binfmt_misc: pass binfmt_misc P flag to the interpreter
Commit Message
From: Laurent Vivier <laurent@vivier.eu>
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>
Signed-off-by: YunQiang Su <syq@debian.org>
---
Notes:
This patch uses AT_FLAGS, which has never been used. We need to make a decision.
since it is about the fundmental API of userland.
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
v4: Update to merge with linux-next: 20200305.
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 | 6 ++++--
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(+), 4 deletions(-)
Comments
* YunQiang Su:
> + if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
> + flags |= AT_FLAGS_PRESERVE_ARGV0;
> + NEW_AUX_ENT(AT_FLAGS, flags);
Is it necessary to reuse AT_FLAGS? I think it's cleaner to define a
separate AT_ tag dedicated to binfmt_misc.
Le 06/03/2020 à 09:13, Florian Weimer a écrit :
> * YunQiang Su:
>
>> + if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
>> + flags |= AT_FLAGS_PRESERVE_ARGV0;
>> + NEW_AUX_ENT(AT_FLAGS, flags);
>
> Is it necessary to reuse AT_FLAGS? I think it's cleaner to define a
> separate AT_ tag dedicated to binfmt_misc.
>
Not necessary, but it seemed simpler and cleaner to re-use a flag that
is marked as unused and with a name matching the new role. It avoids to
patch other packages (like glibc) to add it as it is already defined.
Thanks,
Laurent
* Laurent Vivier:
> Le 06/03/2020 à 09:13, Florian Weimer a écrit :
>> * YunQiang Su:
>>
>>> + if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
>>> + flags |= AT_FLAGS_PRESERVE_ARGV0;
>>> + NEW_AUX_ENT(AT_FLAGS, flags);
>>
>> Is it necessary to reuse AT_FLAGS? I think it's cleaner to define a
>> separate AT_ tag dedicated to binfmt_misc.
>
> Not necessary, but it seemed simpler and cleaner to re-use a flag that
> is marked as unused and with a name matching the new role. It avoids to
> patch other packages (like glibc) to add it as it is already defined.
You still need to define AT_FLAGS_PRESERVE_ARGV0. At that point, you
might as well define AT_BINFMT and AT_BINFMT_PRESERVE_ARGV0.
Le 06/03/2020 à 09:37, Florian Weimer a écrit :
> * Laurent Vivier:
>
>> Le 06/03/2020 à 09:13, Florian Weimer a écrit :
>>> * YunQiang Su:
>>>
>>>> + if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
>>>> + flags |= AT_FLAGS_PRESERVE_ARGV0;
>>>> + NEW_AUX_ENT(AT_FLAGS, flags);
>>>
>>> Is it necessary to reuse AT_FLAGS? I think it's cleaner to define a
>>> separate AT_ tag dedicated to binfmt_misc.
>>
>> Not necessary, but it seemed simpler and cleaner to re-use a flag that
>> is marked as unused and with a name matching the new role. It avoids to
>> patch other packages (like glibc) to add it as it is already defined.
>
> You still need to define AT_FLAGS_PRESERVE_ARGV0. At that point, you
> might as well define AT_BINFMT and AT_BINFMT_PRESERVE_ARGV0.
>
Yes, you're right.
But is there any reason to not reuse AT_FLAGS?
Thanks,
Laurent
Laurent Vivier <laurent@vivier.eu> 于2020年3月6日周五 下午7:13写道：
>
> Le 06/03/2020 à 09:37, Florian Weimer a écrit :
> > * Laurent Vivier:
> >
> >> Le 06/03/2020 à 09:13, Florian Weimer a écrit :
> >>> * YunQiang Su:
> >>>
> >>>> + if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
> >>>> + flags |= AT_FLAGS_PRESERVE_ARGV0;
> >>>> + NEW_AUX_ENT(AT_FLAGS, flags);
> >>>
> >>> Is it necessary to reuse AT_FLAGS? I think it's cleaner to define a
> >>> separate AT_ tag dedicated to binfmt_misc.
> >>
> >> Not necessary, but it seemed simpler and cleaner to re-use a flag that
> >> is marked as unused and with a name matching the new role. It avoids to
> >> patch other packages (like glibc) to add it as it is already defined.
> >
> > You still need to define AT_FLAGS_PRESERVE_ARGV0. At that point, you
> > might as well define AT_BINFMT and AT_BINFMT_PRESERVE_ARGV0.
