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Message-ID: <20210323164801.GE98545@C02TD0UTHF1T.local>
Date: Tue, 23 Mar 2021 16:48:01 +0000
From: Mark Rutland <mark.rutland@....com>
To: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
Cc: broonie@...nel.org, jpoimboe@...hat.com, jthierry@...hat.com,
catalin.marinas@....com, will@...nel.org,
linux-arm-kernel@...ts.infradead.org,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 5/8] arm64: Detect an FTRACE frame and mark a
stack trace unreliable
On Tue, Mar 23, 2021 at 10:26:50AM -0500, Madhavan T. Venkataraman wrote:
> On 3/23/21 9:57 AM, Mark Rutland wrote:
> Thanks for explaining the nesting. It is now clear to me.
No problem!
> So, my next question is - can we define a practical limit for the
> nesting so that any nesting beyond that is fatal? The reason I ask is
> - if there is a max, then we can allocate an array of stack frames out
> of band for the special frames so they are not part of the stack and
> will not likely get corrupted.
I suspect we can't define such a fatal limit without introducing a local
DoS vector on some otherwise legitimate workload, and I fear this will
further complicate the entry/exit logic, so I'd prefer to avoid
introducing a new limit.
What exactly do you mean by a "special frame", and why do those need
additional protection over regular frame records?
> Also, we don't have to do any special detection. If the number of out
> of band frames used is one or more then we have exceptions and the
> stack trace is unreliable.
What is expected to protect against?
Thanks,
Mark.
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