uprobes/x86: Kill adjust_ret_addr(), simplify UPROBE_FIX_CALL logic

The only insn which could have both UPROBE_FIX_IP and UPROBE_FIX_CALL
was 0xe8 "call relative", and now it is handled by branch_xol_ops.

So we can change default_post_xol_op(UPROBE_FIX_CALL) to simply push
the address of next insn == utask->vaddr + insn.length, just we need
to record insn.length into the new auprobe->def.ilen member.

Note: if/when we teach branch_xol_ops to support jcxz/loopz we can
remove the "correction" logic, UPROBE_FIX_IP can use the same address.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

2 files changed, 4 insertions, 21 deletions

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 9ce25ce04fee..a040d493a4f9 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -54,6 +54,7 @@ struct arch_uprobe {
                         long    riprel_target;
 #endif
                         u8      fixups;
+                        u8      ilen;
                 }                       def;
         };
 };
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index df75913acfc0..5bcce852628a 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -418,24 +418,6 @@ static int push_ret_address(struct pt_regs *regs, unsigned long ip)
         return 0;
 }
 
-/*
- * Adjust the return address pushed by a call insn executed out of line.
- */
-static int adjust_ret_addr(unsigned long sp, long correction)
-{
-        int rasize = sizeof_long();
-        long ra;
-
-        if (copy_from_user(&ra, (void __user *)sp, rasize))
-                return -EFAULT;
-
-        ra += correction;
-        if (copy_to_user((void __user *)sp, &ra, rasize))
-                return -EFAULT;
-
-        return 0;
-}
-
 static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {
         struct uprobe_task *utask = current->utask;
@@ -446,10 +428,9 @@ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs
                 regs->ip += correction;
 
         if (auprobe->def.fixups & UPROBE_FIX_CALL) {
-                if (adjust_ret_addr(regs->sp, correction)) {
-                        regs->sp += sizeof_long();
+                regs->sp += sizeof_long();
+                if (push_ret_address(regs, utask->vaddr + auprobe->def.ilen))
                         return -ERESTART;
-                }
         }
         /* popf; tell the caller to not touch TF */
         if (auprobe->def.fixups & UPROBE_FIX_SETF)
@@ -687,6 +668,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
                 handle_riprel_insn(auprobe, &insn);
         }
 
+        auprobe->def.ilen = insn.length;
         if (fix_ip)
                 auprobe->def.fixups |= UPROBE_FIX_IP;
         if (fix_call)