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tracing/user_events: Add ioctl for disabling addresses

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Enablements are now tracked by the lifetime of the task/mm. User
processes need to be able to disable their addresses if tracing is
requested to be turned off. Before unmapping the page would suffice.
However, we now need a stronger contract. Add an ioctl to enable this.

A new flag bit is added, freeing, to user_event_enabler to ensure that
if the event is attempted to be removed while a fault is being handled
that the remove is delayed until after the fault is reattempted.

Link: https://lkml.kernel.org/r/20230328235219.203-6-beaub@linux.microsoft.com

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Beau Belgrave 2023-03-28 16:52:12 -07:00 committed by Steven Rostedt (Google)
parent 81f8fb6549
commit dcb8177c13
2 changed files with 119 additions and 2 deletions
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24
include/uapi/linux/user_events.h
View File

@ -46,6 +46,27 @@ struct user_reg {
__u32 write_index;
} __attribute__((__packed__));
/*
* Describes an event unregister, callers must set the size, address and bit.
* This structure is passed to the DIAG_IOCSUNREG ioctl to disable bit updates.
*/
struct user_unreg {
/* Input: Size of the user_unreg structure being used */
__u32 size;
/* Input: Bit to unregister */
__u8 disable_bit;
/* Input: Reserved, set to 0 */
__u8 __reserved;
/* Input: Reserved, set to 0 */
__u16 __reserved2;
/* Input: Address to unregister */
__u64 disable_addr;
} __attribute__((__packed__));
#define DIAG_IOC_MAGIC '*'
/* Request to register a user_event */
@ -54,4 +75,7 @@ struct user_reg {
/* Request to delete a user_event */
#define DIAG_IOCSDEL _IOW(DIAG_IOC_MAGIC, 1, char *)
/* Requests to unregister a user_event */
#define DIAG_IOCSUNREG _IOW(DIAG_IOC_MAGIC, 2, struct user_unreg*)
#endif /* _UAPI_LINUX_USER_EVENTS_H */

97
kernel/trace/trace_events_user.c
View File

@ -102,6 +102,9 @@ struct user_event_enabler {
/* Bit 6 is for faulting status of enablement */
#define ENABLE_VAL_FAULTING_BIT 6
/* Bit 7 is for freeing status of enablement */
#define ENABLE_VAL_FREEING_BIT 7
/* Only duplicate the bit value */
#define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK
@ -301,6 +304,12 @@ static void user_event_enabler_fault_fixup(struct work_struct *work)
/* Prevent state changes from racing */
mutex_lock(&event_mutex);
/* User asked for enabler to be removed during fault */
if (test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))) {
user_event_enabler_destroy(enabler);
goto out;
}
/*
* If we managed to get the page, re-issue the write. We do not
* want to get into a possible infinite loop, which is why we only
@ -315,7 +324,7 @@ static void user_event_enabler_fault_fixup(struct work_struct *work)
user_event_enabler_write(mm, enabler, true);
mmap_read_unlock(mm->mm);
}
out:
mutex_unlock(&event_mutex);
/* In all cases we no longer need the mm or fault */
@ -370,7 +379,8 @@ static int user_event_enabler_write(struct user_event_mm *mm,
if (refcount_read(&mm->tasks) == 0)
return -ENOENT;
if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler))))
if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)) ||
test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))))
return -EBUSY;
ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT,
@ -428,6 +438,10 @@ static bool user_event_enabler_dup(struct user_event_enabler *orig,
{
struct user_event_enabler *enabler;
/* Skip pending frees */
if (unlikely(test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(orig))))
return true;
enabler = kzalloc(sizeof(*enabler), GFP_NOWAIT);
if (!enabler)
@ -2086,6 +2100,79 @@ static long user_events_ioctl_del(struct user_event_file_info *info,
return ret;
}
static long user_unreg_get(struct user_unreg __user *ureg,
struct user_unreg *kreg)
{
u32 size;
long ret;
ret = get_user(size, &ureg->size);
if (ret)
return ret;
if (size > PAGE_SIZE)
return -E2BIG;
if (size < offsetofend(struct user_unreg, disable_addr))
return -EINVAL;
ret = copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);
/* Ensure no reserved values, since we don't support any yet */
if (kreg->__reserved || kreg->__reserved2)
return -EINVAL;
return ret;
}
/*
* Unregisters an enablement address/bit within a task/user mm.
*/
static long user_events_ioctl_unreg(unsigned long uarg)
{
struct user_unreg __user *ureg = (struct user_unreg __user *)uarg;
struct user_event_mm *mm = current->user_event_mm;
struct user_event_enabler *enabler, *next;
struct user_unreg reg;
long ret;
ret = user_unreg_get(ureg, &reg);
if (ret)
return ret;
if (!mm)
return -ENOENT;
ret = -ENOENT;
/*
* Flags freeing and faulting are used to indicate if the enabler is in
* use at all. When faulting is set a page-fault is occurring asyncly.
* During async fault if freeing is set, the enabler will be destroyed.
* If no async fault is happening, we can destroy it now since we hold
* the event_mutex during these checks.
*/
mutex_lock(&event_mutex);
list_for_each_entry_safe(enabler, next, &mm->enablers, link)
if (enabler->addr == reg.disable_addr &&
(enabler->values & ENABLE_VAL_BIT_MASK) == reg.disable_bit) {
set_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler));
if (!test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))
user_event_enabler_destroy(enabler);
/* Removed at least one */
ret = 0;
}
mutex_unlock(&event_mutex);
return ret;
}
/*
* Handles the ioctl from user mode to register or alter operations.
*/
@ -2108,6 +2195,12 @@ static long user_events_ioctl(struct file *file, unsigned int cmd,
ret = user_events_ioctl_del(info, uarg);
mutex_unlock(&group->reg_mutex);
break;
case DIAG_IOCSUNREG:
mutex_lock(&group->reg_mutex);
ret = user_events_ioctl_unreg(uarg);
mutex_unlock(&group->reg_mutex);
break;
}
return ret;