Re: [PATCH 2/3] MODSIGN: Avoid using .incbin in C source

[Rusty Russell]

Michal Marek <mmarek@xxxxxxx> writes:
> It looks good, but looking at your patch, I just noticed that we have two
> versions of the SYMBOL_PREFIX macro in the kernel now:
>
> scripts/Makefile.lib has had since some time
>
> ifdef CONFIG_SYMBOL_PREFIX
> _sym_flags = -DSYMBOL_PREFIX=$(patsubst "%",%,$(CONFIG_SYMBOL_PREFIX))
> _cpp_flags += $(_sym_flags)
> _a_flags += $(_sym_flags)
> endif
>
> while include/linux/kernel.h now has
>
> /* This helps us to avoid #ifdef CONFIG_SYMBOL_PREFIX */
> #ifdef CONFIG_SYMBOL_PREFIX
> #define SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
> #else
> #define SYMBOL_PREFIX ""
> #endif

What a mess!  AFAICT there's one place which a non-string SYMBOL_PREFIX:
        include/asm-generic/vmlinux.lds.h

So we do need it, and the only sane way seems to be via the cmdline and
the shell usefully stripping quotes as we do.

So I just took Takashi's do-it-all-in-asm fix, and removed this
re-definition (we have the same thing, BTW, called
MODULE_SYMBOL_PREFIX).

I added a comment about the cmdline SYMBOL_PREFIX, too.

Thanks,
Rusty.

From: Takashi Iwai <tiwai@xxxxxxx>
Subject: MODSIGN: Avoid using .incbin in C source

Using the asm .incbin statement in C sources breaks any gcc wrapper which
assumes that preprocessed C source is self-contained. Use a separate .S
file to include the siging key and certificate.

[ This means we no longer need SYMBOL_PREFIX which is defined in kernel.h
  from cbdbf2abb7844548a7d7a6a2ae7af6b6fbcea401, so I removed it -- RR ]

Tested-by: Michal Marek <mmarek@xxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 7d8dfc7..a123b13 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -701,13 +701,6 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 #define COMPACTION_BUILD 0
 #endif
 
-/* This helps us to avoid #ifdef CONFIG_SYMBOL_PREFIX */
-#ifdef CONFIG_SYMBOL_PREFIX
-#define SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
-#else
-#define SYMBOL_PREFIX ""
-#endif
-
 /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 # define REBUILD_DUE_TO_FTRACE_MCOUNT_RECORD
diff --git a/kernel/Makefile b/kernel/Makefile
index 86e3285..0bd9d43 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -54,7 +54,7 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
 obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += module.o
-obj-$(CONFIG_MODULE_SIG) += module_signing.o modsign_pubkey.o
+obj-$(CONFIG_MODULE_SIG) += module_signing.o modsign_pubkey.o modsign_certificate.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o
@@ -139,7 +139,7 @@ ifeq ($(CONFIG_MODULE_SIG),y)
 extra_certificates:
 	touch $@
 
-kernel/modsign_pubkey.o: signing_key.x509 extra_certificates
+kernel/modsign_certificate.o: signing_key.x509 extra_certificates
 
 ###############################################################################
 #
diff --git a/kernel/modsign_certificate.S b/kernel/modsign_certificate.S
new file mode 100644
index 0000000..246b4c6
--- /dev/null
+++ b/kernel/modsign_certificate.S
@@ -0,0 +1,19 @@
+/* SYMBOL_PREFIX defined on commandline from CONFIG_SYMBOL_PREFIX */
+#ifndef SYMBOL_PREFIX
+#define ASM_SYMBOL(sym) sym
+#else
+#define PASTE2(x,y) x##y
+#define PASTE(x,y) PASTE2(x,y)
+#define ASM_SYMBOL(sym) PASTE(SYMBOL_PREFIX, sym)
+#endif
+
+#define GLOBAL(name)	\
+	.globl ASM_SYMBOL(name);	\
+	ASM_SYMBOL(name):
+
+	.section ".init.data","aw"
+
+GLOBAL(modsign_certificate_list)
+	.incbin "signing_key.x509"
+	.incbin "extra_certificates"
+GLOBAL(modsign_certificate_list_end)
diff --git a/kernel/modsign_pubkey.c b/kernel/modsign_pubkey.c
index 767e559..045504f 100644
--- a/kernel/modsign_pubkey.c
+++ b/kernel/modsign_pubkey.c
@@ -20,12 +20,6 @@ struct key *modsign_keyring;
 
 extern __initdata const u8 modsign_certificate_list[];
 extern __initdata const u8 modsign_certificate_list_end[];
-asm(".section .init.data,\"aw\"\n"
-    SYMBOL_PREFIX "modsign_certificate_list:\n"
-    ".incbin \"signing_key.x509\"\n"
-    ".incbin \"extra_certificates\"\n"
-    SYMBOL_PREFIX "modsign_certificate_list_end:"
-    );
 
 /*
  * We need to make sure ccache doesn't cache the .o file as it doesn't notice
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