debug: Fix WARN_ON_ONCE() for modules

Mike Galbraith reported a situation where a WARN_ON_ONCE() call in DRM
code turned into an oops.  As it turns out, WARN_ON_ONCE() seems to be
completely broken when called from a module.

The bug was introduced with the following commit:

  19d436268dde ("debug: Add _ONCE() logic to report_bug()")

That commit changed WARN_ON_ONCE() to move its 'once' logic into the bug
trap handler.  It requires a writable bug table so that the BUGFLAG_DONE
bit can be written to the flags to indicate the first warning has
occurred.

The bug table was made writable for vmlinux, which relies on
vmlinux.lds.S and vmlinux.lds.h for laying out the sections.  However,
it wasn't made writable for modules, which rely on the ELF section
header flags.

Reported-by: Mike Galbraith <efault@gmx.de>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 19d436268dde ("debug: Add _ONCE() logic to report_bug()")
Link: http://lkml.kernel.org/r/a53b04235a65478dd9afc51f5b329fdc65c84364.1500095401.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

9 files changed, 18 insertions, 18 deletions

diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index 4e6e88a6b2f4..2244a94ed9c9 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -37,7 +37,7 @@ do {								\
 		".pushsection .rodata.str, \"aMS\", %progbits, 1\n" \
 		"2:\t.asciz " #__file "\n" 			\
 		".popsection\n" 				\
-		".pushsection __bug_table,\"a\"\n"		\
+		".pushsection __bug_table,\"aw\"\n"		\
 		".align 2\n"					\
 		"3:\t.word 1b, 2b\n"				\
 		"\t.hword " #__line ", 0\n"			\
diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
index 366448eb0fb7..a02a57186f56 100644
--- a/arch/arm64/include/asm/bug.h
+++ b/arch/arm64/include/asm/bug.h
@@ -36,7 +36,7 @@
 #ifdef CONFIG_GENERIC_BUG
 
