uselib hasn't been used since libc5; glibc does not use it. Support
turning it off.
When disabled, also omit the load_elf_library implementation from
binfmt_elf.c, which only uselib invokes.
bloat-o-meter:
add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-785 (-785)
function old new delta
padzero 39 36 -3
uselib_flags 20 - -20
sys_uselib 168 - -168
SyS_uselib 168 - -168
load_elf_library 426 - -426
Signed-off-by: Josh Triplett <[email protected]>
---
fs/binfmt_elf.c | 9 ++++++++-
fs/exec.c | 2 ++
init/Kconfig | 9 +++++++++
kernel/sys_ni.c | 1 +
4 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 67be295..0f59799 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -46,10 +46,15 @@
#endif
static int load_elf_binary(struct linux_binprm *bprm);
-static int load_elf_library(struct file *);
static unsigned long elf_map(struct file *, unsigned long, struct elf_phdr *,
int, int, unsigned long);
+#ifdef CONFIG_USELIB
+static int load_elf_library(struct file *);
+#else
+#define load_elf_library NULL
+#endif
+
/*
* If we don't support core dumping, then supply a NULL so we
* don't even try.
@@ -1005,6 +1010,7 @@ out_free_ph:
goto out;
}
+#ifdef CONFIG_USELIB
/* This is really simpleminded and specialized - we are loading an
a.out library that is given an ELF header. */
static int load_elf_library(struct file *file)
@@ -1083,6 +1089,7 @@ out_free_ph:
out:
return error;
}
+#endif /* #ifdef CONFIG_USELIB */
#ifdef CONFIG_ELF_CORE
/*
diff --git a/fs/exec.c b/fs/exec.c
index 3d78fcc..48eb039 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -97,6 +97,7 @@ static inline void put_binfmt(struct linux_binfmt * fmt)
module_put(fmt->module);
}
+#ifdef CONFIG_USELIB
/*
* Note that a shared library must be both readable and executable due to
* security reasons.
@@ -156,6 +157,7 @@ exit:
out:
return error;
}
+#endif /* #ifdef CONFIG_USELIB */
#ifdef CONFIG_MMU
/*
diff --git a/init/Kconfig b/init/Kconfig
index 009a797..d205502 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -273,6 +273,15 @@ config FHANDLE
get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
syscalls.
+config USELIB
+ bool "uselib syscall"
+ help
+ This option enables the uselib syscall, a system call used in the
+ dynamic linker from libc5 and earlier. glibc does not use this
+ system call. If you intend to run programs built on libc5 or
+ earlier, you may need to enable this syscall. Current systems
+ running glibc can safely disable this.
+
config AUDIT
bool "Auditing support"
depends on NET
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 7078052..4177e3e 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -151,6 +151,7 @@ cond_syscall(sys_process_vm_readv);
cond_syscall(sys_process_vm_writev);
cond_syscall(compat_sys_process_vm_readv);
cond_syscall(compat_sys_process_vm_writev);
+cond_syscall(sys_uselib);
/* arch-specific weak syscall entries */
cond_syscall(sys_pciconfig_read);
--
1.9.0
On Fri, 21 Feb 2014 10:11:06 -0800 Josh Triplett <[email protected]> wrote:
> uselib hasn't been used since libc5; glibc does not use it. Support
> turning it off.
>
> When disabled, also omit the load_elf_library implementation from
> binfmt_elf.c, which only uselib invokes.
>
> bloat-o-meter:
> add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-785 (-785)
> function old new delta
> padzero 39 36 -3
> uselib_flags 20 - -20
> sys_uselib 168 - -168
> SyS_uselib 168 - -168
> load_elf_library 426 - -426
>
The patch disables CONFIG_USELIB by default. This important decision
should be mentioned and justified in the changelog, please.
> +#ifdef CONFIG_USELIB
I wonder if CONFIG_SYS_USELIB would be a better identifier. We haven't
done anything consistent here.
On Fri, Feb 21, 2014 at 12:16:27PM -0800, Andrew Morton wrote:
> On Fri, 21 Feb 2014 10:11:06 -0800 Josh Triplett <[email protected]> wrote:
> > uselib hasn't been used since libc5; glibc does not use it. Support
> > turning it off.
> >
> > When disabled, also omit the load_elf_library implementation from
> > binfmt_elf.c, which only uselib invokes.
