Commit f60a83df authored by Chang S. Bae's avatar Chang S. Bae Committed by Thomas Gleixner
Browse files

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: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarThomas 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
parent 1ab5f3f7

arch/x86/kernel/process_64.c

+13 −6
Original line number Diff line number Diff line
@@ -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));

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