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    Subject[PATCH v13 07/16] x86/process/64: Use FSGSBASE instructions on thread copy and ptrace
    Date
    From: "Chang S. Bae" <chang.seok.bae@intel.com>

    When FSGSBASE is enabled, copying threads and reading fsbase and gsbase
    using ptrace must read the actual values.

    When copying a thread, use save_fsgs() and copy the saved values. For
    ptrace, the bases must be read from memory regardless of the selector if
    FSGSBASE is enabled.

    [ tglx: Invoke __rdgsbase_inactive() with interrupts disabled ]
    [ luto: Massage changelog ]

    Suggested-by: Andy Lutomirski <luto@kernel.org>
    Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: "H . Peter Anvin" <hpa@zytor.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Ravi Shankar <ravi.v.shankar@intel.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Link: https://lkml.kernel.org/r/1557309753-24073-9-git-send-email-chang.seok.bae@intel.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kernel/process.c | 10 ++++++----
    arch/x86/kernel/process_64.c | 6 ++++--
    2 files changed, 10 insertions(+), 6 deletions(-)

    diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
    index 9da70b279dad..0264d9bb8991 100644
    --- a/arch/x86/kernel/process.c
    +++ b/arch/x86/kernel/process.c
    @@ -140,10 +140,12 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
    memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));

    #ifdef CONFIG_X86_64
    - savesegment(gs, p->thread.gsindex);
    - p->thread.gsbase = p->thread.gsindex ? 0 : current->thread.gsbase;
    - savesegment(fs, p->thread.fsindex);
    - p->thread.fsbase = p->thread.fsindex ? 0 : current->thread.fsbase;
    + current_save_fsgs();
    + p->thread.fsindex = current->thread.fsindex;
    + p->thread.fsbase = current->thread.fsbase;
    + p->thread.gsindex = current->thread.gsindex;
    + p->thread.gsbase = current->thread.gsbase;
    +
    savesegment(es, p->thread.es);
    savesegment(ds, p->thread.ds);
    #else
    diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    index aefb30bc56bc..0bcb48a1264a 100644
    --- a/arch/x86/kernel/process_64.c
    +++ b/arch/x86/kernel/process_64.c
    @@ -423,7 +423,8 @@ unsigned long x86_fsbase_read_task(struct task_struct *task)

    if (task == current)
    fsbase = x86_fsbase_read_cpu();
    - else if (task->thread.fsindex == 0)
    + else if (static_cpu_has(X86_FEATURE_FSGSBASE) ||
    + (task->thread.fsindex == 0))
    fsbase = task->thread.fsbase;
    else
    fsbase = x86_fsgsbase_read_task(task, task->thread.fsindex);
    @@ -437,7 +438,8 @@ unsigned long x86_gsbase_read_task(struct task_struct *task)

    if (task == current)
    gsbase = x86_gsbase_read_cpu_inactive();
    - else if (task->thread.gsindex == 0)
    + else if (static_cpu_has(X86_FEATURE_FSGSBASE) ||
    + (task->thread.gsindex == 0))
    gsbase = task->thread.gsbase;
    else
    gsbase = x86_fsgsbase_read_task(task, task->thread.gsindex);
    --
    2.25.1
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