From: Miroslav Benes mbenes@suse.cz
commit 2f62f36e62daec43aa7b9633ef7f18e042a80bed upstream.
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 Signed-off-by: Markus Boehme markubo@amazon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/xen/xen-head.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
--- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -35,7 +35,11 @@ ENTRY(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 @@ ENTRY(startup_xen) wrmsr #endif
- jmp xen_start_kernel + call xen_start_kernel END(startup_xen) __FINIT #endif