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SubjectRe: [PATCH v3] binfmt_misc: pass binfmt_misc flags to the interpreter
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Hi,

any comment?

I think I've addressed comments on v2.

Thanks,
Laurent

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@vivier.eu>
> ---
>
> 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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