uprobes/x86: Move UPROBE_FIX_SETF logic from arch_uprobe_post_xol() to default_post_xol_op()

UPROBE_FIX_SETF is only needed to handle "popf" correctly but it is
processed by the generic arch_uprobe_post_xol() code. This doesn't
allows us to make ->fixups private for default_xol_ops.

1 Change default_post_xol_op(UPROBE_FIX_SETF) to set ->saved_tf = T.

   "popf" always reads the flags from stack, it doesn't matter if TF
   was set or not before single-step. Ignoring the naming, this is
   even more logical, "saved_tf" means "owned by application" and we
   do not own this flag after "popf".

2. Change arch_uprobe_post_xol() to save ->saved_tf into the local
   "bool send_sigtrap" before ->post_xol().

3. Change arch_uprobe_post_xol() to ignore UPROBE_FIX_SETF and just
   check ->saved_tf after ->post_xol().

With this patch ->fixups and ->rip_rela_target_address are only used
by default_xol_ops hooks, we are ready to remove them from the common
part of arch_uprobe.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 2efb93f96030..b2bca293fc57 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -441,6 +441,9 @@ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs
                         return -ERESTART;
                 }
         }
+        /* popf; tell the caller to not touch TF */
+        if (auprobe->fixups & UPROBE_FIX_SETF)
+                utask->autask.saved_tf = true;
 
         return 0;
 }
@@ -757,15 +760,15 @@ bool arch_uprobe_xol_was_trapped(struct task_struct *t)
 int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
         struct uprobe_task *utask = current->utask;
+        bool send_sigtrap = utask->autask.saved_tf;
+        int err = 0;
 
         WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
         current->thread.trap_nr = utask->autask.saved_trap_nr;
 
         if (auprobe->ops->post_xol) {
-                int err = auprobe->ops->post_xol(auprobe, regs);
+                err = auprobe->ops->post_xol(auprobe, regs);
                 if (err) {
-                        if (!utask->autask.saved_tf)
-                                regs->flags &= ~X86_EFLAGS_TF;
                         /*
                          * Restore ->ip for restart or post mortem analysis.
                          * ->post_xol() must not return -ERESTART unless this
@@ -773,8 +776,8 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
                          */
                         regs->ip = utask->vaddr;
                         if (err == -ERESTART)
-                                return 0;
-                        return err;
+                                err = 0;
+                        send_sigtrap = false;
                 }
         }
         /*
@@ -782,12 +785,13 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
          * so we can get an extra SIGTRAP if we do not clear TF. We need
          * to examine the opcode to make it right.
          */
-        if (utask->autask.saved_tf)
+        if (send_sigtrap)
                 send_sig(SIGTRAP, current, 0);
-        else if (!(auprobe->fixups & UPROBE_FIX_SETF))
+
+        if (!utask->autask.saved_tf)
                 regs->flags &= ~X86_EFLAGS_TF;
 
-        return 0;
+        return err;
 }
 
 /* callback routine for handling exceptions. */