linux-kernel - [PATCH] objtool: Don't make .altinstructions writable

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Message-Id: <6c284ae89717889ea136f9f0064d914cd8329d31.1624462939.git.jpoimboe@redhat.com>
Date:   Wed, 23 Jun 2021 10:42:28 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org, Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>
Subject: [PATCH] objtool: Don't make .altinstructions writable

When objtool creates the .altinstructions section, it sets the SHF_WRITE
flag to make the section writable -- unless the section had already been
previously created by the kernel.  The mismatch between kernel-created
and objtool-created section flags can cause failures with external
tooling (kpatch-build).  And the section doesn't need to be writable
anyway.

Make the section flags consistent with the kernel's.

Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls")
Reported-by: Joe Lawrence <joe.lawrence@...hat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/arch/x86/decode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index cedf3ede7545..32b2739f6115 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -683,7 +683,7 @@ static int elf_add_alternative(struct elf *elf,
 	sec = find_section_by_name(elf, ".altinstructions");
 	if (!sec) {
 		sec = elf_create_section(elf, ".altinstructions",
-					 SHF_WRITE, size, 0);
+					 SHF_ALLOC, size, 0);
 
 		if (!sec) {
 			WARN_ELF("elf_create_section");
-- 
2.31.1