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Subject[tip: core/entry] x86: Snapshot thread flags
The following commit has been merged into the core/entry branch of tip:

Commit-ID: 5796ee48d26a18930a8b86fb865ba195282889d0
Gitweb: https://git.kernel.org/tip/5796ee48d26a18930a8b86fb865ba195282889d0
Author: Mark Rutland <mark.rutland@arm.com>
AuthorDate: Wed, 17 Nov 2021 16:30:49
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 26 Nov 2021 21:20:14 +01:00

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/20211117163050.53986-12-mark.rutland@arm.com
---
arch/x86/kernel/process.c | 8 ++++----
arch/x86/kernel/process.h | 4 ++--
arch/x86/mm/tlb.c | 2 +-
3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 04143a6..5d48103 100644
--- 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
--- 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
--- 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;

/*
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