[PATCH V3 1/7] x86/entry: Introduce __entry_text for entry code written in C

[Lai Jiangshan]

From: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>

Some entry code will be implemented in C files.
Introduce __entry_text to set them in .entry.text section.

The new __entry_text disables instrumentation like noinstr, so
__noinstr_section() is added for noinstr and the new __entry_text.

Note, entry code can not access to %gs before the %gs base is switched
to kernel %gs base, so stack protector can not be used on the C entry
code.  But __entry_text doesn't disable stack protector since some
compilers might not support function level granular attribute to
disable stack protector.  It will be disabled in C file level.

Cc: Borislav Petkov <bp@xxxxxxxxx>
Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
---
 arch/x86/include/asm/idtentry.h | 3 +++
 include/linux/compiler_types.h  | 8 +++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 72184b0b2219..acc4c99f801c 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -13,6 +13,9 @@
 
 #include <asm/irq_stack.h>
 
+/* Entry code written in C. */
+#define __entry_text __noinstr_section(".entry.text")
+
 /**
  * DECLARE_IDTENTRY - Declare functions for simple IDT entry points
  *		      No error code pushed by hardware
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index d08dfcb0ac68..bd9d9d19dc9b 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -225,9 +225,11 @@ struct ftrace_likely_data {
 #endif
 
 /* Section for code which can't be instrumented at all */
-#define noinstr								\
-	noinline notrace __attribute((__section__(".noinstr.text")))	\
-	__no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
+#define __noinstr_section(section)				\
+	noinline notrace __section(section) __no_kcsan		\
+	__no_sanitize_address __no_profile __no_sanitize_coverage
+
+#define noinstr __noinstr_section(".noinstr.text")
 
 #endif /* __KERNEL__ */
 
-- 
2.19.1.6.gb485710b