KPROBE_ENTRY ends up putting code into .fixup

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.

diff -r 30f9dfcdff81 arch/i386/kernel/entry.S
@@ -646,7 +646,7 @@ error_code:

call *%edi
jmp ret_from_exception
CFI_ENDPROC
-.previous
+.popsection

ENTRY(coprocessor_error)
RING0_INT_FRAME
@@ -722,7 +722,7 @@ debug_stack_correct:
call do_debug
jmp ret_from_exception
CFI_ENDPROC
-.previous
+.popsection

/*
* NMI is doubly nasty. It can happen _while_ we're handling
@@ -819,7 +819,7 @@ KPROBE_ENTRY(int3)
call do_int3
jmp ret_from_exception
CFI_ENDPROC
-.previous
+.popsection

ENTRY(overflow)
RING0_INT_FRAME
@@ -884,7 +884,7 @@ KPROBE_ENTRY(general_protection)
CFI_ADJUST_CFA_OFFSET 4
jmp error_code
CFI_ENDPROC
-.previous
+.popsection

ENTRY(alignment_check)
RING0_EC_FRAME

diff -r 30f9dfcdff81 arch/x86_64/kernel/entry.S
@@ -904,7 +904,7 @@ error_kernelspace:
        je   error_swapgs

jmp error_sti
END(error_entry)
- .previous
+ .popsection

       /* Reload gs selector with exception handling */
       /* edi:  new selector */ 

@@ -1024,7 +1024,7 @@ KPROBE_ENTRY(page_fault)
KPROBE_ENTRY(page_fault)
errorentry do_page_fault
END(page_fault)
- .previous
+ .popsection

ENTRY(coprocessor_error)
zeroentry do_coprocessor_error
@@ -1046,7 +1046,7 @@ KPROBE_ENTRY(debug)
paranoidentry do_debug, DEBUG_STACK
paranoidexit
END(debug)
- .previous
+ .popsection

	/* runs on exception stack */	

KPROBE_ENTRY(nmi)
@@ -1061,7 +1061,7 @@ KPROBE_ENTRY(nmi)
CFI_ENDPROC
#endif
END(nmi)
- .previous
+ .popsection

KPROBE_ENTRY(int3)
INTR_FRAME
@@ -1071,7 +1071,7 @@ KPROBE_ENTRY(int3)
jmp paranoid_exit1
CFI_ENDPROC
END(int3)
- .previous
+ .popsection

ENTRY(overflow)
zeroentry do_overflow
@@ -1120,7 +1120,7 @@ KPROBE_ENTRY(general_protection) KPROBE_ENTRY(general_protection)
errorentry do_general_protection
END(general_protection)
- .previous
+ .popsection

ENTRY(alignment_check)
errorentry do_alignment_check

diff -r 30f9dfcdff81 include/linux/linkage.h
@@ -35,7 +35,7 @@

#endif

#define KPROBE_ENTRY(name) \
- .section .kprobes.text, "ax"; \
+ .pushsection .kprobes.text, "ax"; \
ENTRY(name)

#ifndef END

Added thanks.
-Andi