Re: memcpy is leaking secret data through ZMM vector registers

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On Fri, 19 Apr 2024, H.J. Lu wrote:

> On Fri, Apr 19, 2024 at 7:08 AM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> >
> > I'd like to ask what to do with it? We could use LD_BIND_NOW=1 (or
> > -Wl,-z,now) - it mostly works, but not entirely - the key may still be
> > present on the stack even if we use LD_BIND_NOW=1.
> 
> Since vector registers are saved on stack only during symbol lookup,
> shouldn't disabling lazy binding solve this issue?

It should, but it doesn't fix this problem entirely.

If I set "GLIBC_TUNABLES=glibc.cpu.hwcaps=-AVX512F,-AVX2" "LD_BIND_NOW=1", 
I still get a failure (I don't get the failure if I don't set 
GLIBC_TUNABLES and set only LD_BIND_NOW).

So, even if we use plain SSE, the data somehow end up on the stack.

Mikulas

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