Re: Potential information leak in save_xstate_epilog()

[Thomas Gleixner]

On Fri, Nov 26 2021 at 12:06, Alexander Potapenko wrote:
> Hi Chang, Thomas, Borislav,
>
> "x86/fpu/signal: Prepare for variable sigframe length" has presumably
> introduced an information leak to the userspace.
>
> According to https://elixir.bootlin.com/linux/v5.16-rc2/source/arch/x86/kernel/fpu/signal.c#L126,
> save_sw_bytes() only initializes the first 20 bytes of sw_bytes, but
> then the whole struct is copied to the userspace.

Yes, that clearly lacks a memset(0).

Thanks,

        tglx