(efi_handle_t image_handle, * efi_system_table_32_t *sys_table) @@ -280,8 +276,6 @@ SYM_FUNC_END(efi32_entry) SYM_FUNC_START(efi32_pe_entry) pushl %ebp movl %esp, %ebp - pushl %eax // dummy push to allocate loaded_image - pushl %ebx // save callee-save registers pushl %edi @@ -290,48 +284,8 @@ SYM_FUNC_START(efi32_pe_entry) movl $0x80000003, %eax // EFI_UNSUPPORTED jnz 2f - call 1f -1: pop %ebx - - /* Get the loaded image protocol pointer from the image handle */ - leal -4(%ebp), %eax - pushl %eax // &loaded_image - leal (loaded_image_proto - 1b)(%ebx), %eax - pushl %eax // pass the GUID address - pushl 8(%ebp) // pass the image handle - - /* - * Note the alignment of the stack frame. - * sys_table - * handle <-- 16-byte aligned on entry by ABI - * return address - * frame pointer - * loaded_image <-- local variable - * saved %ebx <-- 16-byte aligned here - * saved %edi - * &loaded_image - * &loaded_image_proto - * handle <-- 16-byte aligned for call to handle_protocol - */ - - movl 12(%ebp), %eax // sys_table - movl ST32_boottime(%eax), %eax // sys_table->boottime - call *BS32_handle_protocol(%eax) // sys_table->boottime->handle_protocol - addl $12, %esp // restore argument space - testl %eax, %eax - jnz 2f - movl 8(%ebp), %ecx // image_handle movl 12(%ebp), %edx // sys_table - movl -4(%ebp), %esi // loaded_image - movl LI32_image_base(%esi), %esi // loaded_image->image_base - leal (startup_32 - 1b)(%ebx), %ebp // runtime address of startup_32 - /* - * 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, %ebp // calculate image_offset - movl %ebp, (image_offset - 1b)(%ebx) // save image_offset xorl %esi, %esi jmp efi32_entry // pass %ecx, %edx, %esi // no other registers remain live @@ -350,15 +304,6 @@ SYM_FUNC_START_NOALIGN(efi64_stub_entry) SYM_FUNC_END(efi64_stub_entry) #endif - .section ".rodata" - /* EFI loaded image protocol GUID */ - .balign 4 -SYM_DATA_START_LOCAL(loaded_image_proto) - .long 0x5b1b31a1 - .word 0x9562, 0x11d2 - .byte 0x8e, 0x3f, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b -SYM_DATA_END(loaded_image_proto) - .data .balign 8 SYM_DATA_START_LOCAL(efi32_boot_gdt) |