Re: [PATCH v3] binfmt_misc: pass binfmt_misc flags to the interpreter

From: YunQiang Su
Date: Tue Feb 23 2021 - 00:34:58 EST

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Helge Deller <deller@xxxxxx> 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:
> > Le 28/01/2020 à 14:25, Laurent Vivier a écrit :
> >> 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 <laurent@xxxxxxxxx>
>
> Acked-by: Helge Deller <deller@xxxxxx>
>
> 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
>
>
> >> ---
> >>
> >> 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 */
> >>
> >
>

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