Messages in this thread Patch in this message | | | From | Arvind Sankar <> | Subject | [PATCH v2 1/1] x86/boot/compressed: Fix reloading of GDTR post-relocation | Date | Wed, 26 Feb 2020 18:00:31 -0500 |
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Commit ef5a7b5eb13e ("efi/x86: Remove GDT setup from efi_main") introduced GDT setup into the 32-bit kernel's startup_32, and reloads the GDTR after relocating the kernel for paranoia's sake.
Commit 32d009137a56 ("x86/boot: Reload GDTR after copying to the end of the buffer") introduced a similar GDTR reload in the 64-bit kernel.
The GDTR is adjusted by init_size - _end, however this may not be the correct offset to apply if the kernel was loaded at a misaligned address or below LOAD_PHYSICAL_ADDR, as in that case the decompression buffer has an additional offset from the original load address.
This should never happen for a conformant bootloader, but we're being paranoid anyway, so just store the new GDT address in there instead of adding any offsets, which is simpler as well.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> Fixes: ef5a7b5eb13e ("efi/x86: Remove GDT setup from efi_main") Fixes: 32d009137a56 ("x86/boot: Reload GDTR after copying to the end of the buffer") --- arch/x86/boot/compressed/head_32.S | 9 ++++----- arch/x86/boot/compressed/head_64.S | 4 ++-- 2 files changed, 6 insertions(+), 7 deletions(-)
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S index 356060c5332c..2f8138b71ea9 100644 --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -139,12 +139,11 @@ SYM_FUNC_START(startup_32) /* * The GDT may get overwritten either during the copy we just did or * during extract_kernel below. To avoid any issues, repoint the GDTR - * to the new copy of the GDT. EAX still contains the previously - * calculated relocation offset of init_size - _end. + * to the new copy of the GDT. */ - leal gdt(%ebx), %edx - addl %eax, 2(%edx) - lgdt (%edx) + leal gdt(%ebx), %eax + movl %eax, 2(%eax) + lgdt (%eax) /* * Jump to the relocated address. diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index f7bacc4c1494..fcf8feaa57ea 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -456,8 +456,8 @@ trampoline_return: * to the new copy of the GDT. */ leaq gdt64(%rbx), %rax - subq %rbp, 2(%rax) - addq %rbx, 2(%rax) + leaq gdt(%rbx), %rdx + movq %rdx, 2(%rax) lgdt (%rax) /* -- 2.24.1
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