[PATCH v2] arm64: lockdep: enable checks for held locks when returning to userspace

[PATCH v2] arm64: lockdep: enable checks for held locks when returning to userspace

[Eric Chan]

Currently arm64 doesn't use CONFIG_GENERIC_ENTRY and doesn't call
lockdep_sys_exit() when returning to userspace.
This means that lockdep won't check for held locks when
returning to userspace, which would be useful to detect kernel bugs.

Call lockdep_sys_exit() when returning to userspace,
enabling checking for held locks.

At the same time, rename arm64's prepare_exit_to_user_mode() to
exit_to_user_mode_prepare() to more clearly align with the naming
in the generic entry code.

Signed-off-by: Eric Chan <ericchancf@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
---
 arch/arm64/kernel/entry-common.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 3af3c01c93a6..9d6827201b6c 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -126,7 +126,7 @@ static __always_inline void __exit_to_user_mode(void)
 	lockdep_hardirqs_on(CALLER_ADDR0);
 }
 
-static __always_inline void prepare_exit_to_user_mode(struct pt_regs *regs)
+static __always_inline void exit_to_user_mode_prepare(struct pt_regs *regs)
 {
 	unsigned long flags;
 
@@ -135,11 +135,13 @@ static __always_inline void prepare_exit_to_user_mode(struct pt_regs *regs)
 	flags = read_thread_flags();
 	if (unlikely(flags & _TIF_WORK_MASK))
 		do_notify_resume(regs, flags);
+
+	lockdep_sys_exit();
 }
 
 static __always_inline void exit_to_user_mode(struct pt_regs *regs)
 {
-	prepare_exit_to_user_mode(regs);
+	exit_to_user_mode_prepare(regs);
 	mte_check_tfsr_exit();
 	__exit_to_user_mode();
 }
-- 
2.41.0.rc0.172.g3f132b7071-goog
V1 -> V2 : Revise the commit message to make it clearer and avoid any misleading information.

Re: [PATCH v2] arm64: lockdep: enable checks for held locks when returning to userspace

[Catalin Marinas]

On Wed, 31 May 2023 09:09:09 +0000, Eric Chan wrote:
> Currently arm64 doesn't use CONFIG_GENERIC_ENTRY and doesn't call
> lockdep_sys_exit() when returning to userspace.
> This means that lockdep won't check for held locks when
> returning to userspace, which would be useful to detect kernel bugs.
> 
> Call lockdep_sys_exit() when returning to userspace,
> enabling checking for held locks.
> 
> [...]

Applied to arm64 (for-next/misc), thanks!

[1/1] arm64: lockdep: enable checks for held locks when returning to userspace
      https://git.kernel.org/arm64/c/ab1e29acdb33

-- 
Catalin