Hi Eric, On Thu, Aug 25, 2022 at 11:15:58PM +0000, Eric Biggers wrote: > I'm wondering if people are aware of this issue, and whether anyone has any > thoughts on whether/where the kernel should be setting these new CPU flags. > There don't appear to have been any prior discussions about this. (Thanks to Maybe it should be set unconditionally now, until we figure out how to make it more granular. 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? Jason
