Messages in this thread | | | Date | Thu, 25 Mar 2021 08:50:26 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] x86/kprobes: Remove dead code |
| |
On Thu, 25 Mar 2021 07:56:54 +0900 Masami Hiramatsu <mhiramat@kernel.org> wrote:
> On Wed, 24 Mar 2021 17:50:16 +0000 > Colin Ian King <colin.king@canonical.com> 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@gmail.com> > > > --- > > > 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@kernel.org>
| |