[PATCH AUTOSEL 5.2 095/185] arm64: entry: Move ct_user_exit before any other exception

Sasha Levin
2019-09-22T18:52:19Z

From: James Morse <james.morse@arm.com>

[ Upstream commit 2671828c3ff4ffadf777f793a1f3232d6e51394a ]

When taking an SError or Debug exception from EL0, we run the C
handler for these exceptions before updating the context tracking
code and unmasking lower priority interrupts.

When booting with nohz_full lockdep tells us we got this wrong:
| =============================
| WARNING: suspicious RCU usage
| 5.3.0-rc2-00010-gb4b5e9dcb11b-dirty #11271 Not tainted
| -----------------------------
| include/linux/rcupdate.h:643 rcu_read_unlock() used illegally wh!
|
| other info that might help us debug this:
|
|
| RCU used illegally from idle CPU!
| rcu_scheduler_active = 2, debug_locks = 1
| RCU used illegally from extended quiescent state!
| 1 lock held by a.out/432:
| #0: 00000000c7a79515 (rcu_read_lock){....}, at: brk_handler+0x00
|
| stack backtrace:
| CPU: 1 PID: 432 Comm: a.out Not tainted 5.3.0-rc2-00010-gb4b5e9d1
| Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno De8
| Call trace:
| dump_backtrace+0x0/0x140
| show_stack+0x14/0x20
| dump_stack+0xbc/0x104
| lockdep_rcu_suspicious+0xf8/0x108
| brk_handler+0x164/0x1b0
| do_debug_exception+0x11c/0x278
| el0_dbg+0x14/0x20

Moving the ct_user_exit calls to be before do_debug_exception() means
they are also before trace_hardirqs_off() has been updated. Add a new
ct_user_exit_irqoff macro to avoid the context-tracking code using
irqsave/restore before we've updated trace_hardirqs_off(). To be
consistent, do this everywhere.

The C helper is called enter_from_user_mode() to match x86 in the hope
we can merge them into kernel/context_tracking.c later.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 6c81fe7925cc4c42 ("arm64: enable context tracking")
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/exception.h | 2 ++
arch/arm64/kernel/entry.S | 36 ++++++++++++++++--------------
arch/arm64/kernel/traps.c | 9 ++++++++
3 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/include/asm/exception.h b/arch/arm64/include/asm/exception.h
index ed57b760f38cf..a17393ff66774 100644
--- a/arch/arm64/include/asm/exception.h
+++ b/arch/arm64/include/asm/exception.h
@@ -30,4 +30,6 @@ static inline u32 disr_to_esr(u64 disr)
return esr;
}

+asmlinkage void enter_from_user_mode(void);
+
#endif /* __ASM_EXCEPTION_H */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 320a30dbe35ef..84a822748c84e 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -30,9 +30,9 @@
* Context tracking subsystem. Used to instrument transitions
* between user and kernel mode.
*/
- .macro ct_user_exit
+ .macro ct_user_exit_irqoff
#ifdef CONFIG_CONTEXT_TRACKING
- bl context_tracking_user_exit
+ bl enter_from_user_mode
#endif
.endm

@@ -792,8 +792,8 @@ el0_cp15:
/*
* Trapped CP15 (MRC, MCR, MRRC, MCRR) instructions
*/
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, x25
mov x1, sp
bl do_cp15instr
@@ -805,8 +805,8 @@ el0_da:
* Data abort handling
*/
mrs x26, far_el1
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
clear_address_tag x0, x26
mov x1, x25
mov x2, sp
@@ -818,11 +818,11 @@ el0_ia:
*/
mrs x26, far_el1
gic_prio_kentry_setup tmp=x0
+ ct_user_exit_irqoff
enable_da_f
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_off
#endif
- ct_user_exit
mov x0, x26
mov x1, x25
mov x2, sp
@@ -832,8 +832,8 @@ el0_fpsimd_acc:
/*
* Floating Point or Advanced SIMD access
*/
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, x25
mov x1, sp
bl do_fpsimd_acc
@@ -842,8 +842,8 @@ el0_sve_acc:
/*
* Scalable Vector Extension access
*/
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, x25
mov x1, sp
bl do_sve_acc
@@ -852,8 +852,8 @@ el0_fpsimd_exc:
/*
* Floating Point, Advanced SIMD or SVE exception
*/
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, x25
mov x1, sp
bl do_fpsimd_exc
@@ -868,11 +868,11 @@ el0_sp_pc:
* Stack or PC alignment exception handling
*/
gic_prio_kentry_setup tmp=x0
+ ct_user_exit_irqoff
enable_da_f
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_off
#endif
- ct_user_exit
mov x0, x26
mov x1, x25
mov x2, sp
@@ -882,8 +882,8 @@ el0_undef:
/*
* Undefined instruction
*/
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, sp
bl do_undefinstr
b ret_to_user
@@ -891,8 +891,8 @@ el0_sys:
/*
* System instructions, for trapped cache maintenance instructions
*/
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, x25
mov x1, sp
bl do_sysinstr
@@ -902,17 +902,18 @@ el0_dbg:
* Debug exception handling
*/
tbnz x24, #0, el0_inv // EL0 only
+ mrs x24, far_el1
gic_prio_kentry_setup tmp=x3
- mrs x0, far_el1
+ ct_user_exit_irqoff
+ mov x0, x24
mov x1, x25
mov x2, sp
bl do_debug_exception
enable_da_f
- ct_user_exit
b ret_to_user
el0_inv:
+ ct_user_exit_irqoff
enable_daif
- ct_user_exit
mov x0, sp
mov x1, #BAD_SYNC
mov x2, x25
@@ -925,13 +926,13 @@ el0_irq:
kernel_entry 0
el0_irq_naked:
gic_prio_irq_setup pmr=x20, tmp=x0
+ ct_user_exit_irqoff
enable_da_f

#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_off
#endif

- ct_user_exit
#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
tbz x22, #55, 1f
bl do_el0_irq_bp_hardening
@@ -958,13 +959,14 @@ ENDPROC(el1_error)
el0_error:
kernel_entry 0
el0_error_naked:
- mrs x1, esr_el1
+ mrs x25, esr_el1
gic_prio_kentry_setup tmp=x2
+ ct_user_exit_irqoff
enable_dbg
mov x0, sp
+ mov x1, x25
bl do_serror
enable_da_f
- ct_user_exit
b ret_to_user
ENDPROC(el0_error)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 985721a1264c9..b6706a8860371 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -7,9 +7,11 @@
*/

#include <linux/bug.h>
+#include <linux/context_tracking.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/kallsyms.h>
+#include <linux/kprobes.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
#include <linux/hardirq.h>
@@ -905,6 +907,13 @@ asmlinkage void do_serror(struct pt_regs *regs, unsigned int esr)
nmi_exit();
}

+asmlinkage void enter_from_user_mode(void)
+{
+ CT_WARN_ON(ct_state() != CONTEXT_USER);
+ user_exit_irqoff();
+}
+NOKPROBE_SYMBOL(enter_from_user_mode);
+
void __pte_error(const char *file, int line, unsigned long val)
{
pr_err("%s:%d: bad pte %016lx.\n", file, line, val);
--
2.20.1