Helge Deller [off-list ref] 于2021年2月13日周六 下午3:40写道：

On 6/5/20 6:20 PM, Laurent Vivier wrote:

quoted

Le 28/01/2020 à 14:25, Laurent Vivier a écrit :

quoted

It can be useful to the interpreter to know which flags are in use.

For instance, knowing if the preserve-argv[0] is in use would
allow to skip the pathname argument.

This patch uses an unused auxiliary vector, AT_FLAGS, to add a
flag to inform interpreter if the preserve-argv[0] is enabled.

Signed-off-by: Laurent Vivier <redacted>

Acked-by: Helge Deller <deller@gmx.de>

If nobody objects, I'd like to take this patch through the
parisc arch git tree.

Thank you. I see this patch has been in linux-next now.
@Laurent, I guess it is time to work on to push the patch for qemu?

It fixes a real-world problem with qemu-user which fails to
preserve the argv[0] argument when the callee of an exec is a
qemu-user target.
This problem leads to build errors on multiple Debian buildd servers
which are using qemu-user as emulation for the target machines.

For details see Debian bug:
http://bugs.debian.org/970460


Helge

quoted

quoted

---

Notes:
     This can be tested with QEMU from my branch:

       https://github.com/vivier/qemu/commits/binfmt-argv0

     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

     v3: mix my patch with one from YunQiang Su and my comments on it
         introduce a new flag in the uabi for the AT_FLAGS
     v2: only pass special flags (remove Magic and Enabled flags)

  fs/binfmt_elf.c              | 5 ++++-
  fs/binfmt_elf_fdpic.c        | 5 ++++-
  fs/binfmt_misc.c             | 4 +++-
  include/linux/binfmts.h      | 4 ++++
  include/uapi/linux/binfmts.h | 4 ++++
  5 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index ecd8d2698515..ff918042ceed 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c

@@ -176,6 +176,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
     unsigned char k_rand_bytes[16];
     int items;
     elf_addr_t *elf_info;
+    elf_addr_t flags = 0;
     int ei_index = 0;
     const struct cred *cred = current_cred();
     struct vm_area_struct *vma;

@@ -250,7 +251,9 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
     NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
     NEW_AUX_ENT(AT_PHNUM, exec->e_phnum);
     NEW_AUX_ENT(AT_BASE, interp_load_addr);
-    NEW_AUX_ENT(AT_FLAGS, 0);
+    if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
+            flags |= AT_FLAGS_PRESERVE_ARGV0;
+    NEW_AUX_ENT(AT_FLAGS, flags);
     NEW_AUX_ENT(AT_ENTRY, exec->e_entry);
     NEW_AUX_ENT(AT_UID, from_kuid_munged(cred->user_ns, cred->uid));
     NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 240f66663543..abb90d82aa58 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c

@@ -507,6 +507,7 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
     char __user *u_platform, *u_base_platform, *p;
     int loop;
     int nr; /* reset for each csp adjustment */
+    unsigned long flags = 0;

  #ifdef CONFIG_MMU
     /* In some cases (e.g. Hyper-Threading), we want to avoid L1 evictions

@@ -647,7 +648,9 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
     NEW_AUX_ENT(AT_PHENT,   sizeof(struct elf_phdr));
     NEW_AUX_ENT(AT_PHNUM,   exec_params->hdr.e_phnum);
     NEW_AUX_ENT(AT_BASE,    interp_params->elfhdr_addr);
-    NEW_AUX_ENT(AT_FLAGS,   0);
+    if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
+            flags |= AT_FLAGS_PRESERVE_ARGV0;
+    NEW_AUX_ENT(AT_FLAGS,   flags);
     NEW_AUX_ENT(AT_ENTRY,   exec_params->entry_addr);
     NEW_AUX_ENT(AT_UID,     (elf_addr_t) from_kuid_munged(cred->user_ns, cred->uid));
     NEW_AUX_ENT(AT_EUID,    (elf_addr_t) from_kuid_munged(cred->user_ns, cred->euid));

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index cdb45829354d..b9acdd26a654 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c

@@ -154,7 +154,9 @@ static int load_misc_binary(struct linux_binprm *bprm)
     if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
             goto ret;

-    if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
+    if (fmt->flags & MISC_FMT_PRESERVE_ARGV0) {
+            bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
+    } else {
             retval = remove_arg_zero(bprm);
             if (retval)
                     goto ret;

diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index b40fc633f3be..265b80d5fd6f 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h

@@ -78,6 +78,10 @@ struct linux_binprm {
  #define BINPRM_FLAGS_PATH_INACCESSIBLE_BIT 2
  #define BINPRM_FLAGS_PATH_INACCESSIBLE (1 << BINPRM_FLAGS_PATH_INACCESSIBLE_BIT)

+/* if preserve the argv0 for the interpreter  */
+#define BINPRM_FLAGS_PRESERVE_ARGV0_BIT 3
+#define BINPRM_FLAGS_PRESERVE_ARGV0 (1 << BINPRM_FLAGS_PRESERVE_ARGV0_BIT)
+
  /* Function parameter for binfmt->coredump */
  struct coredump_params {
     const kernel_siginfo_t *siginfo;

diff --git a/include/uapi/linux/binfmts.h b/include/uapi/linux/binfmts.h
index 689025d9c185..a70747416130 100644
--- a/include/uapi/linux/binfmts.h
+++ b/include/uapi/linux/binfmts.h

@@ -18,4 +18,8 @@ struct pt_regs;
  /* sizeof(linux_binprm->buf) */
  #define BINPRM_BUF_SIZE 256

+/* if preserve the argv0 for the interpreter  */
+#define AT_FLAGS_PRESERVE_ARGV0_BIT 0
+#define AT_FLAGS_PRESERVE_ARGV0 (1 << AT_FLAGS_PRESERVE_ARGV0_BIT)
+
  #endif /* _UAPI_LINUX_BINFMTS_H */