| Message ID | 1543845318-24543-2-git-send-email-julien.thierry@arm.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | uaccess: Add unsafe accessors for arm64 | expand |
Hi, On 03/12/2018 13:55, Julien Thierry wrote: > While running a user_access regions, it is not supported to reschedule. > Add an overridable primitive to indicate whether a user_access region is > active and check that this is not the case when calling rescheduling > functions. > > Also, add a comment clarifying the behaviour of user_access regions. > > Signed-off-by: Julien Thierry <julien.thierry@arm.com> > --- > include/linux/kernel.h | 6 ++++-- > include/linux/uaccess.h | 11 +++++++++++ > kernel/sched/core.c | 19 +++++++++++++++++++ > 3 files changed, 34 insertions(+), 2 deletions(-) > > I'm not sure these are the best locations to check this but I was hoping > this patch could start the discussion. > > Should I move the check? Should I add a config option to conditionally > build those checks? > I was going to say it's already under DEBUG_ATOMIC_SLEEP, but that's only true for the __might_sleep() bit actually. I think it'd make sense to blanket that under a config, but using DEBUG_ATOMIC_SLEEP for that is a bit too much. What about a DEBUG_UACCESS_SLEEP? > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index d6aac75..fe0e984 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -237,11 +237,13 @@ > struct pt_regs; > struct user; > > +extern void __might_resched(const char *file, int line); > #ifdef CONFIG_PREEMPT_VOLUNTARY > extern int _cond_resched(void); > -# define might_resched() _cond_resched() > +# define might_resched() \ > + do { __might_resched(__FILE__, __LINE__); _cond_resched(); } while (0) > #else > -# define might_resched() do { } while (0) > +# define might_resched() __might_resched(__FILE__, __LINE__)> #endif > > #ifdef CONFIG_DEBUG_ATOMIC_SLEEP > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h > index efe79c1..50adb84 100644 > --- a/include/linux/uaccess.h > +++ b/include/linux/uaccess.h > @@ -266,6 +266,13 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, > #define probe_kernel_address(addr, retval) \ > probe_kernel_read(&retval, addr, sizeof(retval)) > > +/* > + * user_access_begin() and user_access_end() define a region where > + * unsafe user accessors can be used. > + * During execution of this region, no sleeping functions should be called. > + * Exceptions and interrupt shall exit the user_access region and re-enter it > + * when returning to the interrupted context. > + */ I would first have the bit about exceptions, then mention sleeping and add something along the lines of "[...] no sleeping functions should be called - we rely on exception handling to take care of the user_access status for us, but that doesn't happen when directly calling schedule()." My wording's not the best but I just want something to point out *why* sleeping ain't okay. > #ifndef user_access_begin > #define user_access_begin() do { } while (0) > #define user_access_end() do { } while (0) > @@ -273,6 +280,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, > #define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0) > #endif > > +#ifndef unsafe_user_region_active > +#define unsafe_user_region_active() false > +#endif > + > #ifdef CONFIG_HARDENED_USERCOPY > void usercopy_warn(const char *name, const char *detail, bool to_user, > unsigned long offset, unsigned long len); > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 6fedf3a..03f53c8 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3289,6 +3289,13 @@ static inline void schedule_debug(struct task_struct *prev) > __schedule_bug(prev); > preempt_count_set(PREEMPT_DISABLED); > } > + > + if (unlikely(unsafe_user_region_active())) { > + printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n", > + prev->comm, prev->pid, preempt_count()); > + dump_stack(); > + } > + > rcu_sleep_check(); > > profile_hit(SCHED_PROFILING, __builtin_return_address(0)); > @@ -6151,6 +6158,18 @@ void ___might_sleep(const char *file, int line, int preempt_offset) > EXPORT_SYMBOL(___might_sleep); > #endif > > +void __might_resched(const char *file, int line) > +{ > + if (!unsafe_user_region_active()) > + return; > + > + printk(KERN_ERR > + "BUG: rescheduling function called from user access context at %s:%d\n", > + file, line); > + dump_stack(); > +} So this check is "careful, things might go bad" and the schedule_debug() one is "things went bad". IIUC we'll always get this warning when we hit the schedule_debug() one. I was going to suggest only keeping one of them, but I think both hold value. > +EXPORT_SYMBOL(__might_resched); > + > #ifdef CONFIG_MAGIC_SYSRQ > void normalize_rt_tasks(void) > { > -- > 1.9.1 >
