[PATCH] x86: error_code is not safe for kprobes

This patch moves the entry.S:error_entry to .kprobes.text section,
since code marked unsafe for kprobes jumps directly to entry.S::error_entry,
that must be marked unsafe as well.
This patch also moves all the ".previous.text" asm directives to ".previous"
for kprobes section.

AK: Following a similar i386 patch from Chuck Ebbert
AK: Also merged Jeremy's fix in.

+From: Jeremy Fitzhardinge <jeremy@goop.org>

KPROBE_ENTRY does a .section .kprobes.text, and expects its users to
do a .previous at the end of the function.

Unfortunately, if any code within the function switches sections, for
example .fixup, then the .previous ends up putting all subsequent code
into .fixup.  Worse, any subsequent .fixup code gets intermingled with
the code its supposed to be fixing (which is also in .fixup).  It's
surprising this didn't cause more havok.

The fix is to use .pushsection/.popsection, so this stuff nests
properly.  A further cleanup would be to get rid of all
.section/.previous pairs, since they're inherently fragile.

+From: Chuck Ebbert <76306.1226@compuserve.com>

Because code marked unsafe for kprobes jumps directly to
entry.S::error_code, that must be marked unsafe as well.
The easiest way to do that is to move the page fault entry
point to just before error_code and let it inherit the same
section.

Also moved all the ".previous" asm directives for kprobes
sections to column 1 and removed ".text" from them.

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andi Kleen <ak@suse.de>

arch/i386/kernel/entry.S

@@ -591,11 +591,9 @@ ENTRY(name)				\
 /* The include is where all of the SMP etc. interrupts come from */
 #include "entry_arch.h"
 
-ENTRY(divide_error)
-	RING0_INT_FRAME
-	pushl $0			# no error code
-	CFI_ADJUST_CFA_OFFSET 4
-	pushl $do_divide_error
+KPROBE_ENTRY(page_fault)
+	RING0_EC_FRAME
+	pushl $do_page_fault
 	CFI_ADJUST_CFA_OFFSET 4
 	ALIGN
 error_code:
@@ -645,6 +643,7 @@ error_code:
 	call *%edi
 	jmp ret_from_exception
 	CFI_ENDPROC
+KPROBE_END(page_fault)
 
 ENTRY(coprocessor_error)
 	RING0_INT_FRAME
@@ -720,7 +719,8 @@ debug_stack_correct:
 	call do_debug
 	jmp ret_from_exception
 	CFI_ENDPROC
-	.previous .text
+KPROBE_END(debug)
+
 /*
  * NMI is doubly nasty. It can happen _while_ we're handling
  * a debug fault, and the debug fault hasn't yet been able to
@@ -816,7 +816,7 @@ KPROBE_ENTRY(int3)
 	call do_int3
 	jmp ret_from_exception
 	CFI_ENDPROC
-	.previous .text
+KPROBE_END(int3)
 
 ENTRY(overflow)
 	RING0_INT_FRAME
@@ -881,7 +881,7 @@ KPROBE_ENTRY(general_protection)
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp error_code
 	CFI_ENDPROC
-	.previous .text
+KPROBE_END(general_protection)
 
 ENTRY(alignment_check)
 	RING0_EC_FRAME
@@ -890,13 +890,14 @@ ENTRY(alignment_check)
 	jmp error_code
 	CFI_ENDPROC
 
-KPROBE_ENTRY(page_fault)
-	RING0_EC_FRAME
-	pushl $do_page_fault
+ENTRY(divide_error)
+	RING0_INT_FRAME
+	pushl $0			# no error code
+	CFI_ADJUST_CFA_OFFSET 4
+	pushl $do_divide_error
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp error_code
 	CFI_ENDPROC
-	.previous .text
 
 #ifdef CONFIG_X86_MCE
 ENTRY(machine_check)

arch/x86_64/kernel/entry.S

@@ -819,7 +819,7 @@ paranoid_schedule\trace:
  * Exception entry point. This expects an error code/orig_rax on the stack
  * and the exception handler in %rax.	
  */ 		  				
-ENTRY(error_entry)
+KPROBE_ENTRY(error_entry)
 	_frame RDI
 	/* rdi slot contains rax, oldrax contains error code */
 	cld	
@@ -903,7 +903,7 @@ error_kernelspace:
 	cmpq $gs_change,RIP(%rsp)
         je   error_swapgs
 	jmp  error_sti
-END(error_entry)
+KPROBE_END(error_entry)
 
        /* Reload gs selector with exception handling */
        /* edi:  new selector */ 
@@ -1025,8 +1025,7 @@ ENDPROC(execve)
 
 KPROBE_ENTRY(page_fault)
 	errorentry do_page_fault
-END(page_fault)
-	.previous .text
+KPROBE_END(page_fault)
 
 ENTRY(coprocessor_error)
 	zeroentry do_coprocessor_error
@@ -1047,8 +1046,7 @@ KPROBE_ENTRY(debug)
 	CFI_ADJUST_CFA_OFFSET 8		
 	paranoidentry do_debug, DEBUG_STACK
 	paranoidexit
-END(debug)
-	.previous .text
+KPROBE_END(debug)
 
 	/* runs on exception stack */	
 KPROBE_ENTRY(nmi)
@@ -1062,8 +1060,7 @@ KPROBE_ENTRY(nmi)
 	jmp paranoid_exit1
  	CFI_ENDPROC
 #endif
-END(nmi)
-	.previous .text
+KPROBE_END(nmi)
 
 KPROBE_ENTRY(int3)
  	INTR_FRAME
@@ -1072,8 +1069,7 @@ KPROBE_ENTRY(int3)
  	paranoidentry do_int3, DEBUG_STACK
  	jmp paranoid_exit1
  	CFI_ENDPROC
-END(int3)
-	.previous .text
+KPROBE_END(int3)
 
 ENTRY(overflow)
 	zeroentry do_overflow
@@ -1121,8 +1117,7 @@ END(stack_segment)
 
 KPROBE_ENTRY(general_protection)
 	errorentry do_general_protection
-END(general_protection)
-	.previous .text
+KPROBE_END(general_protection)
 
 ENTRY(alignment_check)
 	errorentry do_alignment_check

include/linux/linkage.h

@@ -35,9 +35,13 @@
 #endif
 
 #define KPROBE_ENTRY(name) \
-  .section .kprobes.text, "ax"; \
+  .pushsection .kprobes.text, "ax"; \
   ENTRY(name)
 
+#define KPROBE_END(name) \
+  END(name);		 \
+  .popsection
+
 #ifndef END
 #define END(name) \
   .size name, .-name