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    Subject[PATCH 5.10 069/101] x86/fpu: Preserve supervisor states in sanitize_restored_user_xstate()
    Date
    From: Thomas Gleixner <tglx@linutronix.de>

    commit 9301982c424a003c0095bf157154a85bf5322bd0 upstream.

    sanitize_restored_user_xstate() preserves the supervisor states only
    when the fx_only argument is zero, which allows unprivileged user space
    to put supervisor states back into init state.

    Preserve them unconditionally.

    [ bp: Fix a typo or two in the text. ]

    Fixes: 5d6b6a6f9b5c ("x86/fpu/xstate: Update sanitize_restored_xstate() for supervisor xstates")
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20210618143444.438635017@linutronix.de
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kernel/fpu/signal.c | 26 ++++++++------------------
    1 file changed, 8 insertions(+), 18 deletions(-)

    diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
    index ec3ae3054792..b7b92cdf3add 100644
    --- a/arch/x86/kernel/fpu/signal.c
    +++ b/arch/x86/kernel/fpu/signal.c
    @@ -221,28 +221,18 @@ sanitize_restored_user_xstate(union fpregs_state *state,

    if (use_xsave()) {
    /*
    - * Note: we don't need to zero the reserved bits in the
    - * xstate_header here because we either didn't copy them at all,
    - * or we checked earlier that they aren't set.
    + * Clear all feature bits which are not set in
    + * user_xfeatures and clear all extended features
    + * for fx_only mode.
    */
    + u64 mask = fx_only ? XFEATURE_MASK_FPSSE : user_xfeatures;

    /*
    - * 'user_xfeatures' might have bits clear which are
    - * set in header->xfeatures. This represents features that
    - * were in init state prior to a signal delivery, and need
    - * to be reset back to the init state. Clear any user
    - * feature bits which are set in the kernel buffer to get
    - * them back to the init state.
    - *
    - * Supervisor state is unchanged by input from userspace.
    - * Ensure supervisor state bits stay set and supervisor
    - * state is not modified.
    + * Supervisor state has to be preserved. The sigframe
    + * restore can only modify user features, i.e. @mask
    + * cannot contain them.
    */
    - if (fx_only)
    - header->xfeatures = XFEATURE_MASK_FPSSE;
    - else
    - header->xfeatures &= user_xfeatures |
    - xfeatures_mask_supervisor();
    + header->xfeatures &= mask | xfeatures_mask_supervisor();
    }

    if (use_fxsr()) {
    --
    2.30.2
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