linux-hardening - [PATCH v2] objtool: Report section name in elf_init_reloc_text

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Date: Mon,  6 May 2024 08:55:54 -0700
From: Kees Cook <keescook@...omium.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH v2] objtool: Report section name in elf_init_reloc_text_sym() warning

While tracking down issues with LKDTM's .rodata "function", I found
the warning from elf_init_reloc_text_sym() to be unhelpful because it
wasn't clear which calling path it was coming from. Report the sec->name
and rephrase the warning a bit. Additionally check for NULL sym->name,
which may happen.

Before:

vmlinux.o: warning: objtool: bad call to elf_init_reloc_text_sym() for data symbol .rodata

After:

vmlinux.o: warning: objtool: .cfi_sites: unexpected reference to non-executable symbol '.rodata'

Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
 v1: https://lore.kernel.org/lkml/20240430235106.work.680-kees@kernel.org/
---
 tools/objtool/elf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 3d27983dc908..b38cedd4fd55 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -891,8 +891,8 @@ struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec,
 	int addend = insn_off;
 
 	if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) {
-		WARN("bad call to %s() for data symbol %s",
-		     __func__, sym->name);
+		WARN("%s: unexpected reference to non-executable symbol '%s'",
+		     sec->name, sym->name ?: "<unknown>");
 		return NULL;
 	}
 
-- 
2.34.1