[PATCH 07/10] uprobes/x86: Introduce arch_uretprobe_is_alive()

[Oleg Nesterov]

Add the x86-specific arch_uretprobe_is_alive() helper and define its
"weak" version for other architectures.

It returns true if the stack frame mangled by prepare_uretprobe() is
still on stack. So if it returns false, we know that the probed func
has already returned.

TODO: this assumes that the probed app can't use multiple stacks (say
sigaltstack). We will try to improve this logic later.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 arch/x86/include/asm/uprobes.h |    1 +
 arch/x86/kernel/uprobes.c      |    6 ++++++
 include/linux/uprobes.h        |    1 +
 kernel/events/uprobes.c        |    4 ++++
 4 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index f011fd0..60777f3 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -57,6 +57,7 @@ struct arch_uprobe {
 };
 
 struct arch_uretprobe {
+	unsigned long	sp;
 };
 
 struct arch_uprobe_task {
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0270315..868dc47 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -907,6 +907,7 @@ arch_uretprobe_hijack_return_addr(struct arch_uretprobe *auret,
 	int rasize = sizeof_long(), nleft;
 	unsigned long orig_ret_vaddr = 0; /* clear high bits for 32-bit apps */
 
+	auret->sp = regs->sp;
 	if (copy_from_user(&orig_ret_vaddr, (void __user *)regs->sp, rasize))
 		return -1;
 
@@ -927,3 +928,8 @@ arch_uretprobe_hijack_return_addr(struct arch_uretprobe *auret,
 
 	return -1;
 }
+
+bool arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct pt_regs *regs)
+{
+	return regs->sp <= auret->sp;
+}
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 144571b..1ed7502 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -129,6 +129,7 @@ extern int  arch_uprobe_exception_notify(struct notifier_block *self, unsigned l
 extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs *regs);
 extern unsigned long arch_uretprobe_hijack_return_addr(struct arch_uretprobe *auret,
 					unsigned long trampoline_vaddr, struct pt_regs *regs);
+extern bool arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct pt_regs *regs);
 extern bool arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
 extern void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
 					 void *src, unsigned long len);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 19af44a..0f68ea2 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1820,6 +1820,10 @@ bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs)
 	return false;
 }
 
+bool __weak arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct pt_regs *regs)
+{
+	return true;
+}
 /*
  * Run handler and ask thread to singlestep.
  * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
-- 
1.5.5.1

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