> >
>
> Yes, you're right.
>
> But is there any reason to not reuse AT_FLAGS?
AT_* only has 32 slot and now. I was afraid that maybe we shouldn't take one.
/* AT_* values 18 through 22 are reserved */
27,28,29,30 are not used now.
Which should we use?
>
> Thanks,
> Laurent
* YunQiang Su:
> AT_* only has 32 slot and now. I was afraid that maybe we shouldn't take one.
> /* AT_* values 18 through 22 are reserved */
> 27,28,29,30 are not used now.
> Which should we use?
Where does this limit of 32 tags come from? I don't see it from a
userspace perspective.
Florian Weimer <fw@deneb.enyo.de> 于2020年3月6日周五 下午7:42写道：
>
> * YunQiang Su:
>
> > AT_* only has 32 slot and now. I was afraid that maybe we shouldn't take one.
> > /* AT_* values 18 through 22 are reserved */
> > 27,28,29,30 are not used now.
> > Which should we use?
>
> Where does this limit of 32 tags come from? I don't see it from a
> userspace perspective.
Sorry it is my mistake: In linux/auxvec.h, I saw
#define AT_RANDOM 25 /* address of 16 random bytes */
#define AT_HWCAP2 26 /* extension of AT_HWCAP */
#define AT_EXECFN 31 /* filename of program */
The number jump to 31 from 26.
It is my fault: in x86_64-linux-gnu/bits/auxv.h, the max number is 47 now.
* YunQiang Su:
> Florian Weimer <fw@deneb.enyo.de> 于2020年3月6日周五 下午7:42写道：
>>
>> * YunQiang Su:
>>
>> > AT_* only has 32 slot and now. I was afraid that maybe we shouldn't take one.
>> > /* AT_* values 18 through 22 are reserved */
>> > 27,28,29,30 are not used now.
>> > Which should we use?
>>
>> Where does this limit of 32 tags come from? I don't see it from a
>> userspace perspective.
>
> Sorry it is my mistake: In linux/auxvec.h, I saw
>
> #define AT_RANDOM 25 /* address of 16 random bytes */
> #define AT_HWCAP2 26 /* extension of AT_HWCAP */
>
> #define AT_EXECFN 31 /* filename of program */
>
> The number jump to 31 from 26.
>
> It is my fault: in x86_64-linux-gnu/bits/auxv.h, the max number is 47 now.
So AT_* tags aren't a scarce resource after all?
Le 06/03/2020 à 12:48, YunQiang Su a écrit :
> Florian Weimer <fw@deneb.enyo.de> 于2020年3月6日周五 下午7:42写道：
>>
>> * YunQiang Su:
>>
>>> AT_* only has 32 slot and now. I was afraid that maybe we shouldn't take one.
>>> /* AT_* values 18 through 22 are reserved */
>>> 27,28,29,30 are not used now.
>>> Which should we use?
>>
>> Where does this limit of 32 tags come from? I don't see it from a
>> userspace perspective.
>
> Sorry it is my mistake: In linux/auxvec.h, I saw
>
> #define AT_RANDOM 25 /* address of 16 random bytes */
> #define AT_HWCAP2 26 /* extension of AT_HWCAP */
>
> #define AT_EXECFN 31 /* filename of program */
>
> The number jump to 31 from 26.
>
> It is my fault: in x86_64-linux-gnu/bits/auxv.h, the max number is 47 now.
>
Numbers starting from 32 are arch specific.
18 to 22 are also reserved (and used by some archs).
(linux/arch/*/include/uapi/asm/auxvec.h)
So there is only 4 entries available (27 to 30)
(linux/include/uapi/linux/auxvec.h)
Do we want to waste one more entry whereas we can use an unused one?
Thanks,
Laurent
@@ -178,7 +178,7 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
const char *k_base_platform = ELF_BASE_PLATFORM;
unsigned char k_rand_bytes[16];
int items;
- elf_addr_t *elf_info;
+ elf_addr_t *elf_info, flags = 0;
int ei_index;
const struct cred *cred = current_cred();
struct vm_area_struct *vma;
@@ -253,7 +253,9 @@ create_elf_tables(struct linux_binprm *bprm, const 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, 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));
@@ -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));
@@ -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;
@@ -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;
@@ -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 */