Messages in this thread Patch in this message | | | Date | Sun, 24 Sep 2017 13:08:53 -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 Sun, Sep 24, 2017 at 09:02:42PM +0200, Ingo Molnar wrote: > > * Eric Biggers <ebiggers3@gmail.com> wrote: > > > On Sun, Sep 24, 2017 at 12:59:06PM +0200, Ingo Molnar wrote: > > > @@ -328,10 +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); > > > - > > > - /* xcomp_bv must be 0 when using uncompacted format */ > > > - if (!err && fpu->state.xsave.header.xcomp_bv) > > > - err = -EINVAL; > > > + if (!err) > > > + err = validate_xstate_header(&fpu->state.xsave.header); > > > } > > > > > > > Sorry, this is the buggy part. The problem is that this code runs even if XSAVE > > isn't being used --- and in that case the state size is 512 bytes or less, so > > the state doesn't actually include the xstate_header. So > > validate_xstate_header() was reading out of bounds and seeing invalid values. > > > > So I think we need to check use_xsave() here, but it really needs to be in the > > earlier patch which added the check for just ->xcomp_bv ("x86/fpu: Don't let > > userspace set bogus xcomp_bv"), not in this one. > > > > As far the split of patch 2/3 into these 10 patches, it looks fine (though it > > suddenly became a *lot* of patches!). One nit: the subject of this one really > > should say "__fpu__restore_sig()", not "sanitize_restored_xstate()". > > > > I can send a fixed series when I have a chance. > > 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); }
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