Hi, On 14/01/2019 12:03, Valentin Schneider wrote: > Hi, > > On 03/12/2018 13:55, Julien Thierry wrote: >> While running a user_access regions, it is not supported to reschedule. >> Add an overridable primitive to indicate whether a user_access region is >> active and check that this is not the case when calling rescheduling >> functions. >> >> Also, add a comment clarifying the behaviour of user_access regions. >> >> Signed-off-by: Julien Thierry <julien.thierry@arm.com> >> --- >> include/linux/kernel.h | 6 ++++-- >> include/linux/uaccess.h | 11 +++++++++++ >> kernel/sched/core.c | 19 +++++++++++++++++++ >> 3 files changed, 34 insertions(+), 2 deletions(-) >> >> I'm not sure these are the best locations to check this but I was hoping >> this patch could start the discussion. >> >> Should I move the check? Should I add a config option to conditionally >> build those checks? >> > > I was going to say it's already under DEBUG_ATOMIC_SLEEP, but that's only > true for the __might_sleep() bit actually. > > I think it'd make sense to blanket that under a config, but using > DEBUG_ATOMIC_SLEEP for that is a bit too much. What about a > DEBUG_UACCESS_SLEEP? > Yes, I was wondering whether to add something like that, I'll add a DEBUG_UACCESS_SLEEP to my next version. >> diff --git a/include/linux/kernel.h b/include/linux/kernel.h >> index d6aac75..fe0e984 100644 >> --- a/include/linux/kernel.h >> +++ b/include/linux/kernel.h >> @@ -237,11 +237,13 @@ >> struct pt_regs; >> struct user; >> >> +extern void __might_resched(const char *file, int line); >> #ifdef CONFIG_PREEMPT_VOLUNTARY >> extern int _cond_resched(void); >> -# define might_resched() _cond_resched() >> +# define might_resched() \ >> + do { __might_resched(__FILE__, __LINE__); _cond_resched(); } while (0) >> #else >> -# define might_resched() do { } while (0) >> +# define might_resched() __might_resched(__FILE__, __LINE__)> #endif >> >> #ifdef CONFIG_DEBUG_ATOMIC_SLEEP >> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h >> index efe79c1..50adb84 100644 >> --- a/include/linux/uaccess.h >> +++ b/include/linux/uaccess.h >> @@ -266,6 +266,13 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, >> #define probe_kernel_address(addr, retval) \ >> probe_kernel_read(&retval, addr, sizeof(retval)) >> >> +/* >> + * user_access_begin() and user_access_end() define a region where >> + * unsafe user accessors can be used. >> + * During execution of this region, no sleeping functions should be called. >> + * Exceptions and interrupt shall exit the user_access region and re-enter it >> + * when returning to the interrupted context. >> + */ > > I would first have the bit about exceptions, then mention sleeping and add > something along the lines of > > "[...] no sleeping functions should be called - we rely on exception > handling to take care of the user_access status for us, but that doesn't > happen when directly calling schedule()." > > My wording's not the best but I just want something to point out *why* > sleeping ain't okay. > I think the wording is alright, I'll include your suggestion for the next version. >> #ifndef user_access_begin >> #define user_access_begin() do { } while (0) >> #define user_access_end() do { } while (0) >> @@ -273,6 +280,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, >> #define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0) >> #endif >> >> +#ifndef unsafe_user_region_active >> +#define unsafe_user_region_active() false >> +#endif >> + >> #ifdef CONFIG_HARDENED_USERCOPY >> void usercopy_warn(const char *name, const char *detail, bool to_user, >> unsigned long offset, unsigned long len); >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 6fedf3a..03f53c8 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -3289,6 +3289,13 @@ static inline void schedule_debug(struct task_struct *prev) >> __schedule_bug(prev); >> preempt_count_set(PREEMPT_DISABLED); >> } >> + >> + if (unlikely(unsafe_user_region_active())) { >> + printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n", >> + prev->comm, prev->pid, preempt_count()); >> + dump_stack(); >> + } >> + >> rcu_sleep_check(); >> >> profile_hit(SCHED_PROFILING, __builtin_return_address(0)); >> @@ -6151,6 +6158,18 @@ void ___might_sleep(const char *file, int line, int preempt_offset) >> EXPORT_SYMBOL(___might_sleep); >> #endif >> >> +void __might_resched(const char *file, int line) >> +{ >> + if (!unsafe_user_region_active()) >> + return; >> + >> + printk(KERN_ERR >> + "BUG: rescheduling function called from user access context at %s:%d\n", >> + file, line); >> + dump_stack(); >> +} > > So this check is "careful, things might go bad" and the schedule_debug() > one is "things went bad". IIUC we'll always get this warning when we hit > the schedule_debug() one. I was going to suggest only keeping one of them, > but I think both hold value. > Yes, I can't really convince myself to remove either, unless there is a magic place that covers both cases. Thanks for the suggestions. Cheers,
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index d6aac75..fe0e984 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -237,11 +237,13 @@ struct pt_regs; struct user; +extern void __might_resched(const char *file, int line); #ifdef CONFIG_PREEMPT_VOLUNTARY extern int _cond_resched(void); -# define might_resched() _cond_resched() +# define might_resched() \ + do { __might_resched(__FILE__, __LINE__); _cond_resched(); } while (0) #else -# define might_resched() do { } while (0) +# define might_resched() __might_resched(__FILE__, __LINE__) #endif #ifdef CONFIG_DEBUG_ATOMIC_SLEEP diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index efe79c1..50adb84 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -266,6 +266,13 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, #define probe_kernel_address(addr, retval) \ probe_kernel_read(&retval, addr, sizeof(retval)) +/* + * user_access_begin() and user_access_end() define a region where + * unsafe user accessors can be used. + * During execution of this region, no sleeping functions should be called. + * Exceptions and interrupt shall exit the user_access region and re-enter it + * when returning to the interrupted context. + */ #ifndef user_access_begin #define user_access_begin() do { } while (0) #define user_access_end() do { } while (0) @@ -273,6 +280,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, #define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0) #endif +#ifndef unsafe_user_region_active +#define unsafe_user_region_active() false +#endif + #ifdef CONFIG_HARDENED_USERCOPY void usercopy_warn(const char *name, const char *detail, bool to_user, unsigned long offset, unsigned long len); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6fedf3a..03f53c8 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3289,6 +3289,13 @@ static inline void schedule_debug(struct task_struct *prev) __schedule_bug(prev); preempt_count_set(PREEMPT_DISABLED); } + + if (unlikely(unsafe_user_region_active())) { + printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n", + prev->comm, prev->pid, preempt_count()); + dump_stack(); + } + rcu_sleep_check(); profile_hit(SCHED_PROFILING, __builtin_return_address(0)); @@ -6151,6 +6158,18 @@ void ___might_sleep(const char *file, int line, int preempt_offset) EXPORT_SYMBOL(___might_sleep); #endif +void __might_resched(const char *file, int line) +{ + if (!unsafe_user_region_active()) + return; + + printk(KERN_ERR + "BUG: rescheduling function called from user access context at %s:%d\n", + file, line); + dump_stack(); +} +EXPORT_SYMBOL(__might_resched); + #ifdef CONFIG_MAGIC_SYSRQ void normalize_rt_tasks(void) {
While running a user_access regions, it is not supported to reschedule. Add an overridable primitive to indicate whether a user_access region is active and check that this is not the case when calling rescheduling functions. Also, add a comment clarifying the behaviour of user_access regions. Signed-off-by: Julien Thierry <julien.thierry@arm.com> --- include/linux/kernel.h | 6 ++++-- include/linux/uaccess.h | 11 +++++++++++ kernel/sched/core.c | 19 +++++++++++++++++++ 3 files changed, 34 insertions(+), 2 deletions(-) I'm not sure these are the best locations to check this but I was hoping this patch could start the discussion. Should I move the check? Should I add a config option to conditionally build those checks? -- 1.9.1