[tip: objtool/urgent] objtool: Don't make .altinstructions writable

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     e31694e0a7a709293319475d8001e05e31f2178c
Gitweb:        https://git.kernel.org/tip/e31694e0a7a709293319475d8001e05e31f2178c
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Wed, 23 Jun 2021 10:42:28 -05:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 24 Jun 2021 08:55:20 +02:00

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@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/6c284ae89717889ea136f9f0064d914cd8329d31.1624462939.git.jpoimboe@xxxxxxxxxx
---
 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 523aa41..bc82105 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -684,7 +684,7 @@ 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");