Re: [PATCH v7 0/8] x86/kexec: Add exception handling for relocate_kernel

[David Woodhouse]

On Thu, 2025-03-13 at 19:58 +0000, David Woodhouse wrote:
> 
> Reproduced that by going back to x86-64 defconfig. 

Turns out the unret check doesn't even run unless CONFIG_DEBUG_ENTRY is
enabled (which enables CONFIG_NOINSTR_VALIDATION and thus runs objtool
on vmlinux.o). Which is why I didn't see it.

> vmlinux.o: warning: objtool: exc_handler+0xe: early indirect call

With Peter's help (thanks), this is fixed by adding VALIDATE_UNRET_END.
I'll squash this into the next posting:

--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -481,6 +481,9 @@ SYM_CODE_START_NOALIGN(kexec_debug_exc_vectors)
 SYM_CODE_END(kexec_debug_exc_vectors)
 
 SYM_CODE_START_LOCAL_NOALIGN(exc_handler)
+       /* No need for ret mitigations during kexec */
+       VALIDATE_UNRET_END
+
        pushq   %rax
        pushq   %rbx
        pushq   %rcx

Attachment: smime.p7s
Description: S/MIME cryptographic signature