Commit c98a76ea authored Feb 26, 2020 by Arvind Sankar Committed by Ingo Molnar Feb 29, 2020

x86/boot/compressed: Fix reloading of GDTR post-relocation



The following commit:

  ef5a7b5e ("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.

A followup commit:

   32d00913 ("x86/boot: Reload GDTR after copying to the end of the buffer")

introduced a similar GDTR reload in the 64-bit kernel as well.

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.

Fixes: ef5a7b5e ("efi/x86: Remove GDT setup from efi_main")
Fixes: 32d00913 ("x86/boot: Reload GDTR after copying to the end of the buffer")
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Link: https://lore.kernel.org/r/20200226230031.3011645-2-nivedita@alum.mit.edu

parent 3e03dca5

arch/x86/boot/compressed/head_32.S

+4 −5

Original line number	Diff line number	Diff line
		@@ -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.

arch/x86/boot/compressed/head_64.S

+2 −2

Original line number	Diff line number	Diff line
		@@ -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)

		/*

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