> >
> > bloat-o-meter:
> > add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-785 (-785)
> > function old new delta
> > padzero 39 36 -3
> > uselib_flags 20 - -20
> > sys_uselib 168 - -168
> > SyS_uselib 168 - -168
> > load_elf_library 426 - -426
> >
>
> The patch disables CONFIG_USELIB by default. This important decision
> should be mentioned and justified in the changelog, please.
Gah, that was not intentional. Will fix in v2. I did very
intentionally not make it require CONFIG_EXPERT or CONFIG_EMBEDDED,
since (like CONFIG_BINFMT_AOUT) almost everyone will want it disabled,
but I had intended to make it "default y".
> > +#ifdef CONFIG_USELIB
>
> I wonder if CONFIG_SYS_USELIB would be a better identifier. We haven't
> done anything consistent here.
As far as I can tell, there's no use of CONFIG_SYS_* or any other
consistent prefix for configuring out syscalls; all such symbols appear
unprefixed. I think it would make sense to have a single common menu
and prefix for configuring out unused syscalls, but given the large
number of existing Kconfig options for that, I think that change ought
to occur as a separate patch series that isn't also trying to add a new
such option.
Perhaps Dave Hansen (CCed) might be interested in incorporating such a
change into his ongoing kconfig consolidation and reorganization?
- Josh Triplett
uselib hasn't been used since libc5; glibc does not use it. Support
turning it off.
When disabled, also omit the load_elf_library implementation as part of
the binfmt, which only uselib invokes.
bloat-o-meter:
add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-785 (-785)
function old new delta
padzero 39 36 -3
uselib_flags 20 - -20
sys_uselib 168 - -168
SyS_uselib 168 - -168
load_elf_library 426 - -426
Signed-off-by: Josh Triplett <[email protected]>
---
v2: Add "default y", unintentionally omitted from the first patch.
Andrew, can you please replace the patch in -mm with this one?
fs/binfmt_elf.c | 9 ++++++++-
fs/exec.c | 2 ++
init/Kconfig | 10 ++++++++++
kernel/sys_ni.c | 1 +
4 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 67be295..0f59799 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -46,10 +46,15 @@
#endif
static int load_elf_binary(struct linux_binprm *bprm);
-static int load_elf_library(struct file *);
static unsigned long elf_map(struct file *, unsigned long, struct elf_phdr *,
int, int, unsigned long);
+#ifdef CONFIG_USELIB
+static int load_elf_library(struct file *);
+#else
+#define load_elf_library NULL
+#endif
+
/*
* If we don't support core dumping, then supply a NULL so we
* don't even try.
@@ -1005,6 +1010,7 @@ out_free_ph:
goto out;
}
+#ifdef CONFIG_USELIB
/* This is really simpleminded and specialized - we are loading an
a.out library that is given an ELF header. */
static int load_elf_library(struct file *file)
@@ -1083,6 +1089,7 @@ out_free_ph:
out:
return error;
}
+#endif /* #ifdef CONFIG_USELIB */
#ifdef CONFIG_ELF_CORE
/*
diff --git a/fs/exec.c b/fs/exec.c
index 3d78fcc..48eb039 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -97,6 +97,7 @@ static inline void put_binfmt(struct linux_binfmt * fmt)
module_put(fmt->module);
}
+#ifdef CONFIG_USELIB
/*
* Note that a shared library must be both readable and executable due to
* security reasons.
@@ -156,6 +157,7 @@ exit:
out:
return error;
}
+#endif /* #ifdef CONFIG_USELIB */
#ifdef CONFIG_MMU
/*
diff --git a/init/Kconfig b/init/Kconfig
index 009a797..7f295a3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -273,6 +273,16 @@ config FHANDLE
get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
syscalls.
+config USELIB
+ bool "uselib syscall"
+ default y
+ help
+ This option enables the uselib syscall, a system call used in the
+ dynamic linker from libc5 and earlier. glibc does not use this
+ system call. If you intend to run programs built on libc5 or
+ earlier, you may need to enable this syscall. Current systems
+ running glibc can safely disable this.
+
config AUDIT
bool "Auditing support"
depends on NET
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 7078052..4177e3e 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -151,6 +151,7 @@ cond_syscall(sys_process_vm_readv);
cond_syscall(sys_process_vm_writev);
cond_syscall(compat_sys_process_vm_readv);
cond_syscall(compat_sys_process_vm_writev);
+cond_syscall(sys_uselib);
/* arch-specific weak syscall entries */
cond_syscall(sys_pciconfig_read);
--
1.9.0