Commit 786a4575 authored by David Woodhouse's avatar David Woodhouse Committed by Borislav Petkov (AMD)
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x86/kexec: Push kjump return address even for non-kjump kexec 



The version of purgatory code shipped by kexec-tools attempts to look above
the top of its stack to find a return address for a kjump, even in a non-kjump
kexec.

After the commit in Fixes: the word above the stack might not be there,
leading to a fault (which is at least now caught by my exception-handling code
in kexec).

That commit fixed things for the actual kjump path, but no longer
"gratuitously" pushes the unused return address to the stack in the non-kjump
path. Put that *back* in the non-kjump path, to prevent purgatory from
crashing when trying to access it.

Fixes: 2cacf7f2 ("x86/kexec: Fix stack and handling of re-entry point for ::preserve_context")
Reported-by: default avatarRohan Kakulawaram <rohanka@google.com>
Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Acked-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Tested-by: default avatarRohan Kakulawaram <rohanka@google.com>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/32d627134143ffd957891cb697138e839c623211.camel@infradead.org
parent 5772f653

arch/x86/kernel/relocate_kernel_64.S

+8 −0
Original line number Diff line number Diff line
@@ -136,6 +136,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) 
	 * %r13 original CR4 when relocate_kernel() was invoked

	 */



	/*

	 * Set return address to 0 if not preserving context. The purgatory

	 * shipped in kexec-tools will unconditionally look for the return

	 * address on the stack and set a kexec_jump_back_entry= command

	 * line option if it's non-zero. There's no other way that it can

	 * tell a preserve-context (kjump) kexec from a normal one.

	 */

	pushq	$0

	/* store the start address on the stack */

	pushq   %rdx