On Sat, Nov 30, 2019 at 1:52 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > On 11/30/19 2:37 AM, Eric Dumazet wrote: > > On 11/29/19 2:29 PM, Daniel Borkmann wrote: > >> For the case where the interpreter is compiled out or when the prog is jited > >> it is completely unnecessary to set the BPF insn pages as read-only. In fact, > >> on frequent churn of BPF programs, it could lead to performance degradation of > >> the system over time since it would break the direct map down to 4k pages when > >> calling set_memory_ro() for the insn buffer on x86-64 / arm64 and there is no > >> reverse operation. Thus, avoid breaking up large pages for data maps, and only > >> limit this to the module range used by the JIT where it is necessary to set > >> the image read-only and executable. > > > > Interesting... But why the non JIT case would need RO protection ? > > It was done for interpreter around 5 years ago mainly due to concerns from security > folks that the BPF insn image could get corrupted (through some other bug in the > kernel) in post-verifier stage by an attacker and then there's nothing really that > would provide any sort of protection guarantees; pretty much the same reasons why > e.g. modules are set to read-only in the kernel. > > > Do you have any performance measures to share ? > > No numbers, and I'm also not aware of any reports from users, but it was recently > brought to our attention from mm folks during discussion of a different set: > > https://lore.kernel.org/lkml/1572171452-7958-2-git-send-email-rppt@xxxxxxxxxx/T/ Applied. Thanks
