x86: Snapshot thread flags

Some thread flags can be set remotely, and so even when IRQs are disabled,
the flags can change under our feet. Generally this is unlikely to cause a
problem in practice, but it is somewhat unsound, and KCSAN will
legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20211129130653.2037928-12-mark.rutland@arm.com

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 04143a6..5d48103 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -365,7 +365,7 @@ void arch_setup_new_exec(void)
                clear_thread_flag(TIF_SSBD);
                task_clear_spec_ssb_disable(current);
                task_clear_spec_ssb_noexec(current);
-               speculation_ctrl_update(task_thread_info(current)->flags);
+               speculation_ctrl_update(read_thread_flags());
        }
 }
 
@@ -617,7 +617,7 @@ static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
                        clear_tsk_thread_flag(tsk, TIF_SPEC_IB);
        }
        /* Return the updated threadinfo flags*/
-       return task_thread_info(tsk)->flags;
+       return read_task_thread_flags(tsk);
 }
 
 void speculation_ctrl_update(unsigned long tif)
@@ -653,8 +653,8 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
 {
        unsigned long tifp, tifn;
 
-       tifn = READ_ONCE(task_thread_info(next_p)->flags);
-       tifp = READ_ONCE(task_thread_info(prev_p)->flags);
+       tifn = read_task_thread_flags(next_p);
+       tifp = read_task_thread_flags(prev_p);
 
        switch_to_bitmap(tifp);
 

diff --git a/arch/x86/kernel/process.h b/arch/x86/kernel/process.h
index 1d0797b..76b547b 100644 (file)
--- a/arch/x86/kernel/process.h
+++ b/arch/x86/kernel/process.h
@@ -13,8 +13,8 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p);
 static inline void switch_to_extra(struct task_struct *prev,
                                   struct task_struct *next)
 {
-       unsigned long next_tif = task_thread_info(next)->flags;
-       unsigned long prev_tif = task_thread_info(prev)->flags;
+       unsigned long next_tif = read_task_thread_flags(next);
+       unsigned long prev_tif = read_task_thread_flags(prev);
 
        if (IS_ENABLED(CONFIG_SMP)) {
                /*

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 59ba296..92bb03b 100644 (file)
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -361,7 +361,7 @@ static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm,
 
 static unsigned long mm_mangle_tif_spec_bits(struct task_struct *next)
 {
-       unsigned long next_tif = task_thread_info(next)->flags;
+       unsigned long next_tif = read_task_thread_flags(next);
        unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK;
 
        /*