From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: x86@kernel.org, linux-arm-kernel@lists.infradead.org,
linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
Adam Langley <agl@google.com>, Ard Biesheuvel <ardb@kernel.org>
Subject: Re: Should Linux set the new constant-time mode CPU flags?
Date: Mon, 29 Aug 2022 15:05:59 -0400 [thread overview]
Message-ID: <Yw0OF89auWTh12Xd@zx2c4.com> (raw)
In-Reply-To: <Ywzr2d52ixYXUDWR@zx2c4.com>
On Mon, Aug 29, 2022 at 12:39:53PM -0400, Jason A. Donenfeld wrote:
> In terms of granularity, I saw other folks suggesting making it per-task
> (so, presumably, a prctl() knob), and others mentioning doing it just
> for kernel crypto. For the latter, I guess the crypto API could set it
> inside of its abstractions, and the various lib/crypto APIs could set it
> at invocation time. I wonder, though, what's the cost of
> enabling/disabling it? Would we in fact need a kind of lazy-deferred
> disabling, like we have with kernel_fpu_end()? I also wonder what
> crypto-adjacent code might wind up being missed if we're going function
> by function. Like, obviously we'd set this for crypto_memneq, but what
> about potential unprotected `==` of ID numbers that could leak some info
> in various protocols? What other subtle nearby code should we be
> thinking about, that relies on constant time logic but isn't neatly
> folded inside a crypto_do_something() function?
Another random note on this: I would hope that setting that MSR
represents a speculation barrier or general instruction stream barrier,
so that you can't do something naughty with the scheduler to toggle it
rapidly and measure crypto timings somehow.
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next prev parent reply other threads:[~2022-08-29 19:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 23:15 Should Linux set the new constant-time mode CPU flags? Eric Biggers
2022-08-26 7:23 ` Peter Zijlstra
2022-08-26 8:45 ` Arnd Bergmann
2022-09-15 17:18 ` Catalin Marinas
2022-08-26 15:40 ` Jeffrey Walton
2022-08-29 16:39 ` Jason A. Donenfeld
2022-08-29 18:08 ` Eric Biggers
2022-08-29 19:09 ` Jason A. Donenfeld
2022-08-29 19:05 ` Jason A. Donenfeld [this message]
2022-08-30 14:25 ` Dave Hansen
2022-09-01 11:00 ` Peter Zijlstra
2022-10-25 5:06 ` Eric Biggers
2022-09-15 17:52 ` Catalin Marinas
2022-10-26 17:01 ` Ard Biesheuvel
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