lkml.org 
[lkml]   [2021]   [Oct]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.14 147/151] x86/fpu: Restore the masking out of reserved MXCSR bits
    Date
    From: Borislav Petkov <bp@suse.de>

    commit d298b03506d3e161f7492c440babb0bfae35e650 upstream.

    Ser Olmy reported a boot failure:

    init[1] bad frame in sigreturn frame:(ptrval) ip:b7c9fbe6 sp:bf933310 orax:ffffffff \
    in libc-2.33.so[b7bed000+156000]
    Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
    CPU: 0 PID: 1 Comm: init Tainted: G W 5.14.9 #1
    Hardware name: Hewlett-Packard HP PC/HP Board, BIOS JD.00.06 12/06/2001
    Call Trace:
    dump_stack_lvl
    dump_stack
    panic
    do_exit.cold
    do_group_exit
    get_signal
    arch_do_signal_or_restart
    ? force_sig_info_to_task
    ? force_sig
    exit_to_user_mode_prepare
    syscall_exit_to_user_mode
    do_int80_syscall_32
    entry_INT80_32

    on an old 32-bit Intel CPU:

    vendor_id : GenuineIntel
    cpu family : 6
    model : 6
    model name : Celeron (Mendocino)
    stepping : 5
    microcode : 0x3

    Ser bisected the problem to the commit in Fixes.

    tglx suggested reverting the rejection of invalid MXCSR values which
    this commit introduced and replacing it with what the old code did -
    simply masking them out to zero.

    Further debugging confirmed his suggestion:

    fpu->state.fxsave.mxcsr: 0xb7be13b4, mxcsr_feature_mask: 0xffbf
    WARNING: CPU: 0 PID: 1 at arch/x86/kernel/fpu/signal.c:384 __fpu_restore_sig+0x51f/0x540

    so restore the original behavior only for 32-bit kernels where you have
    ancient machines with buggy hardware. For 32-bit programs on 64-bit
    kernels, user space which supplies wrong MXCSR values is considered
    malicious so fail the sigframe restoration there.

    Fixes: 6f9866a166cd ("x86/fpu/signal: Let xrstor handle the features to init")
    Reported-by: Ser Olmy <ser.olmy@protonmail.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Tested-by: Ser Olmy <ser.olmy@protonmail.com>
    Cc: <stable@vger.kernel.org>
    Link: https://lkml.kernel.org/r/YVtA67jImg3KlBTw@zn.tnic
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kernel/fpu/signal.c | 11 ++++++++---
    1 file changed, 8 insertions(+), 3 deletions(-)

    --- a/arch/x86/kernel/fpu/signal.c
    +++ b/arch/x86/kernel/fpu/signal.c
    @@ -379,9 +379,14 @@ static int __fpu_restore_sig(void __user
    sizeof(fpu->state.fxsave)))
    return -EFAULT;

    - /* Reject invalid MXCSR values. */
    - if (fpu->state.fxsave.mxcsr & ~mxcsr_feature_mask)
    - return -EINVAL;
    + if (IS_ENABLED(CONFIG_X86_64)) {
    + /* Reject invalid MXCSR values. */
    + if (fpu->state.fxsave.mxcsr & ~mxcsr_feature_mask)
    + return -EINVAL;
    + } else {
    + /* Mask invalid bits out for historical reasons (broken hardware). */
    + fpu->state.fxsave.mxcsr &= ~mxcsr_feature_mask;
    + }

    /* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */
    if (use_xsave())

    \
     
     \ /
      Last update: 2021-10-11 16:14    [W:4.128 / U:0.196 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site