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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/syscall.h>
#include <sys/resource.h> #include <sys/resource.h>
#include <sys/shm.h> #include <sys/shm.h>
#include <linux/binfmts.h>
#include "qapi/error.h" #include "qapi/error.h"
#include "qemu.h" #include "qemu.h"
@ -49,6 +50,11 @@
#include "cpu_loop-common.h" #include "cpu_loop-common.h"
#include "crypto/init.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; char *exec_path;
int singlestep; int singlestep;
@ -632,6 +638,7 @@ int main(int argc, char **argv, char **envp)
int execfd; int execfd;
int log_mask; int log_mask;
unsigned long max_reserved_va; unsigned long max_reserved_va;
bool preserve_argv0;
error_init(argv[0]); error_init(argv[0]);
module_call_init(MODULE_INIT_TRACE); module_call_init(MODULE_INIT_TRACE);
@ -688,6 +695,9 @@ int main(int argc, char **argv, char **envp)
init_qemu_uname_release(); init_qemu_uname_release();
/*
* Manage binfmt-misc open-binary flag
*/
execfd = qemu_getauxval(AT_EXECFD); execfd = qemu_getauxval(AT_EXECFD);
if (execfd == 0) { if (execfd == 0) {
execfd = open(exec_path, O_RDONLY); 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) { if (cpu_model == NULL) {
cpu_model = cpu_get_model(get_elf_eflags(execfd)); 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] Usage: qemu-binfmt-conf.sh [--qemu-path PATH][--debian][--systemd CPU]
[--help][--credential yes|no][--exportdir PATH] [--help][--credential yes|no][--exportdir PATH]
[--persistent yes|no][--qemu-suffix SUFFIX] [--persistent yes|no][--qemu-suffix SUFFIX]
[--preserve-argv0 yes|no]
Configure binfmt_misc to use qemu interpreter Configure binfmt_misc to use qemu interpreter
--help: display this usage --help: display this usage
--qemu-path: set path to qemu interpreter ($QEMU_PATH) --qemu-path: set path to qemu interpreter ($QEMU_PATH)
--qemu-suffix: add a suffix to the default interpreter name --qemu-suffix: add a suffix to the default interpreter name
--debian: don't write into /proc, --debian: don't write into /proc,
instead generate update-binfmts templates instead generate update-binfmts templates
--systemd: don't write into /proc, --systemd: don't write into /proc,
instead generate file for systemd-binfmt.service instead generate file for systemd-binfmt.service
for the given CPU. If CPU is "ALL", generate a for the given CPU. If CPU is "ALL", generate a
file for all known cpus file for all known cpus
--exportdir: define where to write configuration files --exportdir: define where to write configuration files
(default: $SYSTEMDDIR or $DEBIANDIR) (default: $SYSTEMDDIR or $DEBIANDIR)
--credential: if yes, credential and security tokens are --credential: if yes, credential and security tokens are
calculated according to the binary to interpret calculated according to the binary to interpret
--persistent: if yes, the interpreter is loaded when binfmt is --persistent: if yes, the interpreter is loaded when binfmt is
configured and remains in memory. All future uses configured and remains in memory. All future uses
are cloned from the open file. are cloned from the open file.
--preserve-argv0 preserve argv[0]
To import templates with update-binfmts, use : To import templates with update-binfmts, use :
@ -269,6 +271,9 @@ qemu_generate_register() {
if [ "$PERSISTENT" = "yes" ] ; then if [ "$PERSISTENT" = "yes" ] ; then
flags="${flags}F" flags="${flags}F"
fi fi
if [ "$PRESERVE_ARG0" = "yes" ] ; then
flags="${flags}P"
fi
echo ":qemu-$cpu:M::$magic:$mask:$qemu:$flags" echo ":qemu-$cpu:M::$magic:$mask:$qemu:$flags"
} }
@ -330,9 +335,10 @@ DEBIANDIR="/usr/share/binfmts"
QEMU_PATH=/usr/local/bin QEMU_PATH=/usr/local/bin
CREDENTIAL=no CREDENTIAL=no
PERSISTENT=no PERSISTENT=no
PRESERVE_ARG0=no
QEMU_SUFFIX="" QEMU_SUFFIX=""
options=$(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" eval set -- "$options"
while true ; do while true ; do
@ -388,6 +394,10 @@ while true ; do
shift shift
PERSISTENT="$1" PERSISTENT="$1"
;; ;;
-g|--preserve-argv0)
shift
PRESERVE_ARG0="$1"
;;
*) *)
break break
;; ;;