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SubjectRe: [PATCH v3] binfmt_misc: pass binfmt_misc flags to the interpreter
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I'd like to have this in the kernel to be able to use it in QEMU (next
QEMU release is 28/04, freeze 17/03).

Thanks,
Laurent

Le 14/02/2020 à 13:29, Laurent Vivier a écrit :
> 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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