From: "Chang S. Bae" <[email protected]> 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 <[email protected]> Signed-off-by: Chang S. Bae <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Reviewed-by: Tony Luck <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Tony Luck <[email protected]> Cc: Andi Kleen <[email protected]> --- arch/x86/kernel/process.c | 9 +++++---- arch/x86/kernel/process_64.c | 6 ++++-- 2 files changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 9da70b279dad8..31dd24f9c8d8e 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -140,10 +140,11 @@ 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; + save_fsgs(current); + 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 4be88124d81ea..57cdbbb0381ac 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -346,7 +346,8 @@ 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); @@ -360,7 +361,8 @@ 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); -- 2.20.1
