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Teach the verifier about IRQ-disabled sections through the introduction of two new kfuncs, bpf_local_irq_save, to save IRQ state and disable them, and bpf_local_irq_restore, to restore IRQ state and enable them back again. For the purposes of tracking the saved IRQ state, the verifier is taught about a new special object on the stack of type STACK_IRQ_FLAG. This is a 8 byte value which saves the IRQ flags which are to be passed back to the IRQ restore kfunc. Renumber the enums for REF_TYPE_* to simplify the check in find_lock_state, filtering out non-lock types as they grow will become cumbersome and is unecessary. To track a dynamic number of IRQ-disabled regions and their associated saved states, a new resource type RES_TYPE_IRQ is introduced, which its state management functions: acquire_irq_state and release_irq_state, taking advantage of the refactoring and clean ups made in earlier commits. One notable requirement of the kernel's IRQ save and restore API is that they cannot happen out of order. For this purpose, when releasing reference we keep track of the prev_id we saw with REF_TYPE_IRQ. Since reference states are inserted in increasing order of the index, this is used to remember the ordering of acquisitions of IRQ saved states, so that we maintain a logical stack in acquisition order of resource identities, and can enforce LIFO ordering when restoring IRQ state. The top of the stack is maintained using bpf_verifier_state's active_irq_id. To maintain the stack property when releasing reference states, we need to modify release_reference_state to instead shift the remaining array left using memmove instead of swapping deleted element with last that might break the ordering. A selftest to test this subtle behavior is added in late patches. The logic to detect initialized and unitialized irq flag slots, marking and unmarking is similar to how it's done for iterators. No additional checks are needed in refsafe for REF_TYPE_IRQ, apart from the usual check_id satisfiability check on the ref[i].id. We have to perform the same check_ids check on state->active_irq_id as well. To ensure we don't get assigned REF_TYPE_PTR by default after acquire_reference_state, if someone forgets to assign the type, let's also renumber the enum ref_state_type. This way any unassigned types get caught by refsafe's default switch statement, don't assume REF_TYPE_PTR by default. The kfuncs themselves are plain wrappers over local_irq_save and local_irq_restore macros. Acked-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Link: https://lore.kernel.org/r/20241204030400.208005-5-memxor@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.