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Commit 5c9b0b1c authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Ingo Molnar
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x86/boot/compressed/64: Set up GOT for paging_prepare() and cleanup_trampoline() 

Eric and Hugh have reported instant reboot due to my recent changes in
decompression code.

The root cause is that I didn't realize that we need to adjust GOT to be
able to run C code that early.

The problem is only visible with an older toolchain. Binutils >= 2.24 is
able to eliminate GOT references by replacing them with RIP-relative
address loads:

  https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=80d873266dec



We need to adjust GOT two times:

 - before calling paging_prepare() using the initial load address
 - before calling C code from the relocated kernel

Reported-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Reported-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 194a9749 ("x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G")
Link: http://lkml.kernel.org/r/20180516080131.27913-2-kirill.shutemov@linux.intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 2fa9d1cf

arch/x86/boot/compressed/head_64.S

+55 −13
Original line number Diff line number Diff line
@@ -305,6 +305,25 @@ ENTRY(startup_64) 
	/* Set up the stack */

	leaq	boot_stack_end(%rbx), %rsp



	/*

	 * paging_prepare() and cleanup_trampoline() below can have GOT

	 * references. Adjust the table with address we are running at.

	 *

	 * Zero RAX for adjust_got: the GOT was not adjusted before;

	 * there's no adjustment to undo.

	 */

	xorq	%rax, %rax



	/*

	 * Calculate the address the binary is loaded at and use it as

	 * a GOT adjustment.

	 */

	call	1f

1:	popq	%rdi

	subq	$1b, %rdi



	call	adjust_got



	/*

	 * At this point we are in long mode with 4-level paging enabled,

	 * but we might want to enable 5-level paging or vice versa.
@@ -381,6 +400,21 @@ trampoline_return: 
	pushq	$0

	popfq



	/*

	 * Previously we've adjusted the GOT with address the binary was

	 * loaded at. Now we need to re-adjust for relocation address.

	 *

	 * Calculate the address the binary is loaded at, so that we can

	 * undo the previous GOT adjustment.

	 */

	call	1f

1:	popq	%rax

	subq	$1b, %rax



	/* The new adjustment is the relocation address */

	movq	%rbx, %rdi

	call	adjust_got



/*

 * Copy the compressed kernel to the end of our buffer

 * where decompression in place becomes safe.
@@ -481,19 +515,6 @@ relocated: 
	shrq	$3, %rcx

	rep	stosq



/*

 * Adjust our own GOT

 */

	leaq	_got(%rip), %rdx

	leaq	_egot(%rip), %rcx

1:

	cmpq	%rcx, %rdx

	jae	2f

	addq	%rbx, (%rdx)

	addq	$8, %rdx

	jmp	1b

2:

	

/*

 * Do the extraction, and jump to the new kernel..

 */
@@ -512,6 +533,27 @@ relocated: 
 */

	jmp	*%rax



/*

 * Adjust the global offset table

 *

 * RAX is the previous adjustment of the table to undo (use 0 if it's the

 * first time we touch GOT).

 * RDI is the new adjustment to apply.

 */

adjust_got:

	/* Walk through the GOT adding the address to the entries */

	leaq	_got(%rip), %rdx

	leaq	_egot(%rip), %rcx

1:

	cmpq	%rcx, %rdx

	jae	2f

	subq	%rax, (%rdx)	/* Undo previous adjustment */

	addq	%rdi, (%rdx)	/* Apply the new adjustment */

	addq	$8, %rdx

	jmp	1b

2:

	ret



	.code32

/*

 * This is the 32-bit trampoline that will be copied over to low memory.