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| author |  Ard Biesheuvel <ardb@kernel.org>
| 2023-08-07 18:27:03 +0200 |
|---|---|---|
| committer |  Borislav Petkov (AMD) <bp@alien8.de>
| 2023-08-07 20:40:36 +0200 |
| commit | d7156b986d4cc0657fa6dc05c9fcf51c3d55a0fe (patch) | |
| tree | 9810091771de88189b6be31a3a3f79c9fc1c9cc3 /arch/x86/boot | |
| parent | x86/decompressor: Avoid magic offsets for EFI handover entrypoint (diff) | |
| download | linux-d7156b986d4cc0657fa6dc05c9fcf51c3d55a0fe.tar.gz linux-d7156b986d4cc0657fa6dc05c9fcf51c3d55a0fe.tar.bz2 linux-d7156b986d4cc0657fa6dc05c9fcf51c3d55a0fe.zip | |
x86/efistub: Clear BSS in EFI handover protocol entrypoint
The so-called EFI handover protocol is value-add from the distros that
permits a loader to simply copy a PE kernel image into memory and call
an alternative entrypoint that is described by an embedded boot_params
structure.
Most implementations of this protocol do not bother to check the PE
header for minimum alignment, section placement, etc, and therefore also
don't clear the image's BSS, or even allocate enough memory for it.
Allocating more memory on the fly is rather difficult, but at least
clear the BSS region explicitly when entering in this manner, so that
the EFI stub code does not get confused by global variables that were
not zero-initialized correctly.
When booting in mixed mode, this BSS clearing must occur before any
global state is created, so clear it in the 32-bit asm entry point.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-7-ardb@kernel.org
Diffstat (limited to 'arch/x86/boot')
| -rw-r--r-- | arch/x86/boot/compressed/efi_mixed.S | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compressed/efi_mixed.S index 9308b595f6f0..8a02a151806d 100644 --- a/arch/x86/boot/compressed/efi_mixed.S +++ b/arch/x86/boot/compressed/efi_mixed.S @@ -142,6 +142,18 @@ SYM_FUNC_END(__efi64_thunk) .code32 #ifdef CONFIG_EFI_HANDOVER_PROTOCOL SYM_FUNC_START(efi32_stub_entry) + call 1f +1: popl %ecx + + /* Clear BSS */ + xorl %eax, %eax + leal (_bss - 1b)(%ecx), %edi + leal (_ebss - 1b)(%ecx), %ecx + subl %edi, %ecx + shrl $2, %ecx + cld + rep stosl + add $0x4, %esp /* Discard return address */ popl %ecx popl %edx @@ -334,7 +346,7 @@ SYM_FUNC_END(efi32_pe_entry) .org efi32_stub_entry + 0x200 .code64 SYM_FUNC_START_NOALIGN(efi64_stub_entry) - jmp efi_stub_entry + jmp efi_handover_entry SYM_FUNC_END(efi64_stub_entry) #endif |