[tip: core/objtool] objtool: Fix clang switch table edge case

From: tip-bot2 for Josh Poimboeuf
Date: Fri Feb 21 2020 - 04:51:03 EST

The following commit has been merged into the core/objtool branch of tip:

Commit-ID: 113d4bc9048336ba7c3d2ad972dbad4aef6e148a
Gitweb: https://git.kernel.org/tip/113d4bc9048336ba7c3d2ad972dbad4aef6e148a
Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Mon, 17 Feb 2020 21:41:53 -06:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 21 Feb 2020 10:12:52 +01:00

objtool: Fix clang switch table edge case

Clang has the ability to create a switch table which is not a jump
table, but is rather a table of string pointers. This confuses objtool,
because it sees the relocations for the string pointers and assumes
they're part of a jump table:

drivers/ata/sata_dwc_460ex.o: warning: objtool: sata_dwc_bmdma_start_by_tag()+0x3a2: can't find switch jump table
net/ceph/messenger.o: warning: objtool: ceph_con_workfn()+0x47c: can't find switch jump table

Make objtool's find_jump_table() smart enough to distinguish between a
switch jump table (which has relocations to text addresses in the same
function as the original instruction) and other anonymous rodata (which
may have relocations to elsewhere).

Reported-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/485
Link: https://lkml.kernel.org/r/263f6aae46d33da0b86d7030ced878cb5cab1788.1581997059.git.jpoimboe@xxxxxxxxxx
tools/objtool/check.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b038de2..4d6e283 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1025,7 +1025,7 @@ static struct rela *find_jump_table(struct objtool_file *file,
struct instruction *insn)
struct rela *text_rela, *table_rela;
- struct instruction *orig_insn = insn;
+ struct instruction *dest_insn, *orig_insn = insn;
struct section *table_sec;
unsigned long table_offset;

@@ -1077,10 +1077,17 @@ static struct rela *find_jump_table(struct objtool_file *file,
strcmp(table_sec->name, C_JUMP_TABLE_SECTION))

- /* Each table entry has a rela associated with it. */
+ /*
+ * Each table entry has a rela associated with it. The rela
+ * should reference text in the same function as the original
+ * instruction.
+ */
table_rela = find_rela_by_dest(table_sec, table_offset);
if (!table_rela)
+ dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
+ if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
+ continue;

* Use of RIP-relative switch jumps is quite rare, and