Re: [PATCH v2 51/53] objtool/klp: Fix kCFI prefix finding/cloning

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <[email protected]> wrote:
>
> With CFI+CALL_PADDING, Clang places .Ltmp labels at the start of the NOP
> padding (offset 5) between the __cfi_ prefix and the function entry
> point.  get_func_prefix() only checks the immediately previous symbol,
> so the intervening .Ltmp label causes it to miss the __cfi_ prefix
> symbol.
>
> This results in klp-diff not cloning the kCFI type hash into the
> livepatch module, causing a CFI failure at module load when calling
> callback functions through indirect calls:
>
>   CFI failure at __klp_enable_patch+0xab/0x140
>     (target: pre_patch_callback+0x0/0x80 [livepatch_combined];
>      expected type: 0xde073954)
>
> Instead of walking backward through the section's symbol list, just use
> find_func_containing() for the byte before the function.  This works now
> that __cfi_ symbols are being grown by objtool to fill the padding.
>
> Signed-off-by: Josh Poimboeuf <[email protected]>

Acked-by: Song Liu <[email protected]>