 #define __BUG_ENTRY(flags) 				\
-		".pushsection __bug_table,\"a\"\n\t"	\
+		".pushsection __bug_table,\"aw\"\n\t"	\
 		".align 2\n\t"				\
 	"0:	.long 1f - 0b\n\t"			\
 _BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
diff --git a/arch/blackfin/include/asm/bug.h b/arch/blackfin/include/asm/bug.h
index 8d9b1eba89c4..76b2e82ee730 100644
--- a/arch/blackfin/include/asm/bug.h
+++ b/arch/blackfin/include/asm/bug.h
@@ -21,7 +21,7 @@
 #define _BUG_OR_WARN(flags)						\
 	asm volatile(							\
 		"1:	.hword	%0\n"					\
-		"	.section __bug_table,\"a\",@progbits\n"		\
+		"	.section __bug_table,\"aw\",@progbits\n"	\
 		"2:	.long	1b\n"					\
 		"	.long	%1\n"					\
 		"	.short	%2\n"					\
@@ -38,7 +38,7 @@
 #define _BUG_OR_WARN(flags)						\
 	asm volatile(							\
 		"1:	.hword	%0\n"					\
-		"	.section __bug_table,\"a\",@progbits\n"		\
+		"	.section __bug_table,\"aw\",@progbits\n"	\
 		"2:	.long	1b\n"					\
 		"	.short	%1\n"					\
 		"	.org	2b + %2\n"				\
diff --git a/arch/mn10300/include/asm/bug.h b/arch/mn10300/include/asm/bug.h
index aa6a38886391..811414fb002d 100644
--- a/arch/mn10300/include/asm/bug.h
+++ b/arch/mn10300/include/asm/bug.h
@@ -21,7 +21,7 @@ do {								\
 	asm volatile(						\
 		"	syscall 15			\n"	\
 		"0:					\n"	\
-		"	.section __bug_table,\"a\"	\n"	\
+		"	.section __bug_table,\"aw\"	\n"	\
 		"	.long 0b,%0,%1			\n"	\
 		"	.previous			\n"	\
 		:						\
diff --git a/arch/parisc/include/asm/bug.h b/arch/parisc/include/asm/bug.h
index d2742273a685..07ea467f22fc 100644
--- a/arch/parisc/include/asm/bug.h
+++ b/arch/parisc/include/asm/bug.h
@@ -27,7 +27,7 @@
 	do {								\
 		asm volatile("\n"					\
 			     "1:\t" PARISC_BUG_BREAK_ASM "\n"		\
-			     "\t.pushsection __bug_table,\"a\"\n"	\
+			     "\t.pushsection __bug_table,\"aw\"\n"	\
 			     "2:\t" ASM_WORD_INSN "1b, %c0\n"		\
 			     "\t.short %c1, %c2\n"			\
 			     "\t.org 2b+%c3\n"				\
@@ -50,7 +50,7 @@
 	do {								\
 		asm volatile("\n"					\
 			     "1:\t" PARISC_BUG_BREAK_ASM "\n"		\
-			     "\t.pushsection __bug_table,\"a\"\n"	\
+			     "\t.pushsection __bug_table,\"aw\"\n"	\
 			     "2:\t" ASM_WORD_INSN "1b, %c0\n"		\
 			     "\t.short %c1, %c2\n"			\
 			     "\t.org 2b+%c3\n"				\
@@ -64,7 +64,7 @@
 	do {								\
 		asm volatile("\n"					\
 			     "1:\t" PARISC_BUG_BREAK_ASM "\n"		\
-			     "\t.pushsection __bug_table,\"a\"\n"	\
+			     "\t.pushsection __bug_table,\"aw\"\n"	\
 			     "2:\t" ASM_WORD_INSN "1b\n"		\
 			     "\t.short %c0\n"				\
 			     "\t.org 2b+%c1\n"				\
diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index 0151af6c2a50..87fcc1948817 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -18,7 +18,7 @@
 #include <asm/asm-offsets.h>
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 .macro EMIT_BUG_ENTRY addr,file,line,flags
-	 .section __bug_table,"a"
+	 .section __bug_table,"aw"
 5001:	 PPC_LONG \addr, 5002f
 	 .short \line, \flags
 	 .org 5001b+BUG_ENTRY_SIZE
@@ -29,7 +29,7 @@
 .endm
 #else
 .macro EMIT_BUG_ENTRY addr,file,line,flags
-	 .section __bug_table,"a"
+	 .section __bug_table,"aw"
 5001:	 PPC_LONG \addr
 	 .short \flags
 	 .org 5001b+BUG_ENTRY_SIZE
@@ -42,14 +42,14 @@
    sizeof(struct bug_entry), respectively */
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 #define _EMIT_BUG_ENTRY				\
-	".section __bug_table,\"a\"\n"		\
+	".section __bug_table,\"aw\"\n"		\
 	"2:\t" PPC_LONG "1b, %0\n"		\
 	"\t.short %1, %2\n"			\
 	".org 2b+%3\n"				\
 	".previous\n"
 #else
 #define _EMIT_BUG_ENTRY				\
-	".section __bug_table,\"a\"\n"		\
+	".section __bug_table,\"aw\"\n"		\
 	"2:\t" PPC_LONG "1b\n"			\
 	"\t.short %2\n"				\
 	".org 2b+%3\n"				\
diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
index 1bbd9dbfe4e0..ce9cc123988b 100644
--- a/arch/s390/include/asm/bug.h
+++ b/arch/s390/include/asm/bug.h
@@ -14,7 +14,7 @@
 		".section .rodata.str,\"aMS\",@progbits,1\n"	\
 		"2:	.asciz	\""__FILE__"\"\n"		\
 		".previous\n"					\
-		".section __bug_table,\"a\"\n"			\
+		".section __bug_table,\"aw\"\n"			\
 		"3:	.long	1b-3b,2b-3b\n"			\
 		"	.short	%0,%1\n"			\
 		"	.org	3b+%2\n"			\
@@ -30,7 +30,7 @@
 	asm volatile(					\
 		"0:	j	0b+2\n"			\
 		"1:\n"					\
-		".section __bug_table,\"a\"\n"		\
+		".section __bug_table,\"aw\"\n"		\
 		"2:	.long	1b-2b\n"		\
 		"	.short	%0\n"			\
 		"	.org	2b+%1\n"		\
diff --git a/arch/sh/include/asm/bug.h b/arch/sh/include/asm/bug.h
index 1b77f068be2b..986c8781d89f 100644
--- a/arch/sh/include/asm/bug.h
+++ b/arch/sh/include/asm/bug.h
@@ -24,14 +24,14 @@
  */
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 #define _EMIT_BUG_ENTRY				\
-	"\t.pushsection __bug_table,\"a\"\n"	\
+	"\t.pushsection __bug_table,\"aw\"\n"	\
 	"2:\t.long 1b, %O1\n"			\
 	"\t.short %O2, %O3\n"			\
 	"\t.org 2b+%O4\n"			\
 	"\t.popsection\n"
 #else
 #define _EMIT_BUG_ENTRY				\
-	"\t.pushsection __bug_table,\"a\"\n"	\
+	"\t.pushsection __bug_table,\"aw\"\n"	\
 	"2:\t.long 1b\n"			\
 	"\t.short %O3\n"			\
 	"\t.org 2b+%O4\n"			\
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 39e702d90cdb..aa6b2023d8f8 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -35,7 +35,7 @@
 #define _BUG_FLAGS(ins, flags)						\
 do {									\
 	asm volatile("1:\t" ins "\n"					\
-		     ".pushsection __bug_table,\"a\"\n"			\
+		     ".pushsection __bug_table,\"aw\"\n"		\
 		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
 		     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"	\
 		     "\t.word %c1"        "\t# bug_entry::line\n"	\
@@ -52,7 +52,7 @@ do {									\
 #define _BUG_FLAGS(ins, flags)						\
 do {									\
 	asm volatile("1:\t" ins "\n"					\
-		     ".pushsection __bug_table,\"a\"\n"			\
+		     ".pushsection __bug_table,\"aw\"\n"		\
 		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
 		     "\t.word %c0"        "\t# bug_entry::flags\n"	\
 		     "\t.org 2b+%c1\n"					\