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objtool/klp: Fix kCFI prefix finding/cloning

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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.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
This commit is contained in:
Josh Poimboeuf
2026-04-27 21:15:52 -07:00
parent fc0bb9915b
commit f7ceffd21a
1 changed files with 2 additions and 2 deletions
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4
tools/objtool/include/objtool/elf.h
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@@ -539,10 +539,10 @@ static inline struct symbol *get_func_prefix(struct symbol *func)
{
struct symbol *prev;
if (!is_func_sym(func))
if (!is_func_sym(func) || !func->offset)
return NULL;
prev = sec_prev_sym(func);
prev = find_func_containing(func->sec, func->offset - 1);
if (prev && is_prefix_func(prev))
return prev;