From: Mark Rutland <mark.rutland@xxxxxxx>
[ Upstream commit 46b0567c851cf85d6ba6f23eef385ec9111d09bc ]
Commit 6c81fe7925cc4c42 ("arm64: enable context tracking") did not
update el0_sp_pc to use ct_user_exit, but this appears to have been
unintentional. In commit 6ab6463aeb5fbc75 ("arm64: adjust el0_sync so
that a function can be called") we made x0 available, and in the return
to userspace we call ct_user_enter in the kernel_exit macro.
Due to this, we currently don't correctly inform RCU of the user->kernel
transition, and may erroneously account for time spent in the kernel as
if we were in an extended quiescent state when CONFIG_CONTEXT_TRACKING
is enabled.
As we do record the kernel->user transition, a userspace application
making accesses from an unaligned stack pointer can demonstrate the
imbalance, provoking the following warning:
------------[ cut here ]------------
WARNING: CPU: 2 PID: 3660 at kernel/context_tracking.c:75 context_tracking_enter+0xd8/0xe4()
Modules linked in:
CPU: 2 PID: 3660 Comm: a.out Not tainted 4.1.0-rc7+ #8
Hardware name: ARM Juno development board (r0) (DT)
Call trace:
[<ffffffc000089914>] dump_backtrace+0x0/0x124
[<ffffffc000089a48>] show_stack+0x10/0x1c
[<ffffffc0005b3cbc>] dump_stack+0x84/0xc8
[<ffffffc0000b3214>] warn_slowpath_common+0x98/0xd0
[<ffffffc0000b330c>] warn_slowpath_null+0x14/0x20
[<ffffffc00013ada4>] context_tracking_enter+0xd4/0xe4
[<ffffffc0005b534c>] preempt_schedule_irq+0xd4/0x114
[<ffffffc00008561c>] el1_preempt+0x4/0x28
[<ffffffc0001b8040>] exit_files+0x38/0x4c
[<ffffffc0000b5b94>] do_exit+0x430/0x978
[<ffffffc0000b614c>] do_group_exit+0x40/0xd4
[<ffffffc0000c0208>] get_signal+0x23c/0x4f4
[<ffffffc0000890b4>] do_signal+0x1ac/0x518
[<ffffffc000089650>] do_notify_resume+0x5c/0x68
---[ end trace 963c192600337066 ]---
This patch adds the missing ct_user_exit to the el0_sp_pc entry path,
correcting the context tracking for this case.
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Fixes: 6c81fe7925cc ("arm64: enable context tracking")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.17+
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
arch/arm64/kernel/entry.S | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 2b0f3d5..6c99b46 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -517,6 +517,7 @@ el0_sp_pc:
mrs x26, far_el1
// enable interrupts before calling the main handler
enable_dbg_and_irq
+ ct_user_exit
mov x0, x26
mov x1, x25
mov x2, sp
--
2.1.0
--
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