On Thu, 25 Mar 2021 07:56:54 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> On Wed, 24 Mar 2021 17:50:16 +0000
> Colin Ian King <colin.king@xxxxxxxxxxxxx> wrote:
>
> > On 24/03/2021 17:36, Muhammad Usama Anjum wrote:
> > > The condition in switch statement `opcode & 0xf0` cannot evaluate to
> > > 0xff. So this case statement will never execute. Remove it.
> > >
> > > Fixes: 6256e668b7 ("x86/kprobes: Use int3 instead of debug trap for single-step")
> > > Signed-off-by: Muhammad Usama Anjum <musamaanjum@xxxxxxxxx>
> > > ---
> > > arch/x86/kernel/kprobes/core.c | 3 ---
> > > 1 file changed, 3 deletions(-)
> > >
> > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> > > index 89d9f26785c7..3b7bcc077020 100644
> > > --- a/arch/x86/kernel/kprobes/core.c
> > > +++ b/arch/x86/kernel/kprobes/core.c
> > > @@ -177,9 +177,6 @@ int can_boost(struct insn *insn, void *addr)
> > > case 0xf0:
> > > /* clear and set flags are boostable */
> > > return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
> > > - case 0xff:
> > > - /* indirect jmp is boostable */
> > > - return X86_MODRM_REG(insn->modrm.bytes[0]) == 4;
> > > default:
> > > /* CS override prefix and call are not boostable */
> > > return (opcode != 0x2e && opcode != 0x9a);
> > >
> >
> > The 0xff case was added with some form of intention to be executed so I
> > suspect removing it is not an appropriate fix.
>
> Right, it must be moved under the case 0xf0. Something like this.
>
> case 0xf0:
> if (opcde == 0xff) {
> /* indirect jmp is boostable */
> return X86_MODRM_REG(insn->modrm.bytes[0]) == 4;
> }
Hmm, wait. I think there is no reason don't use range case.
I think the root cause of this issue is using masked opcode for
switching. Let me clean it up.
Thank you,
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
