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Message-ID: <20191105091723.GC4743@lakrids.cambridge.arm.com>
Date: Tue, 5 Nov 2019 09:17:23 +0000
From: Mark Rutland <mark.rutland@....com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Dave Martin <Dave.Martin@....com>,
Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Marc Zyngier <maz@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 07/17] scs: add support for stack usage debugging
On Mon, Nov 04, 2019 at 01:35:28PM -0800, Sami Tolvanen wrote:
> On Mon, Nov 4, 2019 at 4:40 AM Mark Rutland <mark.rutland@....com> wrote:
> > > +#ifdef CONFIG_DEBUG_STACK_USAGE
> > > +static inline unsigned long scs_used(struct task_struct *tsk)
> > > +{
> > > + unsigned long *p = __scs_base(tsk);
> > > + unsigned long *end = scs_magic(tsk);
> > > + uintptr_t s = (uintptr_t)p;
> >
> > As previously, please use unsigned long for consistency.
>
> Ack.
>
> > > + while (p < end && *p)
> > > + p++;
> >
> > I think this is the only place where we legtimately access the shadow
> > call stack directly.
>
> There's also scs_corrupted, which checks that the end magic is intact.
Ah, true. I missed that.
> > When using SCS and KASAN, are the
> > compiler-generated accesses to the SCS instrumented?
> >
> > If not, it might make sense to make this:
> >
> > while (p < end && READ_ONCE_NOCKECK(*p))
> >
> > ... and poison the allocation from KASAN's PoV, so that we can find
> > unintentional accesses more easily.
>
> Sure, that makes sense. I can poison the allocation for the
> non-vmalloc case, I'll just need to refactor scs_set_magic to happen
> before the poisoning.
Sounds good!
Mark.
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