Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Feb 12, 2025 at 01:05:09PM +0900, Masami Hiramatsu wrote:
> On Tue, 11 Feb 2025 17:59:41 +0100
> Oleg Nesterov <oleg@redhat.com> wrote:
> 
> > On 02/11, Alexei Starovoitov wrote:
> > >
> > > > > +#define UPROBE_NO_TRAMPOLINE_VADDR ((unsigned long)-1)
> > >
> > > If you respin anyway maybe use ~0UL instead?
> > > In the above and in
> > > uprobe_get_trampoline_vaddr(),
> > > since
> > >
> > > unsigned long trampoline_vaddr = -1;
> > 
> > ... or -1ul in both cases.
> > 
> > I agree, UPROBE_NO_TRAMPOLINE_VADDR has a single user, looks
> > a bit strange...
> 
> I think both this function and uprobe_get_trampoline_vaddr()
> should use the same macro as a token.
> (and ~0UL is a bit more comfortable for me too :) )
> 
> ----
> unsigned long uprobe_get_trampoline_vaddr(void)
> {
> 	struct xol_area *area;
> 	unsigned long trampoline_vaddr = -1;
> ----


sounds good, I'll send new version with change below if there
are no objections

thanks,
jirka


---
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 5a952c5ea66b..015b2a6bac11 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -357,19 +357,23 @@ void *arch_uprobe_trampoline(unsigned long *psize)
 	return &insn;
 }
 
-static unsigned long trampoline_check_ip(void)
+static unsigned long trampoline_check_ip(unsigned long tramp)
 {
-	unsigned long tramp = uprobe_get_trampoline_vaddr();
-
 	return tramp + (uretprobe_syscall_check - uretprobe_trampoline_entry);
 }
 
 SYSCALL_DEFINE0(uretprobe)
 {
 	struct pt_regs *regs = task_pt_regs(current);
-	unsigned long err, ip, sp, r11_cx_ax[3];
+	unsigned long err, ip, sp, r11_cx_ax[3], tramp;
+
+	/* If there's no trampoline, we are called from wrong place. */
+	tramp = uprobe_get_trampoline_vaddr();
+	if (tramp == UPROBE_NO_TRAMPOLINE_VADDR)
+		goto sigill;
 
-	if (regs->ip != trampoline_check_ip())
+	/* Make sure the ip matches the only allowed sys_uretprobe caller. */
+	if (regs->ip != trampoline_check_ip(tramp))
 		goto sigill;
 
 	err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index b1df7d792fa1..a6bec560bdbc 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -39,6 +39,8 @@ struct page;
 
 #define MAX_URETPROBE_DEPTH		64
 
+#define UPROBE_NO_TRAMPOLINE_VADDR	(~0UL)
+
 struct uprobe_consumer {
 	/*
 	 * handler() can return UPROBE_HANDLER_REMOVE to signal the need to
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 2ca797cbe465..e8af2f75b094 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -2160,8 +2160,8 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
  */
 unsigned long uprobe_get_trampoline_vaddr(void)
 {
+	unsigned long trampoline_vaddr = UPROBE_NO_TRAMPOLINE_VADDR;
 	struct xol_area *area;
-	unsigned long trampoline_vaddr = -1;
 
 	/* Pairs with xol_add_vma() smp_store_release() */
 	area = READ_ONCE(current->mm->uprobes_state.xol_area); /* ^^^ */