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Subject[tip:core/urgent] objtool: Detect RIP-relative switch table references
Commit-ID:  6f5ec2993b1f39aed12fa6fd56e8dc2272ee8a33
Gitweb: https://git.kernel.org/tip/6f5ec2993b1f39aed12fa6fd56e8dc2272ee8a33
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Mon, 14 May 2018 08:53:24 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 15 May 2018 07:30:59 +0200

objtool: Detect RIP-relative switch table references

Typically a switch table can be found by detecting a .rodata access
followed an indirect jump:

1969: 4a 8b 0c e5 00 00 00 mov 0x0(,%r12,8),%rcx
1970: 00
196d: R_X86_64_32S .rodata+0x438
1971: e9 00 00 00 00 jmpq 1976 <dispc_runtime_suspend+0xb6a>
1972: R_X86_64_PC32 __x86_indirect_thunk_rcx-0x4

Randy Dunlap reported a case (seen with GCC 4.8) where the .rodata
access uses RIP-relative addressing:

19bd: 48 8b 3d 00 00 00 00 mov 0x0(%rip),%rdi # 19c4 <dispc_runtime_suspend+0xbb8>
19c0: R_X86_64_PC32 .rodata+0x45c
19c4: e9 00 00 00 00 jmpq 19c9 <dispc_runtime_suspend+0xbbd>
19c5: R_X86_64_PC32 __x86_indirect_thunk_rdi-0x4

In this case the relocation addend needs to be adjusted accordingly in
order to find the location of the switch table.

The fix is for case 3 (as described in the comments), but also make the
existing case 1 & 2 checks more precise by only adjusting the addend for
R_X86_64_PC32 relocations.

This fixes the following warnings:

drivers/video/fbdev/omap2/omapfb/dss/dispc.o: warning: objtool: dispc_runtime_suspend()+0xbb8: sibling call from callable instruction with modified stack frame
drivers/video/fbdev/omap2/omapfb/dss/dispc.o: warning: objtool: dispc_runtime_resume()+0xcc5: sibling call from callable instruction with modified stack frame

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/b6098294fd67afb69af8c47c9883d7a68bf0f8ea.1526305958.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
tools/objtool/check.c | 33 ++++++++++++++++++---------------
1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9bb04fddd3c8..f4bbce838433 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -903,24 +903,24 @@ static struct rela *find_switch_table(struct objtool_file *file,
{
struct rela *text_rela, *rodata_rela;
struct instruction *orig_insn = insn;
+ unsigned long table_offset;

+ /* case 1 & 2 */
text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
if (text_rela && text_rela->sym == file->rodata->sym &&
!find_symbol_containing(file->rodata, text_rela->addend)) {

- /* case 1 */
- rodata_rela = find_rela_by_dest(file->rodata,
- text_rela->addend);
- if (rodata_rela)
- return rodata_rela;
+ table_offset = text_rela->addend;
+ if (text_rela->type == R_X86_64_PC32) {
+ /* case 2 */
+ table_offset += 4;
+ file->ignore_unreachables = true;
+ }

- /* case 2 */
- rodata_rela = find_rela_by_dest(file->rodata,
- text_rela->addend + 4);
+ rodata_rela = find_rela_by_dest(file->rodata, table_offset);
if (!rodata_rela)
return NULL;

- file->ignore_unreachables = true;
return rodata_rela;
}

@@ -954,18 +954,21 @@ static struct rela *find_switch_table(struct objtool_file *file,
if (!text_rela || text_rela->sym != file->rodata->sym)
continue;

+ table_offset = text_rela->addend;
+ if (text_rela->type == R_X86_64_PC32)
+ table_offset += 4;
+
/*
* Make sure the .rodata address isn't associated with a
* symbol. gcc jump tables are anonymous data.
*/
- if (find_symbol_containing(file->rodata, text_rela->addend))
- continue;
-
- rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend);
- if (!rodata_rela)
+ if (find_symbol_containing(file->rodata, table_offset))
continue;

- return rodata_rela;
+ /* mov [rodata addr], %reg */
+ rodata_rela = find_rela_by_dest(file->rodata, table_offset);
+ if (rodata_rela)
+ return rodata_rela;
}

return NULL;
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