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Subject: Re: [PATCH v3] binfmt_misc: pass binfmt_misc flags to the interpreter
To:     linux-kernel@vger.kernel.org
Cc:     linux-fsdevel@vger.kernel.org, YunQiang Su <ysu@wavecomp.com>,
        YunQiang Su <syq@debian.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        James Bottomley <James.Bottomley@HansenPartnership.com>
References: <20200128132539.782286-1-laurent@vivier.eu>
From:   Laurent Vivier <laurent@vivier.eu>
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Message-ID: <d2993cd1-f671-380c-5887-52c987b84cd0@vivier.eu>
Date:   Fri, 14 Feb 2020 13:29:15 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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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 */
>