[PATCH v3 10/10] x86: snapshot thread flags
From: Mark Rutland
Date: Tue Jul 13 2021 - 07:39:50 EST
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@xxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/process.c | 8 ++++----
arch/x86/kernel/process.h | 6 +++---
arch/x86/mm/tlb.c | 2 +-
3 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1d9463e3096b..0b9a1f2ccfb3 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -348,7 +348,7 @@ 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());
}
}
@@ -600,7 +600,7 @@ 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)
@@ -636,8 +636,8 @@ 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 1d0797b2338a..0b1be8685b49 100644
--- a/arch/x86/kernel/process.h
+++ b/arch/x86/kernel/process.h
@@ -13,9 +13,9 @@ 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)) {
/*
* Avoid __switch_to_xtra() invocation when conditional
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index cfe6b1e85fa6..56917e92991d 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -319,7 +319,7 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
static unsigned long mm_mangle_tif_spec_ib(struct task_struct *next)
{
- unsigned long next_tif = task_thread_info(next)->flags;
+ unsigned long next_tif = read_task_thread_flags(next);
unsigned long ibpb = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_IBPB;
return (unsigned long)next->mm | ibpb;
--
2.11.0