linux-kernel - [PATCH 2/2] objtool/x86: Fix elf_add

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Date:   Wed, 12 May 2021 19:42:13 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Miroslav Benes <mbenes@...e.cz>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] objtool/x86: Fix elf_add_alternative() endianness

Currently x86 kernel cross-compiled on big endian system fails at boot with:
kernel BUG at arch/x86/kernel/alternative.c:258!

Corresponding bug condition look like the following:
BUG_ON(feature >= (NCAPINTS + NBUGINTS) * 32);

Fix that by converting alternative feature/cpuid to target endianness.

Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls")
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
---
 tools/objtool/arch/x86/decode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index cedf3ede7545..24295d39713b 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -19,6 +19,7 @@
 #include <objtool/elf.h>
 #include <objtool/arch.h>
 #include <objtool/warn.h>
+#include <objtool/endianness.h>
 #include <arch/elf.h>
 
 static int is_x86_64(const struct elf *elf)
@@ -725,7 +726,7 @@ static int elf_add_alternative(struct elf *elf,
 		return -1;
 	}
 
-	alt->cpuid = cpuid;
+	alt->cpuid = bswap_if_needed(cpuid);
 	alt->instrlen = orig_len;
 	alt->replacementlen = repl_len;
 
-- 
2.25.4