| Message ID | 156378173770.12011.3832608237079432765.stgit@devnote2 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: kprobes: Fix some bugs in arm64 kprobes | expand |
On Mon, Jul 22, 2019 at 04:48:58PM +0900, Masami Hiramatsu wrote: > Make debug exceptions visible from RCU so that synchronize_rcu() > correctly track the debug exception handler. > > This also introduces sanity checks for user-mode exceptions as same > as x86's ist_enter()/ist_exit(). > > The debug exception can interrupt in idle task. For example, it warns > if we put a kprobe on a function called from idle task as below. > The warning message showed that the rcu_read_lock() caused this > problem. But actually, this means the RCU is lost the context which > is already in NMI/IRQ. > > /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events > /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable > /sys/kernel/debug/tracing # [ 135.122237] > [ 135.125035] ============================= > [ 135.125310] WARNING: suspicious RCU usage > [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted > [ 135.125904] ----------------------------- > [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! > [ 135.126839] > [ 135.126839] other info that might help us debug this: > [ 135.126839] > [ 135.127410] > [ 135.127410] RCU used illegally from idle CPU! > [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 > [ 135.128114] RCU used illegally from extended quiescent state! > [ 135.128555] 1 lock held by swapper/0/0: > [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 > [ 135.130499] > [ 135.130499] stack backtrace: > [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 > [ 135.131841] Hardware name: linux,dummy-virt (DT) > [ 135.132224] Call trace: > [ 135.132491] dump_backtrace+0x0/0x140 > [ 135.132806] show_stack+0x24/0x30 > [ 135.133133] dump_stack+0xc4/0x10c > [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 > [ 135.134171] call_break_hook+0x170/0x178 > [ 135.134486] brk_handler+0x28/0x68 > [ 135.134792] do_debug_exception+0x90/0x150 > [ 135.135051] el1_dbg+0x18/0x8c > [ 135.135260] default_idle_call+0x0/0x44 > [ 135.135516] cpu_startup_entry+0x2c/0x30 > [ 135.135815] rest_init+0x1b0/0x280 > [ 135.136044] arch_call_rest_init+0x14/0x1c > [ 135.136305] start_kernel+0x4d4/0x500 > [ 135.136597] > > So make debug exception visible to RCU can fix this warning. > > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > Cc: Paul E. McKenney <paulmck@linux.ibm.com> From an RCU viewpoint: Acked-by: Paul E. McKenney <paulmck@linux.ibm.com> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > --- > arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 9568c116ac7f..a6b244240db6 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > debug_fault_info[nr].name = name; > } > > +/* > + * In debug exception context, we explicitly disable preemption. > + * This serves two purposes: it makes it much less likely that we would > + * accidentally schedule in exception context and it will force a warning > + * if we somehow manage to schedule by accident. > + */ > +static void debug_exception_enter(struct pt_regs *regs) > +{ > + if (user_mode(regs)) { > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + } else { > + /* > + * We might have interrupted pretty much anything. In > + * fact, if we're a debug exception, we can even interrupt > + * NMI processing. We don't want in_nmi() to return true, > + * but we need to notify RCU. > + */ > + rcu_nmi_enter(); > + } > + > + preempt_disable(); > + > + /* This code is a bit fragile. Test it. */ > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); > +} > +NOKPROBE_SYMBOL(debug_exception_enter); > + > +static void debug_exception_exit(struct pt_regs *regs) > +{ > + preempt_enable_no_resched(); > + > + if (!user_mode(regs)) > + rcu_nmi_exit(); > +} > +NOKPROBE_SYMBOL(debug_exception_exit); > + > #ifdef CONFIG_ARM64_ERRATUM_1463225 > DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); > > @@ -824,6 +860,8 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, > if (interrupts_enabled(regs)) > trace_hardirqs_off(); > > + debug_exception_enter(regs); > + > if (user_mode(regs) && !is_ttbr0_addr(pc)) > arm64_apply_bp_hardening(); > > @@ -832,6 +870,8 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, > inf->sig, inf->code, (void __user *)pc, esr); > } > > + debug_exception_exit(regs); > + > if (interrupts_enabled(regs)) > trace_hardirqs_on(); > } >
