From 32d009137a5646947d450da6fa641a1f4dc1e42c Mon Sep 17 00:00:00 2001 From: Arvind Sankar Date: Sun, 2 Feb 2020 12:13:49 -0500 Subject: [PATCH] x86/boot: Reload GDTR after copying to the end of the buffer The GDT may get overwritten during the copy or during extract_kernel, which will cause problems if any segment register is touched before the GDTR is reloaded by the decompressed kernel. For safety update the GDTR to point to the GDT within the copied kernel. Signed-off-by: Arvind Sankar Link: https://lore.kernel.org/r/20200202171353.3736319-4-nivedita@alum.mit.edu Signed-off-by: Ard Biesheuvel --- arch/x86/boot/compressed/head_64.S | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index c56b30b..27eb2a6 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -439,6 +439,16 @@ trampoline_return: cld popq %rsi + /* + * 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. + */ + leaq gdt64(%rbx), %rax + subq %rbp, 2(%rax) + addq %rbx, 2(%rax) + lgdt (%rax) + /* * Jump to the relocated address. */ -- 2.7.4