[PATCH v3 06/12] asm-generic: Define CONFIG_HAVE_FUNCTION_DESCRIPTORS

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Replace HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR by a config option
named CONFIG_HAVE_FUNCTION_DESCRIPTORS and use it instead of
'dereference_function_descriptor' macro to know whether an
arch has function descriptors.

To limit churn in one of the following patches, use
an #ifdef/#else construct with empty first part
instead of an #ifndef in asm-generic/sections.h

On powerpc, make sure the config option matches the ABI used
by the compiler with a BUILD_BUG_ON().

And include a helper to check whether an arch has function
descriptors or not : have_function_descriptors()

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/Kconfig                        | 3 +++
 arch/ia64/Kconfig                   | 1 +
 arch/ia64/include/asm/sections.h    | 2 --
 arch/parisc/Kconfig                 | 1 +
 arch/parisc/include/asm/sections.h  | 2 --
 arch/powerpc/Kconfig                | 1 +
 arch/powerpc/include/asm/sections.h | 2 --
 arch/powerpc/kernel/ptrace/ptrace.c | 6 ++++++
 include/asm-generic/sections.h      | 8 +++++++-
 include/linux/kallsyms.h            | 2 +-
 10 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8df1c7102643..6e610a53d832 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -197,6 +197,9 @@ config HAVE_FUNCTION_ERROR_INJECTION
 config HAVE_NMI
 	bool
 
+config HAVE_FUNCTION_DESCRIPTORS
+	bool
+
 config TRACE_IRQFLAGS_SUPPORT
 	bool
 
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 1e33666fa679..97cf02951610 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -34,6 +34,7 @@ config IA64
 	select HAVE_FUNCTION_TRACER
 	select TTY
 	select HAVE_ARCH_TRACEHOOK
+	select HAVE_FUNCTION_DESCRIPTORS
 	select HAVE_VIRT_CPU_ACCOUNTING
 	select HUGETLB_PAGE_SIZE_VARIABLE if HUGETLB_PAGE
 	select VIRT_TO_BUS
diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
index 35f24e52149a..2460d365a057 100644
--- a/arch/ia64/include/asm/sections.h
+++ b/arch/ia64/include/asm/sections.h
@@ -27,8 +27,6 @@ extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_b
 extern char __start_unwind[], __end_unwind[];
 extern char __start_ivt_text[], __end_ivt_text[];
 
-#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
-
 #undef dereference_function_descriptor
 static inline void *dereference_function_descriptor(void *ptr)
 {
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 27a8b49af11f..01d46ca32119 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -65,6 +65,7 @@ config PARISC
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_SOFTIRQ_ON_OWN_STACK if IRQSTACKS
 	select TRACE_IRQFLAGS_SUPPORT
+	select HAVE_FUNCTION_DESCRIPTORS if 64BIT
 
 	help
 	  The PA-RISC microprocessor is designed by Hewlett-Packard and used
diff --git a/arch/parisc/include/asm/sections.h b/arch/parisc/include/asm/sections.h
index bb52aea0cb21..c8092e4d94de 100644
--- a/arch/parisc/include/asm/sections.h
+++ b/arch/parisc/include/asm/sections.h
@@ -9,8 +9,6 @@ extern char __alt_instructions[], __alt_instructions_end[];
 
 #ifdef CONFIG_64BIT
 
-#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
-
 #undef dereference_function_descriptor
 void *dereference_function_descriptor(void *);
 
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index ba5b66189358..0effedba082f 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -208,6 +208,7 @@ config PPC
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS	if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
 	select HAVE_FAST_GUP
 	select HAVE_FTRACE_MCOUNT_RECORD
+	select HAVE_FUNCTION_DESCRIPTORS	if PPC64 && !CPU_LITTLE_ENDIAN
 	select HAVE_FUNCTION_ERROR_INJECTION
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER
diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index abd2e5213197..fb11544d7e6a 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -69,8 +69,6 @@ static inline int overlaps_kernel_text(unsigned long start, unsigned long end)
 
 #ifdef PPC64_ELF_ABI_v1
 
-#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
-
 #undef dereference_function_descriptor
 static inline void *dereference_function_descriptor(void *ptr)
 {
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 7c7093c17c45..740b682caa73 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -446,4 +446,10 @@ void __init pt_regs_check(void)
 	 * real registers.
 	 */
 	BUILD_BUG_ON(PT_DSCR < sizeof(struct user_pt_regs) / sizeof(unsigned long));
+
+#ifdef PPC64_ELF_ABI_v1
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_HAVE_FUNCTION_DESCRIPTORS));
+#else
+	BUILD_BUG_ON(IS_ENABLED(CONFIG_HAVE_FUNCTION_DESCRIPTORS));
+#endif
 }
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index d16302d3eb59..a918388d9bf6 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -59,11 +59,17 @@ extern char __noinstr_text_start[], __noinstr_text_end[];
 extern __visible const void __nosave_begin, __nosave_end;
 
 /* Function descriptor handling (if any).  Override in asm/sections.h */
-#ifndef dereference_function_descriptor
+#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
+#else
 #define dereference_function_descriptor(p) ((void *)(p))
 #define dereference_kernel_function_descriptor(p) ((void *)(p))
 #endif
 
+static inline bool have_function_descriptors(void)
+{
+	return IS_ENABLED(CONFIG_HAVE_FUNCTION_DESCRIPTORS);
+}
+
 /* random extra sections (if any).  Override
  * in asm/sections.h */
 #ifndef arch_is_kernel_text
diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index a1d6fc82d7f0..18799df0c9bf 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -57,7 +57,7 @@ static inline int is_ksym_addr(unsigned long addr)
 
 static inline void *dereference_symbol_descriptor(void *ptr)
 {
-#ifdef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
+#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
 	struct module *mod;
 
 	ptr = dereference_kernel_function_descriptor(ptr);
-- 
2.31.1