[PATCH bpf-next v1 0/5] vmalloc_exec for modules and BPF programs

[Song Liu <song@kernel.org>]

This set enables bpf programs and bpf dispatchers to share huge pages with
new API:
  vmalloc_exec()
  vfree_exec()
  vcopy_exec()

The idea is similar to Peter's suggestion in [1].

vmalloc_exec() manages a set of PMD_SIZE RO+X memory, and allocates these
memory to its users. vfree_exec() is used to free memory allocated by
vmalloc_exec(). vcopy_exec() is used to update memory allocated by
vmalloc_exec().

Memory allocated by vmalloc_exec() is RO+X, so this doesnot violate W^X.
The caller has to update the content with text_poke like mechanism.
Specifically, vcopy_exec() is provided to update memory allocated by
vmalloc_exec(). vcopy_exec() also makes sure the update stays in the
boundary of one chunk allocated by vmalloc_exec(). Please refer to patch
1/5 for more details of

Patch 3/5 uses these new APIs in bpf program and bpf dispatcher.

Patch 4/5 and 5/5 allows static kernel text (_stext to _etext) to share
PMD_SIZE pages with dynamic kernel text on x86_64. This is achieved by
allocating PMD_SIZE pages to roundup(_etext, PMD_SIZE), and then use
_etext to roundup(_etext, PMD_SIZE) for dynamic kernel text.

[1] https://lore.kernel.org/bpf/Ys6cWUMHO8XwyYgr@hirez.programming.kicks-ass.net/
[2] RFC v1: https://lore.kernel.org/linux-mm/20220818224218.2399791-3-song@kernel.org/T/

Changes RFC v2 => PATCH v1:
1. Add vcopy_exec(), which updates memory allocated by vmalloc_exec(). It
   also ensures vcopy_exec() is only used to update memory from one single
   vmalloc_exec() call. (Christoph Hellwig)
2. Add arch_vcopy_exec() and arch_invalidate_exec() as wrapper for the
   text_poke() like logic.
3. Drop changes for kernel modules and focus on BPF side changes.

Changes RFC v1 => RFC v2:
1. Major rewrite of the logic of vmalloc_exec and vfree_exec. They now
   work fine with BPF programs (patch 1, 2, 4). But module side (patch 3)
   still need some work.

Song Liu (5):
  vmalloc: introduce vmalloc_exec, vfree_exec, and vcopy_exec
  x86/alternative: support vmalloc_exec() and vfree_exec()
  bpf: use vmalloc_exec for bpf program and bpf dispatcher
  vmalloc: introduce register_text_tail_vm()
  x86: use register_text_tail_vm

 arch/x86/include/asm/pgtable_64_types.h |   1 +
 arch/x86/kernel/alternative.c           |  12 +
 arch/x86/mm/init_64.c                   |   4 +-
 arch/x86/net/bpf_jit_comp.c             |  23 +-
 include/linux/bpf.h                     |   3 -
 include/linux/filter.h                  |   5 -
 include/linux/vmalloc.h                 |   9 +
 kernel/bpf/core.c                       | 180 +-----------
 kernel/bpf/dispatcher.c                 |  11 +-
 mm/nommu.c                              |   7 +
 mm/vmalloc.c                            | 351 ++++++++++++++++++++++++
 11 files changed, 404 insertions(+), 202 deletions(-)

--
2.30.2