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    SubjectRe: [patch V2 09/52] x86/fpu: Reject invalid MXCSR values in copy_kernel_to_xstate()
    Date
    On Wed, Jun 16 2021 at 17:02, Borislav Petkov wrote:
    > On Mon, Jun 14, 2021 at 05:44:17PM +0200, Thomas Gleixner wrote:
    >> Instead of masking out reserved bits, check them and reject the provided
    >> state as invalid if not zero.
    >>
    >> Suggested-by: Andy Lutomirski <luto@kernel.org>
    >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    >> ---
    >> V2: New patch
    >> ---
    >> arch/x86/kernel/fpu/xstate.c | 11 ++++++++---
    >> 1 file changed, 8 insertions(+), 3 deletions(-)
    >>
    >> --- a/arch/x86/kernel/fpu/xstate.c
    >> +++ b/arch/x86/kernel/fpu/xstate.c
    >> @@ -1166,6 +1166,14 @@ int copy_kernel_to_xstate(struct xregs_s
    >> if (validate_user_xstate_header(&hdr))
    >> return -EINVAL;
    >>
    >> + if (xfeatures_mxcsr_quirk(hdr.xfeatures)) {
    >
    > Since we're cleaning up this FPU stinking pile - that function needs to
    > have a verb in the name, something like:
    >
    > if (xfeatures_mxcsr_quirk_needed(...))
    >
    > but that's unrelated to here and as a note to whoever gets to get to it
    > first.
    >
    >> + const u32 *mxcsr = kbuf + offsetof(struct fxregs_state, mxcsr);
    >> +
    >> + /* Reserved bits in MXCSR must be zero. */
    >> + if (*mxcsr & ~mxcsr_feature_mask)
    >> + return -EINVAL;
    >> + }
    >
    > Btw, that function has another
    >
    > if (xfeatures_mxcsr_quirk(hdr.xfeatures)) {
    >
    > branch already below the loop.
    >
    > Should we merge both? Diff ontop of yours:

    No, because the first usage is wrong. I found that while looking through
    this stuff again. Sigh...

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