Re: [Qemu-devel] [Bug 1835839] Re: qemu-user: $0 incorrectly always reports absolute path

[Laurent Vivier]

Le 09/07/2019 à 14:16, Peter Maydell a écrit :
> Is the proposed patch backwards compatible (ie "old QEMU binary works
> with newer binfmt-misc registration" and "new QEMU binary works with
> older binfmt-misc registration") ? Because binfmt-misc stuff is whole-
> system but QEMU binaries are per-chroot, this kind of thing is awkward
> to change if we don't have back-compat (and typically the kernel
> semantics for these things often don't allow back-compat or any kind of
> migration-path to the new better setup :-( )
> 

If you don't enable the preserve-arg[0] flag, old and new QEMU will work.

If you enable the flag, only new QEMU with -0/QEMU_ARGV0 will work.

The best solution would be to force preserve-arg[0] with open-binary
flag and rely on AT_FDEXEC to detect the binfmt-misc environment, but
this breaks compatibility with existing environment and old QEMU.

Regarding the "binfmt-misc stuff is whole-system" problem, I've proposed
months ago a kernel based solution [1] to have a configuration per
namespace (chroot), but no one seems really interested (I think
maintainer is afraid by potential security issues).

[1] ns: introduce binfmt_misc namespace
    https://patchwork.kernel.org/cover/10634807/