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From: Mark Rutland <mark.rutland@arm.com>
To: linux-kernel@vger.kernel.org
Cc: benh@kernel.crashing.org, boqun.feng@gmail.com, bp@alien8.de,
	catalin.marinas@arm.com, dvyukov@google.com, elver@google.com,
	ink@jurassic.park.msu.ru, jonas@southpole.se,
	juri.lelli@redhat.com, linux@armlinux.org.uk, luto@kernel.org,
	mark.rutland@arm.com, mattst88@gmail.com, mingo@redhat.com,
	monstr@monstr.eu, mpe@ellerman.id.au, paulmck@kernel.org,
	paulus@samba.org, peterz@infradead.org, rth@twiddle.net,
	shorne@gmail.com, stefan.kristiansson@saunalahti.fi,
	tglx@linutronix.de, vincent.guittot@linaro.org, will@kernel.org
Subject: [PATCH v4 10/10] x86: snapshot thread flags
Date: Tue,  3 Aug 2021 10:54:28 +0100	[thread overview]
Message-ID: <20210803095428.17009-11-mark.rutland@arm.com> (raw)
In-Reply-To: <20210803095428.17009-1-mark.rutland@arm.com>

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>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@redhat.com>
---
 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


  parent reply	other threads:[~2021-08-03  9:56 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03  9:54 [PATCH v4 00/10] thread_info: use helpers to " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 01/10] thread_info: add " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 02/10] entry: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 03/10] sched: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 04/10] alpha: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 05/10] arm: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 06/10] arm64: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 07/10] microblaze: " Mark Rutland
2021-08-25  9:03   ` Michal Simek
2021-08-03  9:54 ` [PATCH v4 08/10] openrisc: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 09/10] powerpc: " Mark Rutland
2021-08-03  9:54 ` Mark Rutland [this message]
2021-08-03 16:01 ` [PATCH v4 00/10] thread_info: use helpers to " Paul E. McKenney

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