linux-kernel - [PATCH] x86, relocs: add more per-cpu gold special cases

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Message-ID: <20131001192203.GA29794@www.outflux.net>
Date:	Tue, 1 Oct 2013 12:22:04 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Cong Ding <dinggnu@...il.com>
Subject: [PATCH] x86, relocs: add more per-cpu gold special cases

The "gold" linker doesn't seem to put some additional per-cpu cases in
the right place. Add these to the per-cpu check. Without this, the kASLR
patch series fails to correctly apply relocations, and fails to boot.

Found and fixed by Michael Davidson.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/tools/relocs.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index f7bab68..71a2533 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -722,15 +722,23 @@ static void percpu_init(void)
 
 /*
  * Check to see if a symbol lies in the .data..percpu section.
- * For some as yet not understood reason the "__init_begin"
- * symbol which immediately preceeds the .data..percpu section
- * also shows up as it it were part of it so we do an explict
- * check for that symbol name and ignore it.
+ *
+ * The linker incorrectly associates some symbols with the
+ * .data..percpu section so we also need to check the symbol
+ * name to make sure that we classify the symbol correctly.
+ *
+ * The GNU linker incorrectly associates:
+ *	__init_begin
+ *
+ * The "gold" linker incorrectly associates:
+ *	init_per_cpu__irq_stack_union
+ *	init_per_cpu__gdt_page
  */
 static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
 {
 	return (sym->st_shndx == per_cpu_shndx) &&
-		strcmp(symname, "__init_begin");
+		strcmp(symname, "__init_begin") &&
+		strncmp(symname, "init_per_cpu_", 13);
 }
 
 
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security
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