On Wed, 2024-10-02 at 09:44 -0500, Noah Goldstein wrote: > On Wed, Oct 2, 2024 at 9:38 AM Ilya Leoshkevich <i...@linux.ibm.com> > wrote: > > > > On Wed, 2024-10-02 at 16:08 +0200, Laurent Vivier wrote: > > > Le 02/10/2024 à 10:08, Ilya Leoshkevich a écrit : > > > > On Fri, 2024-08-30 at 15:36 -0700, Noah Goldstein wrote: > > > > > The new option '-qemu-children' makes it so that on `execve` > > > > > the > > > > > child > > > > > process will be launch by the same `qemu` executable that is > > > > > currently > > > > > running along with its current commandline arguments. > > > > > > > > > > The motivation for the change is to make it so that plugins > > > > > running > > > > > through `qemu` can continue to run on children. Why not just > > > > > `binfmt`?: Plugins can be desirable regardless of > > > > > system/architecture > > > > > emulation, and can sometimes be useful for elf files that can > > > > > run > > > > > natively. Enabling `binfmt` for all natively runnable elf > > > > > files > > > > > may > > > > > not be desirable. > > > > > > > > Another reason to have this is that one may not have root > > > > permissions > > > > to configure binfmt-misc. > > > > > > A little note on that: binfmt_misc is now part of the user > > > namespace > > > (since linux v6.7), so you can > > > configure binfmt_misc as a non root user in a given namepace. > > > > > > There is helper to use it with unshare from util-linux, you can > > > do > > > things like that: > > > > > > With 'F' flag, load the interpreter from the initial > > > namespace: > > > > > > $ /bin/qemu-m68k-static --version > > > qemu-m68k version 8.2.2 (qemu-8.2.2-1.fc40) > > > Copyright (c) 2003-2023 Fabrice Bellard and the QEMU Project > > > developers > > > $ unshare --map-root-user --fork --pid > > > --load-interp=":qemu- > > > m68k:M::\\x7fELF\\x01\\x02\\x01\\x00\\x00\\x00\\x00\\x00\\x00\\x0 > > > 0\\x > > > 00\\x00\\x00\\x02\\x00\\x04:\\xff\\xff\\xff\\xff\\xff\\xff\\xfe\\ > > > x00\ > > > \xff\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\xfe\\xff\\xff:/bin/ > > > qemu > > > -m68k-static:OCF" > > > --root=chroot/m68k/sid > > > # QEMU_VERSION= ls > > > qemu-m68k version 8.2.2 (qemu-8.2.2-1.fc40) > > > Copyright (c) 2003-2023 Fabrice Bellard and the QEMU Project > > > developers > > > # /qemu-m68k --version > > > qemu-m68k version 8.0.50 (v8.0.0-340-gb1cff5e2da95) > > > Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project > > > developers > > > > > > Without 'F' flag, from inside the namespace: > > > > > > $ unshare --map-root-user --fork --pid > > > --load-interp=":qemu- > > > m68k:M::\\x7fELF\\x01\\x02\\x01\\x00\\x00\\x00\\x00\\x00\\x00\\x0 > > > 0\\x > > > 00\\x00\\x00\\x02\\x00\\x04:\\xff\\xff\\xff\\xff\\xff\\xff\\xfe\\ > > > x00\ > > > \xff\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\xfe\\xff\\xff:/qemu > > > - > > > m68k:OC" > > > --root=chroot/m68k/sid > > > # QEMU_VERSION= ls > > > qemu-m68k version 8.0.50 (v8.0.0-340-gb1cff5e2da95) > > > Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project > > > developers > > > # /qemu-m68k --version > > > qemu-m68k version 8.0.50 (v8.0.0-340-gb1cff5e2da95) > > > Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project > > > developers > > > > > > Thanks, > > > Laurent > > > > > > > Thanks for posting this, I wasn't aware of this feature and it > > looks > > really useful. > > > > IIUC it also resolves the main problem this patch is dealing with: > > I might misunderstand, but I don't think it does in the sense > that it still might not be desirable to use the same qemu flags > for the entire class of executables. > > I.e the original motivating case was wanting to attach > some plugins to a process and its children and AFAICT > binfmt still doesn't give that level of control.
I think if you start a process in a user namespace, which has a binfmt_misc handler for a certain class of binaries, then this handler will affect only this process and its children, and not the rest of the system. > > Enabling `binfmt` for all natively runnable elf files may > > not be desirable.
