lkml.org 
[lkml]   [2021]   [Jun]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.12 145/178] x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer
    Date
    From: Andy Lutomirski <luto@kernel.org>

    commit d8778e393afa421f1f117471144f8ce6deb6953a upstream.

    Both Intel and AMD consider it to be architecturally valid for XRSTOR to
    fail with #PF but nonetheless change the register state. The actual
    conditions under which this might occur are unclear [1], but it seems
    plausible that this might be triggered if one sibling thread unmaps a page
    and invalidates the shared TLB while another sibling thread is executing
    XRSTOR on the page in question.

    __fpu__restore_sig() can execute XRSTOR while the hardware registers
    are preserved on behalf of a different victim task (using the
    fpu_fpregs_owner_ctx mechanism), and, in theory, XRSTOR could fail but
    modify the registers.

    If this happens, then there is a window in which __fpu__restore_sig()
    could schedule out and the victim task could schedule back in without
    reloading its own FPU registers. This would result in part of the FPU
    state that __fpu__restore_sig() was attempting to load leaking into the
    victim task's user-visible state.

    Invalidate preserved FPU registers on XRSTOR failure to prevent this
    situation from corrupting any state.

    [1] Frequent readers of the errata lists might imagine "complex
    microarchitectural conditions".

    Fixes: 1d731e731c4c ("x86/fpu: Add a fastpath to __fpu__restore_sig()")
    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
    Acked-by: Rik van Riel <riel@surriel.com>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20210608144345.758116583@linutronix.de
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kernel/fpu/signal.c | 19 +++++++++++++++++++
    1 file changed, 19 insertions(+)

    --- a/arch/x86/kernel/fpu/signal.c
    +++ b/arch/x86/kernel/fpu/signal.c
    @@ -369,6 +369,25 @@ static int __fpu__restore_sig(void __use
    fpregs_unlock();
    return 0;
    }
    +
    + /*
    + * The above did an FPU restore operation, restricted to
    + * the user portion of the registers, and failed, but the
    + * microcode might have modified the FPU registers
    + * nevertheless.
    + *
    + * If the FPU registers do not belong to current, then
    + * invalidate the FPU register state otherwise the task might
    + * preempt current and return to user space with corrupted
    + * FPU registers.
    + *
    + * In case current owns the FPU registers then no further
    + * action is required. The fixup below will handle it
    + * correctly.
    + */
    + if (test_thread_flag(TIF_NEED_FPU_LOAD))
    + __cpu_invalidate_fpregs_state();
    +
    fpregs_unlock();
    } else {
    /*

    \
     
     \ /
      Last update: 2021-06-21 18:49    [W:2.848 / U:0.344 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site