Commit 2f62f36e authored Mar 26, 2020 by Miroslav Benes Committed by Juergen Gross Mar 30, 2020

x86/xen: Make the boot CPU idle task reliable



The unwinder reports the boot CPU idle task's stack on XEN PV as
unreliable, which affects at least live patching. There are two reasons
for this. First, the task does not follow the x86 convention that its
stack starts at the offset right below saved pt_regs. It allows the
unwinder to easily detect the end of the stack and verify it. Second,
startup_xen() function does not store the return address before jumping
to xen_start_kernel() which confuses the unwinder.

Amend both issues by moving the starting point of initial stack in
startup_xen() and storing the return address before the jump, which is
exactly what call instruction does.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

parent 69086bd6

arch/x86/xen/xen-head.S

+6 −2

Original line number	Diff line number	Diff line
		@@ -35,7 +35,11 @@ SYM_CODE_START(startup_xen)
		rep __ASM_SIZE(stos)

		mov %_ASM_SI, xen_start_info
		mov $init_thread_union+THREAD_SIZE, %_ASM_SP
		#ifdef CONFIG_X86_64
		mov initial_stack(%rip), %rsp
		#else
		mov pa(initial_stack), %esp
		#endif

		#ifdef CONFIG_X86_64
		/* Set up %gs.
		@@ -51,7 +55,7 @@ SYM_CODE_START(startup_xen)
		wrmsr
		#endif

		jmp xen_start_kernel
		call xen_start_kernel
		SYM_CODE_END(startup_xen)
		__FINIT
		#endif

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