[tip: x86/core] objtool: Skip magical retpoline .altinstr_replacement

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     68a59124f4c6363de619fea63231a97dd220a12c
Gitweb:        https://git.kernel.org/tip/68a59124f4c6363de619fea63231a97dd220a12c
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Fri, 26 Mar 2021 16:12:14 +01:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Thu, 01 Apr 2021 13:29:40 +02:00

objtool: Skip magical retpoline .altinstr_replacement

When the .altinstr_replacement is a retpoline, skip the alternative.
We already special case retpolines anyway.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Link: https://lkml.kernel.org/r/20210326151300.259429287@xxxxxxxxxxxxx
---
 tools/objtool/special.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index 2c7fbda..07b21cf 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -106,6 +106,14 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
 			return -1;
 		}
 
+		/*
+		 * Skip retpoline .altinstr_replacement... we already rewrite the
+		 * instructions for retpolines anyway, see arch_is_retpoline()
+		 * usage in add_{call,jump}_destinations().
+		 */
+		if (arch_is_retpoline(new_reloc->sym))
+			return 1;
+
 		alt->new_sec = new_reloc->sym->sec;
 		alt->new_off = (unsigned int)new_reloc->addend;
 
@@ -154,7 +162,9 @@ int special_get_alts(struct elf *elf, struct list_head *alts)
 			memset(alt, 0, sizeof(*alt));
 
 			ret = get_alt_entry(elf, entry, sec, idx, alt);
-			if (ret)
+			if (ret > 0)
+				continue;
+			if (ret < 0)
 				return ret;
 
 			list_add_tail(&alt->list, alts);