On Tue, Jun 23, 2026 at 9:25 AM Oleg Nesterov [off-list ref] wrote:

On 06/23, Peter Zijlstra wrote:

quoted

On Tue, Jun 23, 2026 at 02:52:32PM +0200, Oleg Nesterov wrote:

quoted

On 06/22, David Windsor wrote:

quoted

--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c

@@ -1246,8 +1246,12 @@ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs
          long correction = utask->vaddr - utask->xol_vaddr;
          regs->ip += correction;
  } else if (auprobe->defparam.fixups & UPROBE_FIX_CALL) {
+         unsigned long retaddr = utask->vaddr + auprobe->defparam.ilen;
+
          regs->sp += sizeof_long(regs); /* Pop incorrect return address */
-         if (emulate_push_stack(regs, utask->vaddr + auprobe->defparam.ilen))
+         if (emulate_push_stack(regs, retaddr))
+                 return -ERESTART;
+         if (shstk_update_last_frame(retaddr))
                  return -ERESTART;

Well, if shstk_update_last_frame() fails after emulate_push_stack(), we should
probably return another error, so that the caller handle_singlestep() will kill
this task?

Makes sense, the other user has a force_sig(SIGSEGV) on failure.

Offtopic question... both shstk_update_last_frame() and shstk_push() are only
used by arch/x86/kernel/uprobes.c. But they are not symmetric in that
shstk_update_last_frame() returns 0 if !features_enabled(ARCH_SHSTK_SHSTK),
while shstk_push() returns -ENOTSUPP in this case.

That is why the users can't just do "if (shstk_push(xxx)) ...". This is really
minor, but perhaps it makes sense to change shstk_push() to return 0 in this
case too? I don't think -ENOTSUPP is actually useful...

Agreed, will send a follow-up patch changing shstk_push() to return 0
rather than -ENOTSUPP.

I'll send v2 shortly with the additional call to force_sig(SIGSEGV) to
balance out the callers.

Oleg.