[PATCH -tip v9 06/14] x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline()

[Masami Hiramatsu]

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Add UNWIND_HINT_FUNC on __kretprobe_trampoline() code so that ORC
information is generated on the __kretprobe_trampoline() correctly.
Also, this uses STACK_FRAME_NON_STANDARD_FP(), CONFIG_FRAME_POINTER-
-specific version of STACK_FRAME_NON_STANDARD().

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Tested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
 Changes in v9:
  - Update changelog and fix comment.
  - Use STACK_FRAME_NON_STANDARD_FP().
 Changes in v4:
  - Apply UNWIND_HINT_FUNC only if CONFIG_FRAME_POINTER=n.
---
 arch/x86/include/asm/unwind_hints.h |    5 +++++
 arch/x86/kernel/kprobes/core.c      |   13 +++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index 8e574c0afef8..8b33674288ea 100644
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -52,6 +52,11 @@
 	UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=8 type=UNWIND_HINT_TYPE_FUNC
 .endm
 
+#else
+
+#define UNWIND_HINT_FUNC \
+	UNWIND_HINT(ORC_REG_SP, 8, UNWIND_HINT_TYPE_FUNC, 0)
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_UNWIND_HINTS_H */
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 79cd23dba5b5..d1436d7463fd 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1025,6 +1025,7 @@ asm(
 	/* We don't bother saving the ss register */
 #ifdef CONFIG_X86_64
 	"	pushq %rsp\n"
+	UNWIND_HINT_FUNC
 	"	pushfq\n"
 	SAVE_REGS_STRING
 	"	movq %rsp, %rdi\n"
@@ -1035,6 +1036,7 @@ asm(
 	"	popfq\n"
 #else
 	"	pushl %esp\n"
+	UNWIND_HINT_FUNC
 	"	pushfl\n"
 	SAVE_REGS_STRING
 	"	movl %esp, %eax\n"
@@ -1048,8 +1050,15 @@ asm(
 	".size __kretprobe_trampoline, .-__kretprobe_trampoline\n"
 );
 NOKPROBE_SYMBOL(__kretprobe_trampoline);
-STACK_FRAME_NON_STANDARD(__kretprobe_trampoline);
-
+/*
+ * __kretprobe_trampoline() skips updating frame pointer. The frame pointer
+ * saved in trampoline_handler() points to the real caller function's
+ * frame pointer. Thus the __kretprobe_trampoline() doesn't have a
+ * standard stack frame with CONFIG_FRAME_POINTER=y.
+ * Let's mark it non-standard function. Anyway, FP unwinder can correctly
+ * unwind without the hint.
+ */
+STACK_FRAME_NON_STANDARD_FP(__kretprobe_trampoline);
 
 /*
  * Called from __kretprobe_trampoline