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    Subject[patch 20/71] x64, fpu: fix possible FPU leakage in error conditions

    2.6.26-stable review patch. If anyone has any objections, please let us
    know.

    ------------------
    From: Suresh Siddha <suresh.b.siddha@intel.com>

    [Upstream commit: 6ffac1e90a17ea0aded5c581204397421eec91b6]

    On Thu, Jul 24, 2008 at 03:43:44PM -0700, Linus Torvalds wrote:
    > So how about this patch as a starting point? This is the RightThing(tm) to
    > do regardless, and if it then makes it easier to do some other cleanups,
    > we should do it first. What do you think?

    restore_fpu_checking() calls init_fpu() in error conditions.

    While this is wrong(as our main intention is to clear the fpu state of
    the thread), this was benign before commit 92d140e21f1 ("x86: fix taking
    DNA during 64bit sigreturn").

    Post commit 92d140e21f1, live FPU registers may not belong to this
    process at this error scenario.

    In the error condition for restore_fpu_checking() (especially during the
    64bit signal return), we are doing init_fpu(), which saves the live FPU
    register state (possibly belonging to some other process context) into
    the thread struct (through unlazy_fpu() in init_fpu()). This is wrong
    and can leak the FPU data.

    For the signal handler restore error condition in restore_i387(), clear
    the fpu state present in the thread struct(before ultimately sending a
    SIGSEGV for badframe).

    For the paranoid error condition check in math_state_restore(), send a
    SIGSEGV, if we fail to restore the state.

    Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    arch/x86/kernel/signal_64.c | 11 ++++++++++-
    arch/x86/kernel/traps_64.c | 9 ++++++++-
    include/asm-x86/i387.h | 2 --
    3 files changed, 18 insertions(+), 4 deletions(-)

    --- a/arch/x86/kernel/signal_64.c
    +++ b/arch/x86/kernel/signal_64.c
    @@ -104,7 +104,16 @@ static inline int restore_i387(struct _f
    clts();
    task_thread_info(current)->status |= TS_USEDFPU;
    }
    - return restore_fpu_checking((__force struct i387_fxsave_struct *)buf);
    + err = restore_fpu_checking((__force struct i387_fxsave_struct *)buf);
    + if (unlikely(err)) {
    + /*
    + * Encountered an error while doing the restore from the
    + * user buffer, clear the fpu state.
    + */
    + clear_fpu(tsk);
    + clear_used_math();
    + }
    + return err;
    }

    /*
    --- a/arch/x86/kernel/traps_64.c
    +++ b/arch/x86/kernel/traps_64.c
    @@ -1141,7 +1141,14 @@ asmlinkage void math_state_restore(void)
    }

    clts(); /* Allow maths ops (or we recurse) */
    - restore_fpu_checking(&me->thread.xstate->fxsave);
    + /*
    + * Paranoid restore. send a SIGSEGV if we fail to restore the state.
    + */
    + if (unlikely(restore_fpu_checking(&me->thread.xstate->fxsave))) {
    + stts();
    + force_sig(SIGSEGV, me);
    + return;
    + }
    task_thread_info(me)->status |= TS_USEDFPU;
    me->fpu_counter++;
    }
    --- a/include/asm-x86/i387.h
    +++ b/include/asm-x86/i387.h
    @@ -63,8 +63,6 @@ static inline int restore_fpu_checking(s
    #else
    : [fx] "cdaSDb" (fx), "m" (*fx), "0" (0));
    #endif
    - if (unlikely(err))
    - init_fpu(current);
    return err;
    }

    --


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