Re: sgx_validate_offset_length bug

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, Oct 05, 2022 at 01:02:39AM +0200, Borys wrote:
> On 10/4/22 23:50, Jarkko Sakkinen wrote:
> > On Mon, Oct 03, 2022 at 07:19:21PM +0200, Borys wrote:
> >> Hi,
> >>
> >> I've stumbled upon "sgx_validate_offset_length" function in
> >> "arch/x86/kernel/cpu/sgx/ioctl.c" (all of this is based on 6.0-rc7
> >> version), which does not entirely do what it claims. "offset" and
> >> "length" parameters are provided by userspace and as such their addition
> >> can overflow, which may result in this function approving malicious
> >> values. Fortunately this does not result in any exploitable bugs at the
> >> moment (or at least I couldn't find any), but this might change if
> >> "sgx_validate_offset_length" is used in a new context or current usages
> >> are changed, so it might be worth fixing anyway. Simple overflow check
> >> `offset + length < offset` should be enough.
> >>
> >> Best regards,
> >>
> >> Borys
> >>
> > 
> > I agree with the bug but not on security issue.
> > 
> > If you can call the ioctl API in the first place, you can already apply
> > the operations in arbitrary locations inside the enclave, i.e. it does
> > not introduce any new capability to the untrusted runtime.
> > 
> > BR, Jarkko
> 
> I meant it could possibly enable some local priv escalation, if other
> code has wrong assumptions. But again, this is purely theoretical,
> current usages fail on invalid values anyway.
> 
> Best regards,
> Borys

Yeah, in all cases it needs to be fixed. Thanks for pointing it out.

BR, Jarkko