linux-kernel - Re: [PATCH v2 2/2] x86/kprobes: Prohibit probing on compiler generated CFI checking code

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Date:   Thu, 27 Jul 2023 09:40:07 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Petr Pavlu <petr.pavlu@...e.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, samitolvanen@...gle.com, x86@...nel.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] x86/kprobes: Prohibit probing on compiler
 generated CFI checking code

On Wed, 26 Jul 2023 11:29:17 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Jul 26, 2023 at 12:23:17PM +0900, Masami Hiramatsu wrote:
> > On Tue, 11 Jul 2023 10:50:58 +0900
> > "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> > 
> > > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > > 
> > > Prohibit probing on the compiler generated CFI typeid checking code
> > > because it is used for decoding typeid when CFI error happens.
> > > 
> > > The compiler generates the following instruction sequence for indirect
> > > call checks on x86;
> > > 
> > >    movl    -<id>, %r10d       ; 6 bytes
> > >    addl    -4(%reg), %r10d    ; 4 bytes
> > >    je      .Ltmp1             ; 2 bytes
> > >    ud2                        ; <- regs->ip
> > > 
> > > And handle_cfi_failure() decodes these instructions (movl and addl)
> > > for the typeid and the target address. Thus if we put a kprobe on
> > > those instructions, the decode will fail and report a wrong typeid
> > > and target address.
> > > 
> > > 
> > 
> > Hi Peter,
> > 
> > Can I pick this to probes/fixes branch ?
> 
> I'll stick them in tip/x86/core, that ok?

Yes, since it is for CFI change. 

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>