[RFC PATCH v2 1/4] uretprobes/x86: hijack return address

[Anton Arapov <anton@redhat.com>]

Function to hijack the return address, replace it with a "trampoline"
and function to predict the stack pointer address value at return.

v2:
  remove ->doomed flag, kill task immediately

Signed-off-by: Anton Arapov <anton@redhat.com>
---
 arch/x86/include/asm/uprobes.h |  1 +
 arch/x86/kernel/uprobes.c      | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 8ff8be7..c353555 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -55,4 +55,5 @@ extern int  arch_uprobe_post_xol(struct arch_uprobe *aup, struct pt_regs *regs);
 extern bool arch_uprobe_xol_was_trapped(struct task_struct *tsk);
 extern int  arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data);
 extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs *regs);
+extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long rp_trampoline_vaddr, struct pt_regs *regs);
 #endif	/* _ASM_UPROBES_H */
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0ba4cfb..85e2153 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -697,3 +697,32 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 		send_sig(SIGTRAP, current, 0);
 	return ret;
 }
+
+extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long
+		rp_trampoline_vaddr, struct pt_regs *regs)
+{
+	int rasize, ncopied;
+	unsigned long orig_ret_vaddr = 0; /* clear high bits for 32-bit apps */
+
+	rasize = is_ia32_task() ? 4 : 8;
+	ncopied = copy_from_user(&orig_ret_vaddr, (void __user *)regs->sp, rasize);
+	if (unlikely(ncopied))
+		return 0;
+
+	/* check whether address has been already hijacked */
+	if (orig_ret_vaddr == rp_trampoline_vaddr)
+		return orig_ret_vaddr;
+
+	ncopied = copy_to_user((void __user *)regs->sp, &rp_trampoline_vaddr, rasize);
+	if (unlikely(ncopied)) {
+		if (ncopied != rasize) {
+			printk(KERN_ERR "uretprobe: return address clobbered: "
+					"pid=%d, %%sp=%#lx, %%ip=%#lx\n",
+					current->pid, regs->sp, regs->ip);
+			/* kill task immediately */
+			send_sig(SIGSEGV, current, 0);
+		}
+	}
+
+	return orig_ret_vaddr;
+}
-- 
1.8.0.2