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Diffstat (limited to 'Documentation/bpf/kfuncs.rst')
| -rw-r--r-- | Documentation/bpf/kfuncs.rst | 39 |
1 files changed, 31 insertions, 8 deletions
diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index c0b7dae6dbf5..0f858156371d 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -137,14 +137,37 @@ KF_ACQUIRE and KF_RET_NULL flags. -------------------------- The KF_TRUSTED_ARGS flag is used for kfuncs taking pointer arguments. It -indicates that the all pointer arguments will always be refcounted, and have -their offset set to 0. It can be used to enforce that a pointer to a refcounted -object acquired from a kfunc or BPF helper is passed as an argument to this -kfunc without any modifications (e.g. pointer arithmetic) such that it is -trusted and points to the original object. This flag is often used for kfuncs -that operate (change some property, perform some operation) on an object that -was obtained using an acquire kfunc. Such kfuncs need an unchanged pointer to -ensure the integrity of the operation being performed on the expected object. +indicates that the all pointer arguments will always have a guaranteed lifetime, +and pointers to kernel objects are always passed to helpers in their unmodified +form (as obtained from acquire kfuncs). + +It can be used to enforce that a pointer to a refcounted object acquired from a +kfunc or BPF helper is passed as an argument to this kfunc without any +modifications (e.g. pointer arithmetic) such that it is trusted and points to +the original object. + +Meanwhile, it is also allowed pass pointers to normal memory to such kfuncs, +but those can have a non-zero offset. + +This flag is often used for kfuncs that operate (change some property, perform +some operation) on an object that was obtained using an acquire kfunc. Such +kfuncs need an unchanged pointer to ensure the integrity of the operation being +performed on the expected object. + +2.4.6 KF_SLEEPABLE flag +----------------------- + +The KF_SLEEPABLE flag is used for kfuncs that may sleep. Such kfuncs can only +be called by sleepable BPF programs (BPF_F_SLEEPABLE). + +2.4.7 KF_DESTRUCTIVE flag +-------------------------- + +The KF_DESTRUCTIVE flag is used to indicate functions calling which is +destructive to the system. For example such a call can result in system +rebooting or panicking. Due to this additional restrictions apply to these +calls. At the moment they only require CAP_SYS_BOOT capability, but more can be +added later. 2.5 Registering the kfuncs -------------------------- |