Hi, On 22/07/2019 08:48, Masami Hiramatsu wrote: > Make debug exceptions visible from RCU so that synchronize_rcu() > correctly track the debug exception handler. > > This also introduces sanity checks for user-mode exceptions as same > as x86's ist_enter()/ist_exit(). > > The debug exception can interrupt in idle task. For example, it warns > if we put a kprobe on a function called from idle task as below. > The warning message showed that the rcu_read_lock() caused this > problem. But actually, this means the RCU is lost the context which > is already in NMI/IRQ. > So make debug exception visible to RCU can fix this warning. > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 9568c116ac7f..a6b244240db6 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > debug_fault_info[nr].name = name; > } > > +/* > + * In debug exception context, we explicitly disable preemption. > + * This serves two purposes: it makes it much less likely that we would > + * accidentally schedule in exception context and it will force a warning > + * if we somehow manage to schedule by accident. > + */ > +static void debug_exception_enter(struct pt_regs *regs) > +{ > + if (user_mode(regs)) { > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); Would moving entry.S's context_tracking_user_exit() call to be before do_debug_exception() also fix this? I don't know the reason its done 'after' debug exception handling. Its always been like this: commit 6c81fe7925cc4c42 ("arm64: enable context tracking"). > + } else { > + /* > + * We might have interrupted pretty much anything. In > + * fact, if we're a debug exception, we can even interrupt > + * NMI processing. > + * We don't want in_nmi() to return true, > + * but we need to notify RCU. How come? If you interrupted an SError or pseudo-nmi, it already is. Those paths should all be painted no-kprobe, but I'm sure there are gaps. The hw-breakpoints can almost certainly hook them. > + */ > + rcu_nmi_enter(); Can we interrupt printk()? Do we need printk_nmi_enter()? ... What about ftrace? Because SError and pseudo-nmi can interrupt interrupt-masked code, we describe them as NMI. The only difference here is these exceptions are synchronous. I suspect we should make these debug exceptions nmi for EL1. We can then use this for the kprobe-re-entrance stuff so the pre/post hooks don't get run if they interrupted something also described as NMI. > + } > + > + preempt_disable(); > + > + /* This code is a bit fragile. Test it. */ > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); > +} > +NOKPROBE_SYMBOL(debug_exception_enter); Thanks, James
On Tue, 23 Jul 2019 18:07:56 +0100 James Morse <james.morse@arm.com> wrote: > Hi, > > On 22/07/2019 08:48, Masami Hiramatsu wrote: > > Make debug exceptions visible from RCU so that synchronize_rcu() > > correctly track the debug exception handler. > > > > This also introduces sanity checks for user-mode exceptions as same > > as x86's ist_enter()/ist_exit(). > > > > The debug exception can interrupt in idle task. For example, it warns > > if we put a kprobe on a function called from idle task as below. > > The warning message showed that the rcu_read_lock() caused this > > problem. But actually, this means the RCU is lost the context which > > is already in NMI/IRQ. > > > So make debug exception visible to RCU can fix this warning. > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > index 9568c116ac7f..a6b244240db6 100644 > > --- a/arch/arm64/mm/fault.c > > +++ b/arch/arm64/mm/fault.c > > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > > debug_fault_info[nr].name = name; > > } > > > > +/* > > + * In debug exception context, we explicitly disable preemption. > > + * This serves two purposes: it makes it much less likely that we would > > + * accidentally schedule in exception context and it will force a warning > > + * if we somehow manage to schedule by accident. > > + */ > > +static void debug_exception_enter(struct pt_regs *regs) > > +{ > > + if (user_mode(regs)) { > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > > Would moving entry.S's context_tracking_user_exit() call to be before do_debug_exception() > also fix this? It sounds like treating only user context, correct? This part is just adding assertion, not fixing the problem which Naresh reported. > > I don't know the reason its done 'after' debug exception handling. Its always been like > this: commit 6c81fe7925cc4c42 ("arm64: enable context tracking"). > > > > + } else { > > + /* > > + * We might have interrupted pretty much anything. In > > + * fact, if we're a debug exception, we can even interrupt > > + * NMI processing. > > > + * We don't want in_nmi() to return true, > > + * but we need to notify RCU. > > How come? If you interrupted an SError or pseudo-nmi, it already is. Those paths should > all be painted no-kprobe, but I'm sure there are gaps. The hw-breakpoints can almost > certainly hook them. I think that sentense means "we don't want that this code makes in_nmi() to return true" So, if the breakpoint interrupts pNMI/SError context, it is OK that in_nmi() returns true. > > > > + */ > > + rcu_nmi_enter(); > > Can we interrupt printk()? Do we need printk_nmi_enter()? ... What about ftrace? Good point! As far as I know, we don't use it because ftrace doesn't use printk. But