[PATCH] binfmt_misc: pass binfmt_misc P flag to the interpreter
From: YunQiang Su <hidden>
Date: 2020-03-06 08:09:46
From: Laurent Vivier <redacted>
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 <redacted>
Signed-off-by: YunQiang Su <redacted>
---
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(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 13f25e241ac4..e9f5d135b847 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c@@ -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));
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 */
--
2.25.1