linux-kernel - Re: [PATCH v3 3/6] ptrace: Order and comment PT

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Message-ID: <YWg+a6PPD5Mpr4c/@hirez.programming.kicks-ass.net>
Date:   Thu, 14 Oct 2021 16:27:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     rjw@...ysocki.net, oleg@...hat.com, mingo@...nel.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, linux-kernel@...r.kernel.org,
        tj@...nel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 3/6] ptrace: Order and comment PT_flags

On Thu, Oct 14, 2021 at 10:31:22AM +0100, Will Deacon wrote:
> On Sat, Oct 09, 2021 at 12:07:57PM +0200, Peter Zijlstra wrote:
> > Add a comment to the PT_flags to indicate their actual value, this
> > makes it easier to see what bits are used and where there might be a
> > possible hole to use.
> > 
> > Notable PT_SEIZED was placed wrong, also PT_EVENT_FLAG() space seems
> > ill defined, as written is seems to be meant to cover the entire
> > PTRACE_O_ range offset by 3 bits, which would then be 3+[0..21],
> > however PT_SEIZED is in the middle of that.
> 
> Why do you think PT_EVENT_FLAG() should cover all the PTRACE_O_* options?
> Just going by the name and current callers, I'd only expect it to cover
> the PTRACE_EVENT_* flags, no?

Because PT_EXITKILL and PT_SUSPEND_SECCOMP are also exposed in that same
mapping.

Ideally we'd change PT_OPT_FLAG_SHIFT to 8 or something and have the
high 24 bits for OPT and then use the low 8 bits for SEIZED and the new
flags.