Messages in this thread | | | Date | Mon, 25 Sep 2017 00:20:10 -0700 | From | Eric Biggers <> | Subject | Re: [PATCH 03/10] x86/fpu: Use validate_xstate_header() to validate the xstate_header in sanitize_restored_xstate() |
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On Mon, Sep 25, 2017 at 08:14:45AM +0200, Ingo Molnar wrote: > > > > > > Could you please just send the delta patch against the whole tree to fix the bug? > > > I'll worry about the patch dependencies and back-merge it to the proper place. > > > > > > > The following diff against tip/master fixes the bug. Note: we *could* check > > 'use_xsave()' instead of 'state_size > offsetof(struct xregs_state, header)', > > but that might be confusing in the case where we couldn't find the xstate > > information in the memory layout and only copy the fxregs_state, since then we'd > > actually be validating the xsave_header which was already there, which shouldn't > > ever fail. > > > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > > index afe54247cf27..fb639e70048f 100644 > > --- a/arch/x86/kernel/fpu/signal.c > > +++ b/arch/x86/kernel/fpu/signal.c > > @@ -331,7 +331,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > > err = copy_user_to_xstate(&fpu->state.xsave, buf_fx); > > } else { > > err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size); > > - if (!err) > > + > > + if (!err && state_size > offsetof(struct xregs_state, header)) > > err = validate_xstate_header(&fpu->state.xsave.header); > > } > > I.e. a better check would be to check that the whole header can be accessed: > > state_size >= offsetof(struct xregs_state, header) + sizeof(struct xstate_header) > > Not that there should ever be a 'state_size' that points inside the header - so in > the end I back-merged your original (and tested ...) version. >
Well, actually we'd need to validate the header if userspace overwrote any part of it.
But more importantly, I think the state_size check needs to go into the first patch (the one that's Cc'ed to stable as it fixes the real bug), since ->xcomp_bv is part of the xstate_header. So *before* we switch to validate_xstate_header() in this patch, the code should already be:
if (using_compacted_format()) { err = copy_user_to_xstate(&fpu->state.xsave, buf_fx); } else { err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
/* xcomp_bv must be 0 when using uncompacted format */ if (!err && state_size > offsetof(struct xregs_state, header) && fpu->state.xsave.header.xcomp_bv) err = -EINVAL; }
Also can you please fix the commit title and message of this patch? It should say "__fpu__restore_sig()", not "sanitize_restored_xstate()".
Thanks,
Eric
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