[PATCH -tip v8 10/13] x86/kprobes: Push a fake return address at kretprobe_trampoline

Masami Hiramatsu
2021-06-18T07:06:56Z

This changes x86/kretprobe stack frame on kretprobe_trampoline
a bit, which now push the kretprobe_trampoline as a fake return
address at the bottom of the stack frame. With this fix, the ORC
unwinder will see the kretprobe_trampoline as a return address.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Andrii Nakryik <andrii@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/kernel/kprobes/core.c | 31 ++++++++++++++++++++++---------
1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 74f049b6e77f..4d040aaf969b 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1041,28 +1041,31 @@ asm(
".global kretprobe_trampoline\n"
".type kretprobe_trampoline, @function\n"
"kretprobe_trampoline:\n"
- /* We don't bother saving the ss register */
#ifdef CONFIG_X86_64
- " pushq %rsp\n"
+ /* Push fake return address to tell the unwinder it's a kretprobe */
+ " pushq $kretprobe_trampoline\n"
UNWIND_HINT_FUNC
+ /* Save the sp-8, this will be fixed later */
+ " pushq %rsp\n"
" pushfq\n"
SAVE_REGS_STRING
" movq %rsp, %rdi\n"
" call trampoline_handler\n"
- /* Replace saved sp with true return address. */
- " movq %rax, 19*8(%rsp)\n"
RESTORE_REGS_STRING
+ " addq $8, %rsp\n"
" popfq\n"
#else
- " pushl %esp\n"
+ /* Push fake return address to tell the unwinder it's a kretprobe */
+ " pushl $kretprobe_trampoline\n"
UNWIND_HINT_FUNC
+ /* Save the sp-4, this will be fixed later */
+ " pushl %esp\n"
" pushfl\n"
SAVE_REGS_STRING
" movl %esp, %eax\n"
" call trampoline_handler\n"
- /* Replace saved sp with true return address. */
- " movl %eax, 15*4(%esp)\n"
RESTORE_REGS_STRING
+ " addl $4, %esp\n"
" popfl\n"
#endif
" ret\n"
@@ -1073,8 +1076,10 @@ NOKPROBE_SYMBOL(kretprobe_trampoline);
/*
* Called from kretprobe_trampoline
*/
-__used __visible void *trampoline_handler(struct pt_regs *regs)
+__used __visible void trampoline_handler(struct pt_regs *regs)
{
+ unsigned long *frame_pointer;
+
/* fixup registers */
regs->cs = __KERNEL_CS;
#ifdef CONFIG_X86_32
@@ -1082,8 +1087,16 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
#endif
regs->ip = (unsigned long)&kretprobe_trampoline;
regs->orig_ax = ~0UL;
+ regs->sp += sizeof(long);
+ frame_pointer = ((unsigned long *)&regs->sp) + 1;

- return (void *)kretprobe_trampoline_handler(regs, &regs->sp);
+ /* Replace fake return address with real one. */
+ *frame_pointer = kretprobe_trampoline_handler(regs, frame_pointer);
+ /*
+ * Move flags to sp so that kretprobe_trapmoline can return
+ * right after popf.
+ */
+ regs->sp = regs->flags;
}
NOKPROBE_SYMBOL(trampoline_handler);