Re: [patch V3 11/66] x86/fpu: Sanitize xstateregs_set()

[Borislav Petkov]

On Fri, Jun 18, 2021 at 04:18:34PM +0200, Thomas Gleixner wrote:
> xstateregs_set() operates on a stopped task and tries to copy the provided
> buffer into the task's fpu.state.xsave buffer.
> 
> Any error while copying or invalid state detected after copying results in
> wiping the target task's FPU state completely including supervisor states.
> 
> That's just wrong. The caller supplied invalid data or has a problem with
> unmapped memory, so there is absolutely no justification to corrupt the
> target state.
> 
> Fix this with the following modifications:
> 
>  1) If data has to be copied from userspace, allocate a buffer and copy from
>     user first.
> 
>  2) Use copy_kernel_to_xstate() unconditionally so that header checking
>     works correctly.
> 
>  3) Return on error without corrupting the target state.
> 
> This prevents corrupting states and lets the caller deal with the problem
> it caused in the first place.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/fpu/xstate.h |    4 ---
>  arch/x86/kernel/fpu/regset.c      |   44 +++++++++++++++-----------------------
>  arch/x86/kernel/fpu/xstate.c      |   14 ++++++------
>  3 files changed, 26 insertions(+), 36 deletions(-)

Reviewed-by: Borislav Petkov <bp@xxxxxxx>

Nice!

-- 
Regards/Gruss,
    Boris.

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