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Subject[PATCH v8 07/17] x86/fsgsbase/64: Use FSGSBASE instructions on thread copy and ptrace
Date
When FSGSBASE is enabled, copying threads and reading FS/GS base using
ptrace must read the actual values.

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

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
---

Changes from v7:
* No code change
* Massaged changelog by Andy Lutomirski
---
arch/x86/kernel/process_64.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 4c388817..7e582be 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -429,7 +429,8 @@ 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);
@@ -443,7 +444,8 @@ 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);
@@ -483,10 +485,11 @@ 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));
--
2.7.4
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