On Tue, Mar 26, 2024 at 09:15:14AM -0700, Calvin Owens wrote: > On Wednesday 03/27 at 00:24 +0900, Masami Hiramatsu wrote: > > On Tue, 26 Mar 2024 14:46:10 +0000 > > Mark Rutland <mark.rutl...@arm.com> wrote: > > > Different exectuable allocations can have different requirements. For > > > example, > > > on arm64 modules need to be within 2G of the kernel image, but the > > > kprobes XOL > > > areas can be anywhere in the kernel VA space. > > > > > > Forcing those behind the same interface makes things *harder* for > > > architectures > > > and/or makes the common code more complicated (if that ends up having to > > > track > > > all those different requirements). From my PoV it'd be much better to have > > > separate kprobes_alloc_*() functions for kprobes which an architecture > > > can then > > > choose to implement using a common library if it wants to. > > > > > > I took a look at doing that using the core ifdeffery fixups from Jarkko's > > > v6, > > > and it looks pretty clean to me (and works in testing on arm64): > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=kprobes/without-modules > > > > > > Could we please start with that approach, with kprobe-specific alloc/free > > > code > > > provided by the architecture? > > Heh, I also noticed that dead !RWX branch in arm64 patch_map(), I was > about to send a patch to remove it. > > > OK, as far as I can read the code, this method also works and neat! > > (and minimum intrusion). I actually found that exposing CONFIG_ALLOC_EXECMEM > > to user does not help, it should be an internal change. So hiding this > > change > > from user is better choice. Then there is no reason to introduce the new > > alloc_execmem, but just expand kprobe_alloc_insn_page() is reasonable. > > I'm happy with this, it solves the first half of my problem. But I want > eBPF to work in the !MODULES case too. > > I think Mark's approach can work for bpf as well, without needing to > touch module_alloc() at all? So I might be able to drop that first patch > entirely.
I'd be very happy with eBPF following the same approach, with BPF-specific alloc/free functions that we can implement in arch code. IIUC eBPF code *does* want to be within range of the core kernel image, so for arm64 we'd want to factor some common logic out of module_alloc() and into something that module_alloc() and "bpf_alloc()" (or whatever it would be called) could use. So I don't think we'd necessarily save on touching module_alloc(), but I think the resulting split would be better. Thanks, Mark.
