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linux-user: manage binfmt-misc preserve-arg[0] flag 

Add --preserve-argv0 in qemu-binfmt-conf.sh to configure the preserve-argv0
flag.

This patch allows to use new flag in AT_FLAGS to detect if
preserve-argv0 is configured for this interpreter:
argv[0] (the full pathname provided by binfmt-misc) is removed and
replaced by argv[1] (the original argv[0] provided by binfmt-misc when
'P'/preserve-arg[0] is set)

For instance with this patch and kernel support for AT_FLAGS:

  $ sudo chroot m68k-chroot sh -c 'echo $0'
  sh

without this patch:

  $ sudo chroot m68k-chroot sh -c 'echo $0'
  /usr/bin/sh

The new flag is available in kernel (v5.12) since:
2347961b11d4 ("binfmt_misc: pass binfmt_misc flags to the interpreter")

This can be tested with something like:

  # cp ..../qemu-ppc /chroot/powerpc/jessie

  # qemu-binfmt-conf.sh --qemu-path / --systemd ppc --credential yes \
                        --persistent no --preserve-argv0 yes
  # systemctl restart systemd-binfmt.service
  # cat /proc/sys/fs/binfmt_misc/qemu-ppc
  enabled
  interpreter //qemu-ppc
  flags: POC
  offset 0
  magic 7f454c4601020100000000000000000000020014
  mask ffffffffffffff00fffffffffffffffffffeffff
  # chroot /chroot/powerpc/jessie  sh -c 'echo $0'
  sh

  # qemu-binfmt-conf.sh --qemu-path / --systemd ppc --credential yes \
                        --persistent no --preserve-argv0 no
  # systemctl restart systemd-binfmt.service
  # cat /proc/sys/fs/binfmt_misc/qemu-ppc
  enabled
  interpreter //qemu-ppc
  flags: OC
  offset 0
  magic 7f454c4601020100000000000000000000020014
  mask ffffffffffffff00fffffffffffffffffffeffff
  # chroot /chroot/powerpc/jessie  sh -c 'echo $0'
  /bin/sh

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210222105004.1642234-1-laurent@vivier.eu>
This commit is contained in:
Laurent Vivier 2021-02-22 11:50:04 +01:00
parent 08f3a96b33
commit 6e1c0d7b95
2 changed files with 51 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
linux-user/main.c
View File

@ -26,6 +26,7 @@
#include <sys/syscall.h>
#include <sys/resource.h>
#include <sys/shm.h>
#include <linux/binfmts.h>
#include "qapi/error.h"
#include "qemu.h"
@ -49,6 +50,11 @@
#include "cpu_loop-common.h"
#include "crypto/init.h"
#ifndef AT_FLAGS_PRESERVE_ARGV0
#define AT_FLAGS_PRESERVE_ARGV0_BIT 0
#define AT_FLAGS_PRESERVE_ARGV0 (1 << AT_FLAGS_PRESERVE_ARGV0_BIT)
#endif
char *exec_path;
int singlestep;
@ -632,6 +638,7 @@ int main(int argc, char **argv, char **envp)
int execfd;
int log_mask;
unsigned long max_reserved_va;
bool preserve_argv0;
error_init(argv[0]);
module_call_init(MODULE_INIT_TRACE);
@ -688,6 +695,9 @@ int main(int argc, char **argv, char **envp)
init_qemu_uname_release();
/*
* Manage binfmt-misc open-binary flag
*/
execfd = qemu_getauxval(AT_EXECFD);
if (execfd == 0) {
execfd = open(exec_path, O_RDONLY);
@ -697,6 +707,20 @@ int main(int argc, char **argv, char **envp)
}
}
/*
* get binfmt_misc flags
*/
preserve_argv0 = !!(qemu_getauxval(AT_FLAGS) & AT_FLAGS_PRESERVE_ARGV0);
/*
* Manage binfmt-misc preserve-arg[0] flag
* argv[optind] full path to the binary
* argv[optind + 1] original argv[0]
*/
if (optind + 1 < argc && preserve_argv0) {
optind++;
}
if (cpu_model == NULL) {
cpu_model = cpu_get_model(get_elf_eflags(execfd));
}

44
scripts/qemu-binfmt-conf.sh
View File

@ -178,25 +178,27 @@ usage() {
Usage: qemu-binfmt-conf.sh [--qemu-path PATH][--debian][--systemd CPU]
[--help][--credential yes|no][--exportdir PATH]
[--persistent yes|no][--qemu-suffix SUFFIX]
[--preserve-argv0 yes|no]
Configure binfmt_misc to use qemu interpreter
--help: display this usage
--qemu-path: set path to qemu interpreter ($QEMU_PATH)
--qemu-suffix: add a suffix to the default interpreter name
--debian: don't write into /proc,
instead generate update-binfmts templates
--systemd: don't write into /proc,
instead generate file for systemd-binfmt.service
for the given CPU. If CPU is "ALL", generate a
file for all known cpus
--exportdir: define where to write configuration files
(default: $SYSTEMDDIR or $DEBIANDIR)
--credential: if yes, credential and security tokens are
calculated according to the binary to interpret
--persistent: if yes, the interpreter is loaded when binfmt is
configured and remains in memory. All future uses
are cloned from the open file.
--help: display this usage
--qemu-path: set path to qemu interpreter ($QEMU_PATH)
--qemu-suffix: add a suffix to the default interpreter name
--debian: don't write into /proc,
instead generate update-binfmts templates
--systemd: don't write into /proc,
instead generate file for systemd-binfmt.service
for the given CPU. If CPU is "ALL", generate a
file for all known cpus
--exportdir: define where to write configuration files
(default: $SYSTEMDDIR or $DEBIANDIR)
--credential: if yes, credential and security tokens are
calculated according to the binary to interpret
--persistent: if yes, the interpreter is loaded when binfmt is
configured and remains in memory. All future uses
are cloned from the open file.
--preserve-argv0 preserve argv[0]
To import templates with update-binfmts, use :
@ -269,6 +271,9 @@ qemu_generate_register() {
if [ "$PERSISTENT" = "yes" ] ; then
flags="${flags}F"
fi
if [ "$PRESERVE_ARG0" = "yes" ] ; then
flags="${flags}P"
fi
echo ":qemu-$cpu:M::$magic:$mask:$qemu:$flags"
}
@ -330,9 +335,10 @@ DEBIANDIR="/usr/share/binfmts"
QEMU_PATH=/usr/local/bin
CREDENTIAL=no
PERSISTENT=no
PRESERVE_ARG0=no
QEMU_SUFFIX=""
options=$(getopt -o ds:Q:S:e:hc:p: -l debian,systemd:,qemu-path:,qemu-suffix:,exportdir:,help,credential:,persistent: -- "$@")
options=$(getopt -o ds:Q:S:e:hc:p:g: -l debian,systemd:,qemu-path:,qemu-suffix:,exportdir:,help,credential:,persistent:,preserve-argv0: -- "$@")
eval set -- "$options"
while true ; do
@ -388,6 +394,10 @@ while true ; do
shift
PERSISTENT="$1"
;;
-g|--preserve-argv0)
shift
PRESERVE_ARG0="$1"
;;
*)
break
;;