[PATCH v2 6/9] x86/kexec: Mark machine_kexec() with __nocfi

[David Woodhouse]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

A recent commit caused the relocate_kernel() function to be invoked
through a function pointer, but it does not have CFI information. The
resulting trap occurs after the IDT and GDT have been invalidated,
leading to a triple-fault if CONFIG_CFI_CLANG is enabled.

Using SYM_TYPED_FUNC_START() to provide the CFI information looks like
it will require a prolonged battle with objtool. And is fairly pointless
anyway, as the actual signature comes from a __kcfi_typeid_… symbol
emitted from the C code based on the function prototype it thinks that
relocate_kernel has, rendering the check somewhat tautological.

The simple fix is just to mark machine_kexec() with __nocfi.

Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Suggested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Fixes: eeebbde57113 ("x86/kexec: Invoke copy of relocate_kernel() instead of
the original")
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 arch/x86/kernel/machine_kexec_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 9232ad1562c8..1440f792a86d 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -342,7 +342,7 @@ void machine_kexec_cleanup(struct kimage *image)
  * Do not allocate memory (or fail in any way) in machine_kexec().
  * We are past the point of no return, committed to rebooting now.
  */
-void machine_kexec(struct kimage *image)
+void __nocfi machine_kexec(struct kimage *image)
 {
 	unsigned long (*relocate_kernel_ptr)(unsigned long indirection_page,
 					     unsigned long pa_control_page,
-- 
2.47.0