x86/ftrace: Remove OBJECT_FILES_NON_STANDARD usage

The file-wide OBJECT_FILES_NON_STANDARD annotation is used with
CONFIG_FRAME_POINTER to tell objtool to skip the entire file when frame
pointers are enabled.  However that annotation is now deprecated because
it doesn't work with IBT, where objtool runs on vmlinux.o instead of
individual translation units.

Instead, use more fine-grained function-specific annotations:

- The 'save_mcount_regs' macro does funny things with the frame pointer.
  Use STACK_FRAME_NON_STANDARD_FP to tell objtool to ignore the
  functions using it.

- The return_to_handler() "function" isn't actually a callable function.
  Instead of being called, it's returned to.  The real return address
  isn't on the stack, so unwinding is already doomed no matter which
  unwinder is used.  So just remove the STT_FUNC annotation, telling
  objtool to ignore it.  That also removes the implicit
  ANNOTATE_NOENDBR, which now needs to be made explicit.

Fixes the following warning:

  vmlinux.o: warning: objtool: __fentry__+0x16: return with modified stack frame

Fixes: ed53a0d97192 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/b7a7a42fe306aca37826043dac89e113a1acdbac.1654268610.git.jpoimboe@kernel.org

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 03364dc40d8d9195a0115f8bb5245fc08cbf4fb1..4c8b6ae802ac397dca639fae33b8e24538618892 100644 (file)
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -36,10 +36,6 @@ KCSAN_SANITIZE := n
 
 OBJECT_FILES_NON_STANDARD_test_nx.o                    := y
 
-ifdef CONFIG_FRAME_POINTER
-OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o             := y
-endif
-
 # If instrumentation of this dir is enabled, boot hangs during first second.
 # Probably could be more selective here, but note that files related to irqs,
 # boot, dumpstack/stacktrace, etc are either non-interesting or can lead to

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 4ec13608d3c62bd8acae0d897b264cde3eb41e14..dfeb227de5617c6d55ad6ace1f321b7ac87b6a70 100644 (file)
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -175,6 +175,7 @@ SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL)
 
        jmp ftrace_epilogue
 SYM_FUNC_END(ftrace_caller);
+STACK_FRAME_NON_STANDARD_FP(ftrace_caller)
 
 SYM_FUNC_START(ftrace_epilogue)
 /*
@@ -282,6 +283,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
        jmp     ftrace_epilogue
 
 SYM_FUNC_END(ftrace_regs_caller)
+STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)
 
 
 #else /* ! CONFIG_DYNAMIC_FTRACE */
@@ -311,10 +313,14 @@ trace:
        jmp ftrace_stub
 SYM_FUNC_END(__fentry__)
 EXPORT_SYMBOL(__fentry__)
+STACK_FRAME_NON_STANDARD_FP(__fentry__)
+
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-SYM_FUNC_START(return_to_handler)
+SYM_CODE_START(return_to_handler)
+       UNWIND_HINT_EMPTY
+       ANNOTATE_NOENDBR
        subq  $16, %rsp
 
        /* Save the return values */
@@ -339,7 +345,6 @@ SYM_FUNC_START(return_to_handler)
        int3
 .Ldo_rop:
        mov %rdi, (%rsp)
-       UNWIND_HINT_FUNC
        RET
-SYM_FUNC_END(return_to_handler)
+SYM_CODE_END(return_to_handler)
 #endif

diff --git a/include/linux/objtool.h b/include/linux/objtool.h
index 6491fa8fba6d5028eb55cc7c827d162ee7578ef3..15b940ec1eac9d72c0f35c34e52d368fe00a5219 100644 (file)
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -143,6 +143,12 @@ struct unwind_hint {
        .popsection
 .endm
 
+.macro STACK_FRAME_NON_STANDARD_FP func:req
+#ifdef CONFIG_FRAME_POINTER
+       STACK_FRAME_NON_STANDARD \func
+#endif
+.endm
+
 .macro ANNOTATE_NOENDBR
 .Lhere_\@:
        .pushsection .discard.noendbr

diff --git a/tools/include/linux/objtool.h b/tools/include/linux/objtool.h
index 6491fa8fba6d5028eb55cc7c827d162ee7578ef3..15b940ec1eac9d72c0f35c34e52d368fe00a5219 100644 (file)
--- a/tools/include/linux/objtool.h
+++ b/tools/include/linux/objtool.h
@@ -143,6 +143,12 @@ struct unwind_hint {
        .popsection
 .endm
 
+.macro STACK_FRAME_NON_STANDARD_FP func:req
+#ifdef CONFIG_FRAME_POINTER
+       STACK_FRAME_NON_STANDARD \func
+#endif
+.endm
+
 .macro ANNOTATE_NOENDBR
 .Lhere_\@:
        .pushsection .discard.noendbr