[RFC PATCH 1/6] uprobes/x86: Emulate unconditional rip-relative jmp's

[Oleg Nesterov <oleg@redhat.com>]

0xeb and 0xe9. Anything else?

TODO: move ->fixup into the union along with rip_rela_target_address.

Reported-by: Jonathan Lebon <jlebon@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/include/asm/uprobes.h |    8 +++++++-
 arch/x86/kernel/uprobes.c      |   40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 9f8210b..cca62c5 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -44,9 +44,15 @@ struct arch_uprobe {
 	u16				fixups;
 	const struct uprobe_xol_ops	*ops;
 
+	union {
 #ifdef CONFIG_X86_64
-	unsigned long			rip_rela_target_address;
+		unsigned long			rip_rela_target_address;
 #endif
+		struct {
+			s32	disp;
+			u8	ilen;
+		}				ttt;
+	};
 };
 
 struct arch_uprobe_task {
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 1ea7e1a..32ab147 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -466,6 +466,42 @@ static struct uprobe_xol_ops default_xol_ops = {
 	.post_xol = default_post_xol_op,
 };
 
+static bool ttt_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+	regs->ip += auprobe->ttt.ilen + auprobe->ttt.disp;
+	return true;
+}
+
+static struct uprobe_xol_ops ttt_xol_ops = {
+	.emulate  = ttt_emulate_op,
+};
+
+static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
+{
+
+	switch (OPCODE1(insn)) {
+	case 0xeb:	/* jmp 8 */
+	case 0xe9:	/* jmp 32 */
+		break;
+	default:
+		return -ENOSYS;
+	}
+
+	/* has the side-effect of processing the entire instruction */
+	insn_get_length(insn);
+	if (WARN_ON_ONCE(!insn_complete(insn)))
+		return -ENOEXEC;
+
+	auprobe->ttt.ilen = insn->length;
+	auprobe->ttt.disp = insn->moffset1.value;
+	/* so far we assume that it fits into ->moffset1 */
+	if (WARN_ON_ONCE(insn->moffset2.nbytes))
+		return -ENOEXEC;
+
+	auprobe->ops = &ttt_xol_ops;
+	return 0;
+}
+
 /**
  * arch_uprobe_analyze_insn - instruction analysis including validity and fixups.
  * @mm: the probed address space.
@@ -483,6 +519,10 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	if (ret)
 		return ret;
 
+	ret = ttt_setup_xol_ops(auprobe, &insn);
+	if (ret == 0 || ret != ENOSYS)
+		return ret;
+
 	/*
 	 * Figure out which fixups arch_uprobe_post_xol() will need to perform,
 	 * and annotate arch_uprobe->fixups accordingly. To start with, ->fixups
-- 
1.5.5.1