x86/process/64: Use FSGSBASE instructions on thread copy and ptrace

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

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 59013f480b8664cfe42ea1a08d03ceade0690c44..8f239091c15d43c15274e551028de9e65815d876 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -245,13 +245,17 @@ static __always_inline void save_fsgs(struct task_struct *task)
        savesegment(fs, task->thread.fsindex);
        savesegment(gs, task->thread.gsindex);
        if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
+               unsigned long flags;
+
                /*
                 * If FSGSBASE is enabled, we can't make any useful guesses
                 * about the base, and user code expects us to save the current
                 * value.  Fortunately, reading the base directly is efficient.
                 */
                task->thread.fsbase = rdfsbase();
+               local_irq_save(flags);
                task->thread.gsbase = __rdgsbase_inactive();
+               local_irq_restore(flags);
        } else {
                save_base_legacy(task, task->thread.fsindex, FS);
                save_base_legacy(task, task->thread.gsindex, GS);
@@ -433,7 +437,8 @@ 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);
@@ -447,7 +452,8 @@ 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);
@@ -487,10 +493,11 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
        p->thread.sp = (unsigned long) fork_frame;
        p->thread.io_bitmap_ptr = NULL;
 
-       savesegment(gs, p->thread.gsindex);
-       p->thread.gsbase = p->thread.gsindex ? 0 : me->thread.gsbase;
-       savesegment(fs, p->thread.fsindex);
-       p->thread.fsbase = p->thread.fsindex ? 0 : me->thread.fsbase;
+       save_fsgs(me);
+       p->thread.fsindex = me->thread.fsindex;
+       p->thread.fsbase = me->thread.fsbase;
+       p->thread.gsindex = me->thread.gsindex;
+       p->thread.gsbase = me->thread.gsbase;
        savesegment(es, p->thread.es);
        savesegment(ds, p->thread.ds);
        memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));