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Date:   Mon, 29 Oct 2018 23:55:06 -0700 (PDT)
From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
To:     Linux-Kernel <linux-kernel@vger.kernel.org>
Cc:     <mingo@redhat.com>, <konrad.wilk@oracle.com>, <dwmw@amazon.co.uk>,
        <tglx@linutronix.de>,
        Srinivas REDDY Eeda <srinivas.eeda@oracle.com>, <bp@suse.de>,
        <peterz@infradead.org>, <hpa@zytor.com>
Subject: [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in retpoline
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Sender: linux-kernel-owner@vger.kernel.org
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Since CONFIG_RETPOLINE hard depends on compiler support now, so
replacing indirect-jump check with the range check is safe in that case.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 arch/x86/kernel/kprobes/opt.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 40b16b2..1136b29 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -203,6 +203,7 @@ static int copy_optimized_instructions(u8 *dest, u8 *sr=
c, u8 *real)
 =09return len;
 }
=20
+#ifndef CONFIG_RETPOLINE
 /* Check whether insn is indirect jump */
 static int __insn_is_indirect_jump(struct insn *insn)
 {
@@ -210,6 +211,7 @@ static int __insn_is_indirect_jump(struct insn *insn)
 =09=09(X86_MODRM_REG(insn->modrm.value) & 6) =3D=3D 4) || /* Jump */
 =09=09insn->opcode.bytes[0] =3D=3D 0xea);=09/* Segment based jump */
 }
+#endif
=20
 /* Check whether insn jumps into specified address range */
 static int insn_jump_into_range(struct insn *insn, unsigned long start, in=
t len)
@@ -240,20 +242,16 @@ static int insn_jump_into_range(struct insn *insn, un=
signed long start, int len)
=20
 static int insn_is_indirect_jump(struct insn *insn)
 {
-=09int ret =3D __insn_is_indirect_jump(insn);
+=09int ret;
=20
 #ifdef CONFIG_RETPOLINE
-=09/*
-=09 * Jump to x86_indirect_thunk_* is treated as an indirect jump.
-=09 * Note that even with CONFIG_RETPOLINE=3Dy, the kernel compiled with
-=09 * older gcc may use indirect jump. So we add this check instead of
-=09 * replace indirect-jump check.
-=09 */
-=09if (!ret)
+=09/* Jump to x86_indirect_thunk_* is treated as an indirect jump. */
 =09=09ret =3D insn_jump_into_range(insn,
 =09=09=09=09(unsigned long)__indirect_thunk_start,
 =09=09=09=09(unsigned long)__indirect_thunk_end -
 =09=09=09=09(unsigned long)__indirect_thunk_start);
+#else
+=09=09ret =3D __insn_is_indirect_jump(insn);
 #endif
 =09return ret;
 }
--=20
1.8.3.1