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Subject[PATCH -tip v8 05/13] x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline code
Date
From: Josh Poimboeuf <jpoimboe@redhat.com>

Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC
information is generated on the kretprobe_trampoline correctly.

Note that when the CONFIG_FRAME_POINTER=y, since the
kretprobe_trampoline skips updating frame pointer, the stack frame
of the kretprobe_trampoline seems non-standard. So this marks it
is STACK_FRAME_NON_STANDARD() and undefine UNWIND_HINT_FUNC.
Anyway, with the frame pointer, FP unwinder can unwind the stack
frame correctly without that hint.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Andrii Nakryik <andrii@kernel.org>
---
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 | 17 +++++++++++++++--
2 files changed, 20 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 2dccb4347453..74f049b6e77f 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1019,6 +1019,19 @@ int kprobe_int3_handler(struct pt_regs *regs)
}
NOKPROBE_SYMBOL(kprobe_int3_handler);

+#ifdef CONFIG_FRAME_POINTER
+/*
+ * 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 seems to 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(kretprobe_trampoline);
+#undef UNWIND_HINT_FUNC
+#define UNWIND_HINT_FUNC
+#endif
/*
* When a retprobed function returns, this code saves registers and
* calls trampoline_handler() runs, which calls the kretprobe's handler.
@@ -1031,6 +1044,7 @@ 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"
@@ -1041,6 +1055,7 @@ asm(
" popfq\n"
#else
" pushl %esp\n"
+ UNWIND_HINT_FUNC
" pushfl\n"
SAVE_REGS_STRING
" movl %esp, %eax\n"
@@ -1054,8 +1069,6 @@ asm(
".size kretprobe_trampoline, .-kretprobe_trampoline\n"
);
NOKPROBE_SYMBOL(kretprobe_trampoline);
-STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
-

/*
* Called from kretprobe_trampoline
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