Re: [PATCH] x86-64: don't leak kernel register values to 32-bitprocesses

[Pavel Machek]

Hi!

> While 32-bit processes can't directly access R8...R15, they can gain
> access to these registers by temporarily switching themselves into
> 64-bit mode. Therefore, registers not preserved anyway by called C
> functions (i.e. R8...R11) must be cleared prior to returning to user
> mode.

How can userspace "temporarily switch itself" to 64bit mode?

Such ability would lead to very interesting behaviour on 32-bit
kernel, I'd say...

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