linux-kernel - [PATCH 5.10 098/390] objtool: Preserve special st_shndx indexes in elf_update

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Message-Id: <20221024113026.825316947@linuxfoundation.org>
Date:   Mon, 24 Oct 2022 13:28:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sami Tolvanen <samitolvanen@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 098/390] objtool: Preserve special st_shndx indexes in elf_update_symbol

From: Sami Tolvanen <samitolvanen@...gle.com>

[ Upstream commit 5141d3a06b2da1731ac82091298b766a1f95d3d8 ]

elf_update_symbol fails to preserve the special st_shndx values
between [SHN_LORESERVE, SHN_HIRESERVE], which results in it
converting SHN_ABS entries into SHN_UNDEF, for example. Explicitly
check for the special indexes and ensure these symbols are not
marked undefined.

Fixes: ead165fa1042 ("objtool: Fix symbol creation")
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-17-samitolvanen@google.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/objtool/elf.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 5aa3b4e76479..a2ea3931e01d 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -578,6 +578,11 @@ static int elf_update_symbol(struct elf *elf, struct section *symtab,
 	Elf64_Xword entsize = symtab->sh.sh_entsize;
 	int max_idx, idx = sym->idx;
 	Elf_Scn *s, *t = NULL;
+	bool is_special_shndx = sym->sym.st_shndx >= SHN_LORESERVE &&
+				sym->sym.st_shndx != SHN_XINDEX;
+
+	if (is_special_shndx)
+		shndx = sym->sym.st_shndx;
 
 	s = elf_getscn(elf->elf, symtab->idx);
 	if (!s) {
@@ -663,7 +668,7 @@ static int elf_update_symbol(struct elf *elf, struct section *symtab,
 	}
 
 	/* setup extended section index magic and write the symbol */
-	if (shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) {
+	if ((shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) || is_special_shndx) {
 		sym->sym.st_shndx = shndx;
 		if (!shndx_data)
 			shndx = 0;
-- 
2.35.1