indeed, kprobes user can use printk and they have to call printk_nmi_enter()/exit(), that must be commented in the documentation. Anyway, basically it is user's choice. > > Because SError and pseudo-nmi can interrupt interrupt-masked code, we describe them as > NMI. The only difference here is these exceptions are synchronous. > > > I suspect we should make these debug exceptions nmi for EL1. We can then use this for the > kprobe-re-entrance stuff so the pre/post hooks don't get run if they interrupted something > also described as NMI. I'm not sure how it can prevent... anyway because we have to run a single-stepping for recovery, and kprobe already check the reentered kprobes and skip user-handlers in such case. Thank you, > > > > + } > > + > > + preempt_disable(); > > + > > + /* This code is a bit fragile. Test it. */ > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); > > +} > > +NOKPROBE_SYMBOL(debug_exception_enter); > > > Thanks, > > James
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 9568c116ac7f..a6b244240db6 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, debug_fault_info[nr].name = name; } +/* + * In debug exception context, we explicitly disable preemption. + * This serves two purposes: it makes it much less likely that we would + * accidentally schedule in exception context and it will force a warning + * if we somehow manage to schedule by accident. + */ +static void debug_exception_enter(struct pt_regs *regs) +{ + if (user_mode(regs)) { + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); + } else { + /* + * We might have interrupted pretty much anything. In + * fact, if we're a debug exception, we can even interrupt + * NMI processing. We don't want in_nmi() to return true, + * but we need to notify RCU. + */ + rcu_nmi_enter(); + } + + preempt_disable(); + + /* This code is a bit fragile. Test it. */ + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); +} +NOKPROBE_SYMBOL(debug_exception_enter); + +static void debug_exception_exit(struct pt_regs *regs) +{ + preempt_enable_no_resched(); + + if (!user_mode(regs)) + rcu_nmi_exit(); +} +NOKPROBE_SYMBOL(debug_exception_exit); + #ifdef CONFIG_ARM64_ERRATUM_1463225 DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); @@ -824,6 +860,8 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, if (interrupts_enabled(regs)) trace_hardirqs_off(); + debug_exception_enter(regs); + if (user_mode(regs) && !is_ttbr0_addr(pc)) arm64_apply_bp_hardening(); @@ -832,6 +870,8 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, inf->sig, inf->code, (void __user *)pc, esr); } + debug_exception_exit(regs); + if (interrupts_enabled(regs)) trace_hardirqs_on(); }
Make debug exceptions visible from RCU so that synchronize_rcu() correctly track the debug exception handler. This also introduces sanity checks for user-mode exceptions as same as x86's ist_enter()/ist_exit(). The debug exception can interrupt in idle task. For example, it warns if we put a kprobe on a function called from idle task as below. The warning message showed that the rcu_read_lock() caused this problem. But actually, this means the RCU is lost the context which is already in NMI/IRQ. /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable /sys/kernel/debug/tracing # [ 135.122237] [ 135.125035] ============================= [ 135.125310] WARNING: suspicious RCU usage [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted [ 135.125904] ----------------------------- [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! [ 135.126839] [ 135.126839] other info that might help us debug this: [ 135.126839] [ 135.127410] [ 135.127410] RCU used illegally from idle CPU! [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 [ 135.128114] RCU used illegally from extended quiescent state! [ 135.128555] 1 lock held by swapper/0/0: [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 [ 135.130499] [ 135.130499] stack backtrace: [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 [ 135.131841] Hardware name: linux,dummy-virt (DT) [ 135.132224] Call trace: [ 135.132491] dump_backtrace+0x0/0x140 [ 135.132806] show_stack+0x24/0x30 [ 135.133133] dump_stack+0xc4/0x10c [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 [ 135.134171] call_break_hook+0x170/0x178 [ 135.134486] brk_handler+0x28/0x68 [ 135.134792] do_debug_exception+0x90/0x150 [ 135.135051] el1_dbg+0x18/0x8c [ 135.135260] default_idle_call+0x0/0x44 [ 135.135516] cpu_startup_entry+0x2c/0x30 [ 135.135815] rest_init+0x1b0/0x280 [ 135.136044] arch_call_rest_init+0x14/0x1c [ 135.136305] start_kernel+0x4d4/0x500 [ 135.136597] So make debug exception visible to RCU can fix this warning. Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> Cc: Paul E. McKenney <paulmck@linux.ibm.com> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> --- arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+)