bpf: Fix softlockup in arena_map_free on 64k page kernel

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix softlockup in arena_map_free on 64k page kernel On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y, arena_htab tests cause a segmentation fault and soft lockup. The same failure is not observed with 4k pages on aarch64. It turns out arena_map_free() is calling apply_to_existing_page_range() with the address returned by bpf_arena_get_kern_vm_start(). If this address is not page-aligned the code ends up calling apply_to_pte_range() with that unaligned address causing soft lockup. Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the division by 2 in bpf_arena_get_kern_vm_start() returns a page-aligned value.

References

• https://git.kernel.org/stable/c/c1f3f3892d4526f18aaeffdb6068ce861e793ee3
• https://git.kernel.org/stable/c/787d556a3de447e70964a4bdeba9196f62a62b1e
• https://git.kernel.org/stable/c/517e8a7835e8cfb398a0aeb0133de50e31cae32b