Commit 113d4bc9 authored Feb 17, 2020 by Josh Poimboeuf Committed by Borislav Petkov Feb 21, 2020

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@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/485
Link: https://lkml.kernel.org/r/263f6aae46d33da0b86d7030ced878cb5cab1788.1581997059.git.jpoimboe@redhat.com

parent dc419723

tools/objtool/check.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -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))
		continue;

		/* 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)
		continue;
		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